Merge pull request #51368 from TwistedTwigleg/GSOC_2020_Working_Branch_IK_SQUASHED

New and improved IK system for Skeleton3D - Squashed!

core/math/basis.cpp

@@ -381,6 +381,18 @@ Quaternion Basis::get_rotation_quaternion() const {
 	return m.get_quaternion();
 }
 
+void Basis::rotate_to_align(Vector3 p_start_direction, Vector3 p_end_direction) {
+	// Takes two vectors and rotates the basis from the first vector to the second vector.
+	// Adopted from: https://gist.github.com/kevinmoran/b45980723e53edeb8a5a43c49f134724
+	const Vector3 axis = p_start_direction.cross(p_end_direction).normalized();
+	if (axis.length_squared() != 0) {
+		real_t dot = p_start_direction.dot(p_end_direction);
+		dot = CLAMP(dot, -1.0, 1.0);
+		const real_t angle_rads = Math::acos(dot);
+		set_axis_angle(axis, angle_rads);
+	}
+}
+
 void Basis::get_rotation_axis_angle(Vector3 &p_axis, real_t &p_angle) const {
 	// Assumes that the matrix can be decomposed into a proper rotation and scaling matrix as M = R.S,
 	// and returns the Euler angles corresponding to the rotation part, complementing get_scale().

core/math/basis.h

@@ -88,6 +88,8 @@ public:
 	Quaternion get_rotation_quaternion() const;
 	Vector3 get_rotation() const { return get_rotation_euler(); };
 
+	void rotate_to_align(Vector3 p_start_direction, Vector3 p_end_direction);
+
 	Vector3 rotref_posscale_decomposition(Basis &rotref) const;
 
 	Vector3 get_euler_xyz() const;

doc/classes/BoneAttachment3D.xml

@@ -4,13 +4,76 @@
 		A node that will attach to a bone.
 	</brief_description>
 	<description>
-		This node must be the child of a [Skeleton3D] node. You can then select a bone for this node to attach to. The BoneAttachment3D node will copy the transform of the selected bone.
+		This node will allow you to select a bone for this node to attach to. The BoneAttachment3D node can copy the transform of the select bone, or can override the transform of the selected bone.
+		The BoneAttachment3D node must either be a child of a [Skeleton3D] node or be given an external [Skeleton3D] to use in order to function properly.
 	</description>
 	<tutorials>
 	</tutorials>
 	<methods>
+		<method name="get_external_skeleton" qualifiers="const">
+			<return type="NodePath" />
+			<description>
+				Returns the [NodePath] to the external [Skeleton3D] node, if one has been set.
+			</description>
+		</method>
+		<method name="get_override_mode" qualifiers="const">
+			<return type="int" />
+			<description>
+				Returns the override mode for the BoneAttachment3D node.
+			</description>
+		</method>
+		<method name="get_override_pose" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns whether the BoneAttachment3D node is overriding the bone pose of the bone it's attached to.
+			</description>
+		</method>
+		<method name="get_use_external_skeleton" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns whether the BoneAttachment3D node is using an external [Skeleton3D] rather than attempting to use its parent node as the [Skeleton3D].
+			</description>
+		</method>
+		<method name="on_bone_pose_update">
+			<return type="void" />
+			<argument index="0" name="bone_index" type="int" />
+			<description>
+				A function that is called automatically when the [Skeleton3D] the BoneAttachment3D node is using has a bone that has changed its pose. This function is where the BoneAttachment3D node updates its position so it is correctly bound when it is [i]not[/i] set to override the bone pose.
+			</description>
+		</method>
+		<method name="set_external_skeleton">
+			<return type="void" />
+			<argument index="0" name="external_skeleton" type="NodePath" />
+			<description>
+				Sets the [NodePath] to the external skeleton that the BoneAttachment3D node should use. The external [Skeleton3D] node is only used when [code]use_external_skeleton[/code] is set to [code]true[/code].
+			</description>
+		</method>
+		<method name="set_override_mode">
+			<return type="void" />
+			<argument index="0" name="override_mode" type="int" />
+			<description>
+				Sets the override mode for the BoneAttachment3D node. The override mode defines which of the bone poses the BoneAttachment3D node will override.
+			</description>
+		</method>
+		<method name="set_override_pose">
+			<return type="void" />
+			<argument index="0" name="override_pose" type="bool" />
+			<description>
+				Sets whether the BoneAttachment3D node will override the bone pose of the bone it is attached to. When set to [code]true[/code], the BoneAttachment3D node can change the pose of the bone.
+			</description>
+		</method>
+		<method name="set_use_external_skeleton">
+			<return type="void" />
+			<argument index="0" name="use_external_skeleton" type="bool" />
+			<description>
+				Sets whether the BoneAttachment3D node will use an extenral [Skeleton3D] node rather than attenpting to use its parent node as the [Skeleton3D]. When set to [code]true[/code], the BoneAttachment3D node will use the external [Skeleton3D] node set in [code]set_external_skeleton[/code].
+			</description>
+		</method>
 	</methods>
 	<members>
+		<member name="bone_idx" type="int" setter="set_bone_idx" getter="get_bone_idx" default="-1">
+			The index of the attached bone.
+		</member>
 		<member name="bone_name" type="String" setter="set_bone_name" getter="get_bone_name" default="&quot;&quot;">
 			The name of the attached bone.
 		</member>

doc/classes/Skeleton3D.xml

@@ -20,9 +20,10 @@
 				Adds a bone, with name [code]name[/code]. [method get_bone_count] will become the bone index.
 			</description>
 		</method>
-		<method name="bone_transform_to_world_transform">
-			<return type="Transform3D" />
-			<argument index="0" name="bone_transform" type="Transform3D" />
+		<method name="add_bone_child">
+			<return type="void" />
+			<argument index="0" name="bone_idx" type="int" />
+			<argument index="1" name="child_bone_idx" type="int" />
 			<description>
 				Takes the given bone pose/transform and converts it to a world transform, relative to the [Skeleton3D] node.
 				This is useful for using the bone transform in calculations with transforms from [Node3D]-based nodes.
@@ -40,6 +41,20 @@
 				Removes the global pose override on all bones in the skeleton.
 			</description>
 		</method>
+		<method name="clear_bones_local_pose_override">
+			<return type="void" />
+			<description>
+				Removes the local pose override on all bones in the skeleton.
+			</description>
+		</method>
+		<method name="execute_modifications">
+			<return type="void" />
+			<argument index="0" name="delta" type="float" />
+			<argument index="1" name="execution_mode" type="int" />
+			<description>
+				Executes all the modifications on the [SkeletonModificationStack3D], if the Skeleton3D has one assigned.
+			</description>
+		</method>
 		<method name="find_bone" qualifiers="const">
 			<return type="int" />
 			<argument index="0" name="name" type="String" />
@@ -47,6 +62,26 @@
 				Returns the bone index that matches [code]name[/code] as its name.
 			</description>
 		</method>
+		<method name="force_update_all_bone_transforms">
+			<return type="void" />
+			<description>
+				Force updates the bone transforms/poses for all bones in the skeleton.
+			</description>
+		</method>
+		<method name="force_update_bone_child_transform">
+			<return type="void" />
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+				Force updates the bone transform for the bone at [code]bone_idx[/code] and all of its children.
+			</description>
+		</method>
+		<method name="get_bone_children">
+			<return type="PackedInt32Array" />
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+				Returns an array containing the bone indexes of all the children node of the passed in bone, [code]bone_idx[/code].
+			</description>
+		</method>
 		<method name="get_bone_count" qualifiers="const">
 			<return type="int" />
 			<description>
@@ -74,6 +109,19 @@
 				Returns the overall transform of the specified bone, with respect to the skeleton, but without any global pose overrides. Being relative to the skeleton frame, this is not the actual "global" transform of the bone.
 			</description>
 		</method>
+		<method name="get_bone_global_pose_override" qualifiers="const">
+			<return type="Transform3D" />
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+			</description>
+		</method>
+		<method name="get_bone_local_pose_override" qualifiers="const">
+			<return type="Transform3D" />
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+				Returns the local pose override transform for [code]bone_idx[/code].
+			</description>
+		</method>
 		<method name="get_bone_name" qualifiers="const">
 			<return type="String" />
 			<argument index="0" name="bone_idx" type="int" />
@@ -96,16 +144,49 @@
 				Returns the pose transform of the specified bone. Pose is applied on top of the custom pose, which is applied on top the rest pose.
 			</description>
 		</method>
-		<method name="get_bone_process_orders">
+		<method name="get_bone_rest" qualifiers="const">
+			<return type="Transform3D" />
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+				Returns the rest transform for a bone [code]bone_idx[/code].
+			</description>
+		</method>
+		<method name="get_modification_stack">
+			<return type="SkeletonModificationStack3D" />
+			<description>
+				Returns the modification stack attached to this skeleton, if one exists.
+			</description>
+		</method>
+		<method name="get_parentless_bones">
 			<return type="PackedInt32Array" />
 			<description>
+				Returns an array with all of the bones that are parentless. Another way to look at this is that it returns the indexes of all the bones that are not dependent or modified by other bones in the Skeleton.
 			</description>
 		</method>
-		<method name="get_bone_rest" qualifiers="const">
+		<method name="global_pose_to_local_pose">
 			<return type="Transform3D" />
 			<argument index="0" name="bone_idx" type="int" />
+			<argument index="1" name="global_pose" type="Transform3D" />
 			<description>
-				Returns the rest transform for a bone [code]bone_idx[/code].
+				Takes the passed-in global pose and converts it to local pose transform.
+				This can be used to easily convert a global pose from [method get_bone_global_pose] to a global transform in [method set_bone_local_pose_override].
+			</description>
+		</method>
+		<method name="global_pose_to_world_transform">
+			<return type="Transform3D" />
+			<argument index="0" name="global_pose" type="Transform3D" />
+			<description>
+				Takes the passed-in global pose and converts it to a world transform.
+				This can be used to easily convert a global pose from [method get_bone_global_pose] to a global transform usable with a node's transform, like [member Node3D.global_transform] for example.
+			</description>
+		</method>
+		<method name="global_pose_z_forward_to_bone_forward">
+			<return type="Basis" />
+			<argument index="0" name="bone_idx" type="int" />
+			<argument index="1" name="basis" type="Basis" />
+			<description>
+				Rotates the given [Basis] so that the forward axis of the Basis is facing in the forward direction of the bone at [code]bone_idx[/code].
+				This is helper function to make using [method Transform3D.looking_at] easier with bone poses.
 			</description>
 		</method>
 		<method name="is_bone_rest_disabled" qualifiers="const">
@@ -115,6 +196,15 @@
 				Returns whether the bone rest for the bone at [code]bone_idx[/code] is disabled.
 			</description>
 		</method>
+		<method name="local_pose_to_global_pose">
+			<return type="Transform3D" />
+			<argument index="0" name="bone_idx" type="int" />
+			<argument index="1" name="local_pose" type="Transform3D" />
+			<description>
+				Converts the passed-in local pose to a global pose relative to the inputted bone, [code]bone_idx[/code].
+				This could be used to convert [method get_bone_pose] for use with the [method set_bone_global_pose_override] function.
+			</description>
+		</method>
 		<method name="localize_rests">
 			<return type="void" />
 			<description>
@@ -158,13 +248,30 @@
 				Binds the given Skin to the Skeleton.
 			</description>
 		</method>
+		<method name="remove_bone_child">
+			<return type="void" />
+			<argument index="0" name="bone_idx" type="int" />
+			<argument index="1" name="child_bone_idx" type="int" />
+			<description>
+				Removes the passed in child bone index, [code]child_bone_idx[/code], from the passed-in bone, [code]bone_idx[/code], if it exists.
+				[b]Note:[/b] This does not remove the child bone, but instead it removes the connection it has to the parent bone.
+			</description>
+		</method>
+		<method name="set_bone_children">
+			<return type="void" />
+			<argument index="0" name="bone_idx" type="int" />
+			<argument index="1" name="bone_children" type="PackedInt32Array" />
+			<description>
+				Sets the children for the passed in bone, [code]bone_idx[/code], to the passed-in array of bone indexes, [code]bone_children[/code].
+			</description>
+		</method>
 		<method name="set_bone_custom_pose">
 			<return type="void" />
 			<argument index="0" name="bone_idx" type="int" />
 			<argument index="1" name="custom_pose" type="Transform3D" />
 			<description>
 				Sets the custom pose transform, [code]custom_pose[/code], for the bone at [code]bone_idx[/code]. This pose is an addition to the bone rest pose.
-				[b]Note[/b]: The pose transform needs to be in bone space. Use [method world_transform_to_bone_transform] to convert a world transform, like one you can get from a [Node3D], to bone space.
+				[b]Note:[/b] The pose transform needs to be in bone space. Use [method world_transform_to_global_pose] to convert a world transform, like one you can get from a [Node3D], to bone space.
 			</description>
 		</method>
 		<method name="set_bone_disable_rest">
@@ -183,8 +290,20 @@
 			<argument index="3" name="persistent" type="bool" default="false" />
 			<description>
 				Sets the global pose transform, [code]pose[/code], for the bone at [code]bone_idx[/code].
-				[code]amount[/code] is the interpolation strength that will be used when applying the pose, and [code]persistent[/code] determines if the applied pose will remain.
-				[b]Note[/b]: The pose transform needs to be in bone space. Use [method world_transform_to_bone_transform] to convert a world transform, like one you can get from a [Node3D], to bone space.
+				[code]amount[/code] is the interpolation strengh that will be used when applying the pose, and [code]persistent[/code] determines if the applied pose will remain.
+				[b]Note:[/b] The pose transform needs to be a global pose! Use [method world_transform_to_global_pose] to convert a world transform, like one you can get from a [Node3D], to a global pose.
+			</description>
+		</method>
+		<method name="set_bone_local_pose_override">
+			<return type="void" />
+			<argument index="0" name="bone_idx" type="int" />
+			<argument index="1" name="pose" type="Transform3D" />
+			<argument index="2" name="amount" type="float" />
+			<argument index="3" name="persistent" type="bool" default="false" />
+			<description>
+				Sets the local pose transform, [code]pose[/code], for the bone at [code]bone_idx[/code].
+				[code]amount[/code] is the interpolation strengh that will be used when applying the pose, and [code]persistent[/code] determines if the applied pose will remain.
+				[b]Note:[/b] The pose transform needs to be a local pose! Use [method global_pose_to_local_pose] to convert a global pose to a local pose.
 			</description>
 		</method>
 		<method name="set_bone_name">
@@ -209,7 +328,7 @@
 			<argument index="1" name="pose" type="Transform3D" />
 			<description>
 				Sets the pose transform for bone [code]bone_idx[/code].
-				[b]Note[/b]: The pose transform needs to be in bone space. Use [method world_transform_to_bone_transform] to convert a world transform, like one you can get from a [Node3D], to bone space.
+				[b]Note:[/b] The pose transform needs to be in bone space. Use [method world_transform_to_global_pose] to convert a world transform, like one you can get from a [Node3D], to bone space.
 			</description>
 		</method>
 		<method name="set_bone_rest">
@@ -220,6 +339,13 @@
 				Sets the rest transform for bone [code]bone_idx[/code].
 			</description>
 		</method>
+		<method name="set_modification_stack">
+			<return type="void" />
+			<argument index="0" name="modification_stack" type="SkeletonModificationStack3D" />
+			<description>
+				Sets the modification stack for this skeleton to the passed-in modification stack, [code]modification_stack[/code].
+			</description>
+		</method>
 		<method name="unparent_bone_and_rest">
 			<return type="void" />
 			<argument index="0" name="bone_idx" type="int" />
@@ -227,12 +353,12 @@
 				Unparents the bone at [code]bone_idx[/code] and sets its rest position to that of its parent prior to being reset.
 			</description>
 		</method>
-		<method name="world_transform_to_bone_transform">
+		<method name="world_transform_to_global_pose">
 			<return type="Transform3D" />
 			<argument index="0" name="world_transform" type="Transform3D" />
 			<description>
-				Takes the given world transform, relative to the [Skeleton3D], and converts it to a bone pose/transform.
-				This is useful for using setting bone poses using transforms from [Node3D]-based nodes.
+				Takes the passed-in global transform and converts it to a global pose.
+				This can be used to easily convert a global transform from [member Node3D.global_transform] to a global pose usable with [method set_bone_global_pose_override], for example.
 			</description>
 		</method>
 	</methods>
@@ -241,6 +367,12 @@
 		</member>
 	</members>
 	<signals>
+		<signal name="bone_pose_changed">
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+				This signal is emitted when one of the bones in the Skeleton3D node have changed their pose. This is used to inform nodes that rely on bone positions that one of the bones in the Skeleton3D have changed their transform/pose.
+			</description>
+		</signal>
 		<signal name="pose_updated">
 			<description>
 			</description>

doc/classes/SkeletonModification3D.xml

@@ -0,0 +1,68 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="SkeletonModification3D" inherits="Resource" version="4.0">
+	<brief_description>
+		A resource that operates on bones in a [Skeleton3D].
+	</brief_description>
+	<description>
+		This resource provides an interface that can be expanded so code that operates on bones in a [Skeleton3D] can be mixed and matched together to create complex interactions.
+		This is used to provide Godot with a flexible and powerful Inverse Kinematics solution that can be adapted for many different uses.
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="_execute" qualifiers="virtual">
+			<return type="void" />
+			<argument index="0" name="delta" type="float" />
+			<description>
+				Executes the given modification. This is where the modification performs whatever function it is designed to do.
+			</description>
+		</method>
+		<method name="_setup_modification" qualifiers="virtual">
+			<return type="void" />
+			<argument index="0" name="modification_stack" type="SkeletonModificationStack3D" />
+			<description>
+				Sets up the modification so it can be executed. This function should be called automatically by the [SkeletonModificationStack3D] containing this modification.
+				If you need to initialize a modification before use, this is the place to do it!
+			</description>
+		</method>
+		<method name="clamp_angle">
+			<return type="float" />
+			<argument index="0" name="angle" type="float" />
+			<argument index="1" name="min" type="float" />
+			<argument index="2" name="max" type="float" />
+			<argument index="3" name="invert" type="bool" />
+			<description>
+				Takes a angle and clamps it so it is within the passed-in [code]min[/code] and [code]max[/code] range. [code]invert[/code] will inversely clamp the angle, clamping it to the range outside of the given bounds.
+			</description>
+		</method>
+		<method name="get_is_setup" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns whether this modification has been successfully setup or not.
+			</description>
+		</method>
+		<method name="get_modification_stack">
+			<return type="SkeletonModificationStack3D" />
+			<description>
+				Returns the [SkeletonModificationStack3D] that this modification is bound to. Through the modification stack, you can access the Skeleton3D the modification is operating on.
+			</description>
+		</method>
+		<method name="set_is_setup">
+			<return type="void" />
+			<argument index="0" name="is_setup" type="bool" />
+			<description>
+				Manually allows you to set the setup state of the modification. This function should only rarely be used, as the [SkeletonModificationStack3D] the modification is bound to should handle setting the modification up.
+			</description>
+		</method>
+	</methods>
+	<members>
+		<member name="enabled" type="bool" setter="set_enabled" getter="get_enabled" default="true">
+			When true, the modification's [method _execute] function will be called by the [SkeletonModificationStack3D].
+		</member>
+		<member name="execution_mode" type="int" setter="set_execution_mode" getter="get_execution_mode" default="0">
+			The execution mode for the modification. This tells the modification stack when to execute the modification. Some modifications have settings that are only availible in certain execution modes.
+		</member>
+	</members>
+	<constants>
+	</constants>
+</class>

doc/classes/SkeletonModification3DCCDIK.xml

@@ -0,0 +1,138 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="SkeletonModification3DCCDIK" inherits="SkeletonModification3D" version="4.0">
+	<brief_description>
+		A modification that uses CCDIK to manipulate a series of bones to reach a target.
+	</brief_description>
+	<description>
+		This [SkeletonModification3D] uses an algorithm called [b]C[/b]yclic [b]C[/b]oordinate [b]D[/b]escent [b]I[/b]nverse [b]K[/b]inematics, or CCDIK, to maniuplate a chain of bones in a Skeleton so it reaches a defined target.
+		CCDIK works by rotating a set of bones, typically called a "bone chain", on a single axis. Each bone is rotated to face the target from the tip (by default), which over a chain of bones allow it to rotate properly to reach the target. Because the bones only rotate on a single axis, CCDIK [i]can[/i] look more robotic than other IK solvers.
+		[b]Note:[/b] The CCDIK modifier has [code]ccdik_joints[/code], which are the data objects that hold the data for each joint in the CCDIK chain. This is different from a bone! CCDIK joints hold the data needed for each bone in the bone chain used by CCDIK.
+		CCDIK also fully supports angle constraints, allowing for more control over how a solution is met.
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="get_ccdik_joint_bone_index" qualifiers="const">
+			<return type="int" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the bone index of the bone assigned to the CCDIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_ccdik_joint_bone_name" qualifiers="const">
+			<return type="String" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the name of the bone that is assigned to the CCDIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_ccdik_joint_ccdik_axis" qualifiers="const">
+			<return type="int" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the integer representing the joint axis of the CCDIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_ccdik_joint_constraint_angle_max" qualifiers="const">
+			<return type="float" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the maximum angle constraint for the joint at [code]joint_idx[/code]. [b]Note:[/b] This angle is in degrees!
+			</description>
+		</method>
+		<method name="get_ccdik_joint_constraint_angle_min" qualifiers="const">
+			<return type="float" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the minimum angle constraint for the joint at [code]joint_idx[/code]. [b]Note:[/b] This angle is in degrees!
+			</description>
+		</method>
+		<method name="get_ccdik_joint_constraint_invert" qualifiers="const">
+			<return type="bool" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns whether the CCDIK joint at [code]joint_idx[/code] uses an inverted joint constraint. See [method set_ccdik_joint_constraint_invert] for details.
+			</description>
+		</method>
+		<method name="get_ccdik_joint_enable_joint_constraint" qualifiers="const">
+			<return type="bool" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Enables angle constraints to the CCDIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="set_ccdik_joint_bone_index">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="bone_index" type="int" />
+			<description>
+				Sets the bone index, [code]bone_index[/code], of the CCDIK joint at [code]joint_idx[/code]. When possible, this will also update the [code]bone_name[/code] of the CCDIK joint based on data provided by the linked skeleton.
+			</description>
+		</method>
+		<method name="set_ccdik_joint_bone_name">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="bone_name" type="String" />
+			<description>
+				Sets the bone name, [code]bone_name[/code], of the CCDIK joint at [code]joint_idx[/code]. When possible, this will also update the [code]bone_index[/code] of the CCDIK joint based on data provided by the linked skeleton.
+			</description>
+		</method>
+		<method name="set_ccdik_joint_ccdik_axis">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="axis" type="int" />
+			<description>
+				Sets the joint axis of the CCDIK joint at [code]joint_idx[/code] to the passed-in joint axis, [code]axis[/code].
+			</description>
+		</method>
+		<method name="set_ccdik_joint_constraint_angle_max">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="max_angle" type="float" />
+			<description>
+				Sets the maximum angle constraint for the joint at [code]joint_idx[/code]. [b]Note:[/b] This angle must be in radians!
+			</description>
+		</method>
+		<method name="set_ccdik_joint_constraint_angle_min">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="min_angle" type="float" />
+			<description>
+				Sets the minimum angle constraint for the joint at [code]joint_idx[/code]. [b]Note:[/b] This angle must be in radians!
+			</description>
+		</method>
+		<method name="set_ccdik_joint_constraint_invert">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="invert" type="bool" />
+			<description>
+				Sets whether the CCDIK joint at [code]joint_idx[/code] uses an inverted joint constraint.
+				An inverted joint constraint only constraints the CCDIK joint to the angles [i]outside of[/i] the inputted minimum and maximum angles. For this reason, it is referred to as an inverted joint constraint, as it constraints the joint to the outside of the inputted values.
+			</description>
+		</method>
+		<method name="set_ccdik_joint_enable_joint_constraint">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="enable" type="bool" />
+			<description>
+				Sets whether joint constraints are enabled for the CCDIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+	</methods>
+	<members>
+		<member name="ccdik_data_chain_length" type="int" setter="set_ccdik_data_chain_length" getter="get_ccdik_data_chain_length" default="0">
+			The amount of CCDIK joints in the CCDIK modification.
+		</member>
+		<member name="high_quality_solve" type="bool" setter="set_use_high_quality_solve" getter="get_use_high_quality_solve" default="true">
+			When true, the CCDIK algorithm will perform a higher quality solve that returns more natural results. A high quality solve requires more computation power to solve though, and therefore can be disabled to save performance.
+		</member>
+		<member name="target_nodepath" type="NodePath" setter="set_target_node" getter="get_target_node" default="NodePath(&quot;&quot;)">
+			The NodePath to the node that is the target for the CCDIK modification. This node is what the CCDIK chain will attempt to rotate the bone chain to.
+		</member>
+		<member name="tip_nodepath" type="NodePath" setter="set_tip_node" getter="get_tip_node" default="NodePath(&quot;&quot;)">
+			The end position of the CCDIK chain. Typically, this should be a child of a [BoneAttachment3D] node attached to the final bone in the CCDIK chain, where the child node is offset so it is at the end of the final bone.
+		</member>
+	</members>
+	<constants>
+	</constants>
+</class>

doc/classes/SkeletonModification3DFABRIK.xml

@@ -0,0 +1,163 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="SkeletonModification3DFABRIK" inherits="SkeletonModification3D" version="4.0">
+	<brief_description>
+		A modification that uses FABRIK to manipulate a series of bones to reach a target.
+	</brief_description>
+	<description>
+		This [SkeletonModification3D] uses an algorithm called [b]F[/b]orward [b]A[/b]nd [b]B[/b]ackward [b]R[/b]eaching [b]I[/b]nverse [b]K[/b]inematics, or FABRIK, to rotate a bone chain so that it reaches a target.
+		FABRIK works by knowing the positions and lengths of a series of bones, typically called a "bone chain". It first starts by running a forward pass, which places the final bone at the target's position. Then all other bones are moved towards the tip bone, so they stay at the defined bone length away. Then a backwards pass is performed, where the root/first bone in the FABRIK chain is placed back at the origin. then all other bones are moved so they stay at the defined bone length away. This positions the bone chain so that it reaches the target when possible, but all of the bones stay the correct length away from each other.
+		Because of how FABRIK works, it often gives more natural results than those seen in [SkeletonModification3DCCDIK], though FABRIK currently does not support joint constraints.
+		[b]Note:[/b] The FABRIK modifier has [code]fabrik_joints[/code], which are the data objects that hold the data for each joint in the FABRIK chain. This is different from a bone! FABRIK joints hold the data needed for each bone in the bone chain used by FABRIK.
+		To help control how the FABRIK joints move, a magnet vector can be passed, which can nudge the bones in a certain direction prior to solving, giving a level of control over the final result.
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="fabrik_joint_auto_calculate_length">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Will attempt to automatically calculate the length of the bone assigned to the FABRIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_fabrik_joint_auto_calculate_length" qualifiers="const">
+			<return type="bool" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns a boolean that indiciates whether this modification will attempt to autocalculate the length of the bone assigned to the FABRIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_fabrik_joint_bone_index" qualifiers="const">
+			<return type="int" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the bone index of the bone assigned to the FABRIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_fabrik_joint_bone_name" qualifiers="const">
+			<return type="String" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the name of the bone that is assigned to the FABRIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_fabrik_joint_length" qualifiers="const">
+			<return type="float" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the length of the FABRIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_fabrik_joint_magnet" qualifiers="const">
+			<return type="Vector3" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the magnet vector of the FABRIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_fabrik_joint_tip_node" qualifiers="const">
+			<return type="NodePath" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the [Node3D]-based node placed at the tip of the FABRIK joint at [code]joint_idx[/code], if one has been set.
+			</description>
+		</method>
+		<method name="get_fabrik_joint_use_target_basis" qualifiers="const">
+			<return type="bool" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns a boolean indiciating whether the FABRIK joint uses the target's [Basis] for its rotation.
+				[b]Note:[/b] this option is only available for the final bone in the FABRIK chain, with this setting being ignored for all other bones.
+			</description>
+		</method>
+		<method name="get_fabrik_joint_use_tip_node" qualifiers="const">
+			<return type="bool" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Sets the [Node3D]-based node that will be used as the tip of the FABRIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="set_fabrik_joint_auto_calculate_length">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="auto_calculate_length" type="bool" />
+			<description>
+				When [code]true[/code], this modification will attempt to automatically calculate the length of the bone for the FABRIK joint at [code]joint_idx[/code]. It does this by either using the tip node assigned, if there is one assigned, or the distance the of the bone's children, if the bone has any. If the bone has no children and no tip node is assigned, then the modification [b]cannot[/b] autocalculate the joint's length. In this case, the joint length should be entered manually or a tip node assigned.
+			</description>
+		</method>
+		<method name="set_fabrik_joint_bone_index">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="bone_index" type="int" />
+			<description>
+				Sets the bone index, [code]bone_index[/code], of the FABRIK joint at [code]joint_idx[/code]. When possible, this will also update the [code]bone_name[/code] of the FABRIK joint based on data provided by the [Skeleton3D].
+			</description>
+		</method>
+		<method name="set_fabrik_joint_bone_name">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="bone_name" type="String" />
+			<description>
+				Sets the bone name, [code]bone_name[/code], of the FABRIK joint at [code]joint_idx[/code]. When possible, this will also update the [code]bone_index[/code] of the FABRIK joint based on data provided by the [Skeleton3D].
+			</description>
+		</method>
+		<method name="set_fabrik_joint_length">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="length" type="float" />
+			<description>
+				Sets the joint length, [code]length[/code], of the FABRIK joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="set_fabrik_joint_magnet">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="magnet_position" type="Vector3" />
+			<description>
+				Sets the magenet position to [code]magnet_position[/code] for the joint at [code]joint_idx[/code]. The magnet position is used to nudge the joint in that direction when solving, which gives some control over how that joint will bend when being solved.
+			</description>
+		</method>
+		<method name="set_fabrik_joint_tip_node">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="tip_node" type="NodePath" />
+			<description>
+				Sets the nodepath of the FARIK joint at [code]joint_idx[/code] to [code]tip_node[/code]. The tip node is used to calculate the length of the FABRIK joint when set to automatically calculate joint length.
+				[b]Note:[/b] The tip node should generally be a child node of a [BoneAttachment3D] node attached to the bone that this FABRIK joint operates on, with the child node being offset so it is at the end of the bone.
+			</description>
+		</method>
+		<method name="set_fabrik_joint_use_target_basis">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="use_target_basis" type="bool" />
+			<description>
+				Sets whether the FABRIK joint at [code]joint_idx[/code] uses the target's [Basis] for its rotation.
+				[b]Note:[/b] this option is only available for the final bone in the FABRIK chain, with this setting being ignored for all other bones.
+			</description>
+		</method>
+		<method name="set_fabrik_joint_use_tip_node">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="use_tip_node" type="bool" />
+			<description>
+				Sets whether the tip node should be used when autocalculating the joint length for the FABRIK joint at [code]joint_idx[/code]. This will only work if there is a node assigned to the tip nodepath for this joint.
+			</description>
+		</method>
+	</methods>
+	<members>
+		<member name="chain_max_iterations" type="int" setter="set_chain_max_iterations" getter="get_chain_max_iterations" default="10">
+			The number of times FABRIK will try to solve each time the [code]execute[/code] function is called. Setting this value to a lower number will be result in better performance, but this can also result in harsher movements and slower solves.
+		</member>
+		<member name="chain_tolerance" type="float" setter="set_chain_tolerance" getter="get_chain_tolerance" default="0.01">
+			The minimum distance the target has to be from the tip of the final bone in the bone chain. Setting this value to a higher number allows for greater performance, but less accurate solves.
+		</member>
+		<member name="fabrik_data_chain_length" type="int" setter="set_fabrik_data_chain_length" getter="get_fabrik_data_chain_length" default="0">
+			The amount of FABRIK joints in the FABRIK modification.
+		</member>
+		<member name="target_nodepath" type="NodePath" setter="set_target_node" getter="get_target_node" default="NodePath(&quot;&quot;)">
+			The NodePath to the node that is the target for the FABRIK modification. This node is what the FABRIK chain will attempt to rotate the bone chain to.
+		</member>
+	</members>
+	<constants>
+	</constants>
+</class>

doc/classes/SkeletonModification3DJiggle.xml

@@ -0,0 +1,201 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="SkeletonModification3DJiggle" inherits="SkeletonModification3D" version="4.0">
+	<brief_description>
+		A modification that jiggles bones as they move towards a target.
+	</brief_description>
+	<description>
+		This modification moves a series of bones, typically called a bone chain, towards a target. What makes this modification special is that it calculates the velocity and acceleration for each bone in the bone chain, and runs a very light physics-like calculation using the inputted values. This allows the bones to overshoot the target and "jiggle" around. It can be configured to act more like a spring, or sway around like cloth might.
+		This modification is useful for adding additional motion to things like hair, the edges of clothing, and more. It has several settings to that allow control over how the joint moves when the target moves.
+		[b]Note:[/b] The Jiggle modifier has [code]jiggle_joints[/code], which are the data objects that hold the data for each joint in the Jiggle chain. This is different from a bone! Jiggle joints hold the data needed for each bone in the bone chain used by the Jiggle modification.
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="get_collision_mask" qualifiers="const">
+			<return type="int" />
+			<description>
+				Returns the collision mask that the Jiggle modifier will take into account when performing physics calculations.
+			</description>
+		</method>
+		<method name="get_jiggle_joint_bone_index" qualifiers="const">
+			<return type="int" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the bone index of the bone assigned to the Jiggle joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_jiggle_joint_bone_name" qualifiers="const">
+			<return type="String" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the name of the bone that is assigned to the Jiggle joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_jiggle_joint_damping" qualifiers="const">
+			<return type="float" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the amount of dampening of the Jiggle joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_jiggle_joint_gravity" qualifiers="const">
+			<return type="Vector3" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns a [Vector3] representign the amount of gravity the Jiggle joint at [code]joint_idx[/code] is influenced by.
+			</description>
+		</method>
+		<method name="get_jiggle_joint_mass" qualifiers="const">
+			<return type="float" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the amount of mass of the Jiggle joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_jiggle_joint_override" qualifiers="const">
+			<return type="bool" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns a boolean that indiciates whether the joint at [code]joint_idx[/code] is overriding the default jiggle joint data defined in the modification.
+			</description>
+		</method>
+		<method name="get_jiggle_joint_roll" qualifiers="const">
+			<return type="float" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the amount of roll/twist applied to the bone that the Jiggle joint is applied to.
+			</description>
+		</method>
+		<method name="get_jiggle_joint_stiffness" qualifiers="const">
+			<return type="float" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns the stiffness of the Jiggle joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="get_jiggle_joint_use_gravity" qualifiers="const">
+			<return type="bool" />
+			<argument index="0" name="joint_idx" type="int" />
+			<description>
+				Returns a boolean that indiciates whether the joint at [code]joint_idx[/code] is using gravity or not.
+			</description>
+		</method>
+		<method name="get_use_colliders" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns whether the Jiggle modifier is taking physics colliders into account when solving.
+			</description>
+		</method>
+		<method name="set_collision_mask">
+			<return type="void" />
+			<argument index="0" name="mask" type="int" />
+			<description>
+				Sets the collision mask that the Jiggle modifier takes into account when performing physics calculations.
+			</description>
+		</method>
+		<method name="set_jiggle_joint_bone_index">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="bone_idx" type="int" />
+			<description>
+				Sets the bone index, [code]bone_index[/code], of the Jiggle joint at [code]joint_idx[/code]. When possible, this will also update the [code]bone_name[/code] of the Jiggle joint based on data provided by the [Skeleton3D].
+			</description>
+		</method>
+		<method name="set_jiggle_joint_bone_name">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="name" type="String" />
+			<description>
+				Sets the bone name, [code]bone_name[/code], of the Jiggle joint at [code]joint_idx[/code]. When possible, this will also update the [code]bone_index[/code] of the Jiggle joint based on data provided by the [Skeleton3D].
+			</description>
+		</method>
+		<method name="set_jiggle_joint_damping">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="damping" type="float" />
+			<description>
+				Sets the amount of dampening of the Jiggle joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="set_jiggle_joint_gravity">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="gravity" type="Vector3" />
+			<description>
+				Sets the gravity vector of the Jiggle joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="set_jiggle_joint_mass">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="mass" type="float" />
+			<description>
+				Sets the of mass of the Jiggle joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="set_jiggle_joint_override">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="override" type="bool" />
+			<description>
+				Sets whether the Jiggle joint at [code]joint_idx[/code] should override the default Jiggle joint settings. Setting this to true will make the joint use its own settings rather than the default ones attached to the modification.
+			</description>
+		</method>
+		<method name="set_jiggle_joint_roll">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="roll" type="float" />
+			<description>
+				Sets the amount of roll/twist on the bone the Jiggle joint is attached to.
+			</description>
+		</method>
+		<method name="set_jiggle_joint_stiffness">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="stiffness" type="float" />
+			<description>
+				Sets the of stiffness of the Jiggle joint at [code]joint_idx[/code].
+			</description>
+		</method>
+		<method name="set_jiggle_joint_use_gravity">
+			<return type="void" />
+			<argument index="0" name="joint_idx" type="int" />
+			<argument index="1" name="use_gravity" type="bool" />
+			<description>
+				Sets whether the Jiggle joint at [code]joint_idx[/code] should use gravity.
+			</description>
+		</method>
+		<method name="set_use_colliders">
+			<return type="void" />
+			<argument index="0" name="use_colliders" type="bool" />
+			<description>
+				When [code]true[/code], the Jiggle modifier will use raycasting to prevent the Jiggle joints from rotating themselves into collision objects when solving.
+			</description>
+		</method>
+	</methods>
+	<members>
+		<member name="damping" type="float" setter="set_damping" getter="get_damping" default="0.75">
+			The default amount of dampening applied to the Jiggle joints, if they are not overriden. Higher values lead to more of the calculated velocity being applied.
+		</member>
+		<member name="gravity" type="Vector3" setter="set_gravity" getter="get_gravity" default="Vector3(0, -6, 0)">
+			The default amount of gravity applied to the Jiggle joints, if they are not overriden.
+		</member>
+		<member name="jiggle_data_chain_length" type="int" setter="set_jiggle_data_chain_length" getter="get_jiggle_data_chain_length" default="0">
+			The amount of Jiggle joints in the Jiggle modification.
+		</member>
+		<member name="mass" type="float" setter="set_mass" getter="get_mass" default="0.75">
+			The default amount of mass assigned to the Jiggle joints, if they are not overriden. Higher values lead to faster movements and more overshooting.
+		</member>
+		<member name="stiffness" type="float" setter="set_stiffness" getter="get_stiffness" default="3.0">
+			The default amount of stiffness assigned to the Jiggle joints, if they are not overriden. Higher values act more like springs, quickly moving into the correct position.
+		</member>
+		<member name="target_nodepath" type="NodePath" setter="set_target_node" getter="get_target_node" default="NodePath(&quot;&quot;)">
+			The NodePath to the node that is the target for the Jiggle modification. This node is what the Jiggle chain will attempt to rotate the bone chain to.
+		</member>
+		<member name="use_gravity" type="bool" setter="set_use_gravity" getter="get_use_gravity" default="false">
+			Whether the gravity vector, [member gravity], should be applied to the Jiggle joints, assuming they are not overriding the default settings.
+		</member>
+	</members>
+	<constants>
+	</constants>
+</class>

doc/classes/SkeletonModification3DLookAt.xml

@@ -0,0 +1,66 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="SkeletonModification3DLookAt" inherits="SkeletonModification3D" version="4.0">
+	<brief_description>
+		A modification that rotates a bone to look at a target.
+	</brief_description>
+	<description>
+		This [SkeletonModification3D] rotates a bone to look a target. This is extremely helpful for moving character's heads to look at the player, rotating a turret to look at a target, or any other case where you want to make a bone rotate towards something quickly and easily.
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="get_additional_rotation" qualifiers="const">
+			<return type="Vector3" />
+			<description>
+				Returns the amount of extra rotation that is applied to the bone after the LookAt modification executes.
+			</description>
+		</method>
+		<method name="get_lock_rotation_plane" qualifiers="const">
+			<return type="int" />
+			<description>
+				Returns the plane that the LookAt modification is limiting rotation to.
+			</description>
+		</method>
+		<method name="get_lock_rotation_to_plane" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns whether the LookAt modification is limiting rotation to a single plane in 3D space.
+			</description>
+		</method>
+		<method name="set_additional_rotation">
+			<return type="void" />
+			<argument index="0" name="additional_rotation" type="Vector3" />
+			<description>
+				Sets the amount of extra rotation to be applied after the LookAt modification executes. This allows you to adjust the finished result.
+			</description>
+		</method>
+		<method name="set_lock_rotation_plane">
+			<return type="void" />
+			<argument index="0" name="plane" type="int" />
+			<description>
+			</description>
+		</method>
+		<method name="set_lock_rotation_to_plane">
+			<return type="void" />
+			<argument index="0" name="lock_to_plane" type="bool" />
+			<description>
+				When [code]true[/code], the LookAt modification will limit its rotation to a single plane in 3D space. The plane used can be configured using the [code]set_lock_rotation_plane[/code] function.
+			</description>
+		</method>
+	</methods>
+	<members>
+		<member name="bone_index" type="int" setter="set_bone_index" getter="get_bone_index" default="-2">
+			The bone index of the bone that should be operated on by this modification.
+			When possible, this will also update the [member bone_name] based on data provided by the [Skeleton3D].
+		</member>
+		<member name="bone_name" type="String" setter="set_bone_name" getter="get_bone_name" default="&quot;&quot;">
+			The name of the bone that should be operated on by this modification.
+			When possible, this will also update the [member bone_index] based on data provided by the [Skeleton3D].
+		</member>
+		<member name="target_nodepath" type="NodePath" setter="set_target_node" getter="get_target_node" default="NodePath(&quot;&quot;)">
+			The NodePath to the node that is the target for the modification.
+		</member>
+	</members>
+	<constants>
+	</constants>
+</class>

doc/classes/SkeletonModification3DStackHolder.xml

@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="SkeletonModification3DStackHolder" inherits="SkeletonModification3D" version="4.0">
+	<brief_description>
+		A modification that holds and executes a [SkeletonModificationStack3D].
+	</brief_description>
+	<description>
+		This [SkeletonModification3D] holds a reference to a [SkeletonModificationStack3D], allowing you to use multiple modification stacks on a single [Skeleton3D].
+		[b]Note[/b]: The modifications in the held [SkeletonModificationStack3D] will only be executed if their execution mode matches the execution mode of the SkeletonModification3DStackHolder.
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="get_held_modification_stack" qualifiers="const">
+			<return type="SkeletonModificationStack3D" />
+			<description>
+				Returns the [SkeletonModificationStack3D] that this modification is holding.
+			</description>
+		</method>
+		<method name="set_held_modification_stack">
+			<return type="void" />
+			<argument index="0" name="held_modification_stack" type="SkeletonModificationStack3D" />
+			<description>
+				Sets the [SkeletonModificationStack3D] that this modification is holding. This modification stack will then be executed when this modification is executed.
+			</description>
+		</method>
+	</methods>
+	<constants>
+	</constants>
+</class>

doc/classes/SkeletonModification3DTwoBoneIK.xml

@@ -0,0 +1,193 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="SkeletonModification3DTwoBoneIK" inherits="SkeletonModification3D" version="4.0">
+	<brief_description>
+		A modification that moves two bones to reach the target.
+	</brief_description>
+	<description>
+		This [SkeletonModification3D] uses an algorithm typically called TwoBoneIK. This algorithm works by leveraging the law of cosigns and the lengths of the bones to figure out what rotation the bones currently have, and what rotation they need to make a complete triangle, where the first bone, the second bone, and the target form the three verticies of the triangle. Because the algorithm works by making a triangle, it can only opperate on two bones.
+		TwoBoneIK is great for arms, legs, and really any joints that can be represented by just two bones that bend to reach a target. This solver is more lightweight than [SkeletonModification3DFABRIK], but gives similar, natural looking results.
+		A [Node3D]-based node can be used to define the pole, or bend direction, allowing control over which direction the joint takes when bending to reach the target when the target is within reach.
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="get_auto_calculate_joint_length" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns whether the TwoBoneIK modification will attempt to autocalculate the lengths of the two bones.
+			</description>
+		</method>
+		<method name="get_joint_one_bone_idx" qualifiers="const">
+			<return type="int" />
+			<description>
+				Returns the bone index of the first bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="get_joint_one_bone_name" qualifiers="const">
+			<return type="String" />
+			<description>
+				Returns the name of the first bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="get_joint_one_length" qualifiers="const">
+			<return type="float" />
+			<description>
+				Returns the length of the first bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="get_joint_one_roll" qualifiers="const">
+			<return type="float" />
+			<description>
+				Returns the amount of roll/twist applied to the first bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="get_joint_two_bone_idx" qualifiers="const">
+			<return type="int" />
+			<description>
+				Returns the bone index of the second bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="get_joint_two_bone_name" qualifiers="const">
+			<return type="String" />
+			<description>
+				Returns the name of the second bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="get_joint_two_length" qualifiers="const">
+			<return type="float" />
+			<description>
+				Returns the length of the second bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="get_joint_two_roll" qualifiers="const">
+			<return type="float" />
+			<description>
+				Returns the amount of roll/twist applied to the second bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="get_pole_node" qualifiers="const">
+			<return type="NodePath" />
+			<description>
+				Returns the node that is being used as the pole node for the TwoBoneIK modification, if a pole node has been set.
+			</description>
+		</method>
+		<method name="get_tip_node" qualifiers="const">
+			<return type="NodePath" />
+			<description>
+				Returns the node that is being used to calculate the tip position of the second bone in the TwoBoneIK modification, if a tip node has been set.
+			</description>
+		</method>
+		<method name="get_use_pole_node" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns whether the TwoBoneIK modification will attempt to use the pole node to figure out which direction to bend, if a pole node has been set.
+			</description>
+		</method>
+		<method name="get_use_tip_node" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns whether the TwoBoneIK modification will attempt to use the tip node to figure out the length and position of the tip of the second bone.
+			</description>
+		</method>
+		<method name="set_auto_calculate_joint_length">
+			<return type="void" />
+			<argument index="0" name="auto_calculate_joint_length" type="bool" />
+			<description>
+				If true, the TwoBoneIK modification will attempt to autocalculate the lengths of the bones being used. The first bone will be calculated by using the distance from the origin of the first bone to the origin of the second bone.
+				The second bone will be calculated either using the tip node if that setting is enabled, or by using the distances of the second bone's children. If the tip node is not enabled and the bone has no children, then the length cannot be autocalculated. In this case, the length will either have to be manually inputted or a tip node used to calculate the length.
+			</description>
+		</method>
+		<method name="set_joint_one_bone_idx">
+			<return type="void" />
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+				Sets the bone index, [code]bone_index[/code], of the first bone. When possible, this will also update the [code]bone_name[/code] of the first bone based on data provided by the [Skeleton3D].
+			</description>
+		</method>
+		<method name="set_joint_one_bone_name">
+			<return type="void" />
+			<argument index="0" name="bone_name" type="String" />
+			<description>
+				Sets the bone name, [code]bone_name[/code], of the first bone. When possible, this will also update the [code]bone_index[/code] of the first bone based on data provided by the [Skeleton3D].
+			</description>
+		</method>
+		<method name="set_joint_one_length">
+			<return type="void" />
+			<argument index="0" name="bone_length" type="float" />
+			<description>
+				Sets the length of the first bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="set_joint_one_roll">
+			<return type="void" />
+			<argument index="0" name="roll" type="float" />
+			<description>
+				Sets the amount of roll/twist applied to the first bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="set_joint_two_bone_idx">
+			<return type="void" />
+			<argument index="0" name="bone_idx" type="int" />
+			<description>
+				Sets the bone index, [code]bone_index[/code], of the second bone. When possible, this will also update the [code]bone_name[/code] of the second bone based on data provided by the [Skeleton3D].
+			</description>
+		</method>
+		<method name="set_joint_two_bone_name">
+			<return type="void" />
+			<argument index="0" name="bone_name" type="String" />
+			<description>
+				Sets the bone name, [code]bone_name[/code], of the second bone. When possible, this will also update the [code]bone_index[/code] of the second bone based on data provided by the [Skeleton3D].
+			</description>
+		</method>
+		<method name="set_joint_two_length">
+			<return type="void" />
+			<argument index="0" name="bone_length" type="float" />
+			<description>
+				Sets the length of the second bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="set_joint_two_roll">
+			<return type="void" />
+			<argument index="0" name="roll" type="float" />
+			<description>
+				Sets the amount of roll/twist applied to the second bone in the TwoBoneIK modification.
+			</description>
+		</method>
+		<method name="set_pole_node">
+			<return type="void" />
+			<argument index="0" name="pole_nodepath" type="NodePath" />
+			<description>
+				Sets the node to be used as the for the pole of the TwoBoneIK. When a node is set and the modification is set to use the pole node, the TwoBoneIK modification will bend the nodes in the direction towards this node when the bones need to bend.
+			</description>
+		</method>
+		<method name="set_tip_node">
+			<return type="void" />
+			<argument index="0" name="tip_nodepath" type="NodePath" />
+			<description>
+				Sets the node to be used as the tip for the second bone. This is used to calculate the length and position of the end of the second bone in the TwoBoneIK modification.
+				[b]Note:[/b] The tip node should generally be a child node of a [BoneAttachment3D] node attached to the second bone, with the child node being offset so it is at the end of the bone.
+			</description>
+		</method>
+		<method name="set_use_pole_node">
+			<return type="void" />
+			<argument index="0" name="use_pole_node" type="bool" />
+			<description>
+				When [code]true[/code], the TwoBoneIK modification will bend the bones towards the pole node, if one has been set. This gives control over the direction the TwoBoneIK solver will bend, which is helpful for joints like elbows that only bend in certain directions.
+			</description>
+		</method>
+		<method name="set_use_tip_node">
+			<return type="void" />
+			<argument index="0" name="use_tip_node" type="bool" />
+			<description>
+				When [code]true[/code], the TwoBoneIK modification will use the tip node to calculate the distance and position of the end/tip of the second bone. This is the most stable solution for knowing the tip position and length of the second bone.
+			</description>
+		</method>
+	</methods>
+	<members>
+		<member name="target_nodepath" type="NodePath" setter="set_target_node" getter="get_target_node" default="NodePath(&quot;&quot;)">
+			The NodePath to the node that is the target for the TwoBoneIK modification. This node is what the modification will attempt to rotate the bones to reach.
+		</member>
+	</members>
+	<constants>
+	</constants>
+</class>

doc/classes/SkeletonModificationStack3D.xml

@@ -0,0 +1,90 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="SkeletonModificationStack3D" inherits="Resource" version="4.0">
+	<brief_description>
+		A resource that holds a stack of [SkeletonModification3D]s.
+	</brief_description>
+	<description>
+		This resource is used by the Skeleton and holds a stack of [SkeletonModification3D]s. The SkeletonModificationStack3D controls the order of the modifications, which controls how they are applied. Modification order is especially important for full-body IK setups, as you need to execute the modifications in the correct order to get the desired results. For example, you want to execute a modification on the spine [i]before[/i] the arms on a humanoid skeleton.
+		Additionally, the SkeletonModificationStack3D also controls how strongly the modifications are applied to the [Skeleton3D] node.
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="add_modification">
+			<return type="void" />
+			<argument index="0" name="modification" type="SkeletonModification3D" />
+			<description>
+				Adds the passed-in [SkeletonModification3D] to the stack.
+			</description>
+		</method>
+		<method name="delete_modification">
+			<return type="void" />
+			<argument index="0" name="mod_idx" type="int" />
+			<description>
+				Deletes the [SkeletonModification3D] at the index position [code]mod_idx[/code], if it exists.
+			</description>
+		</method>
+		<method name="enable_all_modifications">
+			<return type="void" />
+			<argument index="0" name="enabled" type="bool" />
+			<description>
+				Enables all [SkeletonModification3D]s in the stack.
+			</description>
+		</method>
+		<method name="execute">
+			<return type="void" />
+			<argument index="0" name="delta" type="float" />
+			<argument index="1" name="execution_mode" type="int" />
+			<description>
+				Executes all of the [SkeletonModification3D]s in the stack that use the same execution mode as the passed-in [code]execution_mode[/code], starting from index [code]0[/code] to [member modification_count].
+				[b]Note:[/b] The order of the modifications can matter depending on the modifications. For example, modifications on a spine should operate before modifications on the arms in order to get proper results.
+			</description>
+		</method>
+		<method name="get_is_setup" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns a boolean that indiciates whether the modification stack is setup and can execute.
+			</description>
+		</method>
+		<method name="get_modification" qualifiers="const">
+			<return type="SkeletonModification3D" />
+			<argument index="0" name="mod_idx" type="int" />
+			<description>
+				Returns the [SkeletonModification3D] at the passed-in index, [code]mod_idx[/code].
+			</description>
+		</method>
+		<method name="get_skeleton" qualifiers="const">
+			<return type="Skeleton3D" />
+			<description>
+				Returns the [Skeleton3D] node that the SkeletonModificationStack3D is bound to.
+			</description>
+		</method>
+		<method name="set_modification">
+			<return type="void" />
+			<argument index="0" name="mod_idx" type="int" />
+			<argument index="1" name="modification" type="SkeletonModification3D" />
+			<description>
+				Sets the modification at [code]mod_idx[/code] to the passed-in modification, [code]modification[/code].
+			</description>
+		</method>
+		<method name="setup">
+			<return type="void" />
+			<description>
+				Sets up the modification stack so it can execute. This function should be called by [Skeleton3D] and shouldn't be called unless you know what you are doing.
+			</description>
+		</method>
+	</methods>
+	<members>
+		<member name="enabled" type="bool" setter="set_enabled" getter="get_enabled" default="false">
+			When true, the modification's in the stack will be called. This is handled automatically through the [Skeleton3D] node.
+		</member>
+		<member name="modification_count" type="int" setter="set_modification_count" getter="get_modification_count" default="0">
+			The amount of modifications in the stack.
+		</member>
+		<member name="strength" type="float" setter="set_strength" getter="get_strength" default="1.0">
+			The interpolation strength of the modifications in stack. A value of [code]0[/code] will make it where the modifications are not applied, a strength of [code]0.5[/code] will be half applied, and a strength of [code]1[/code] will allow the modifications to be fully applied and override the skeleton bone poses.
+		</member>
+	</members>
+	<constants>
+	</constants>
+</class>

editor/plugins/node_3d_editor_gizmos.cpp

@@ -2100,64 +2100,76 @@ void Skeleton3DGizmoPlugin::redraw(EditorNode3DGizmo *p_gizmo) {
 
 	surface_tool->begin(Mesh::PRIMITIVE_LINES);
 	surface_tool->set_material(material);
-	Vector<Transform3D> grests;
+	LocalVector<Transform3D> grests;
 	grests.resize(skel->get_bone_count());
 
-	Vector<int> bones;
-	Vector<float> weights;
+	LocalVector<int> bones;
+	LocalVector<real_t> weights;
 	bones.resize(4);
 	weights.resize(4);
 
 	for (int i = 0; i < 4; i++) {
-		bones.write[i] = 0;
-		weights.write[i] = 0;
+		bones[i] = 0;
+		weights[i] = 0;
 	}
 
-	weights.write[0] = 1;
+	weights[0] = 1;
 
 	AABB aabb;
 
 	Color bonecolor = Color(1.0, 0.4, 0.4, 0.3);
 	Color rootcolor = Color(0.4, 1.0, 0.4, 0.1);
 
-	for (int i_bone = 0; i_bone < skel->get_bone_count(); i_bone++) {
-		int i = skel->get_process_order(i_bone);
+	//LocalVector<int> bones_to_process = skel->get_parentless_bones();
+	LocalVector<int> bones_to_process;
+	bones_to_process = skel->get_parentless_bones();
 
-		int parent = skel->get_bone_parent(i);
+	while (bones_to_process.size() > 0) {
+		int current_bone_idx = bones_to_process[0];
+		bones_to_process.erase(current_bone_idx);
 
-		if (parent >= 0) {
-			grests.write[i] = grests[parent] * skel->get_bone_rest(i);
+		LocalVector<int> child_bones_vector;
+		child_bones_vector = skel->get_bone_children(current_bone_idx);
+		int child_bones_size = child_bones_vector.size();
 
-			Vector3 v0 = grests[parent].origin;
-			Vector3 v1 = grests[i].origin;
-			Vector3 d = (v1 - v0).normalized();
-			float dist = v0.distance_to(v1);
+		// You have children but no parent, then you must be a root/parentless bone.
+		if (child_bones_size >= 0 && skel->get_bone_parent(current_bone_idx) <= 0) {
+			grests[current_bone_idx] = skel->global_pose_to_local_pose(current_bone_idx, skel->get_bone_global_pose(current_bone_idx));
+		}
 
-			//find closest axis
-			int closest = -1;
-			float closest_d = 0.0;
+		for (int i = 0; i < child_bones_size; i++) {
+			int child_bone_idx = child_bones_vector[i];
 
+			grests[child_bone_idx] = skel->global_pose_to_local_pose(child_bone_idx, skel->get_bone_global_pose(child_bone_idx));
+			Vector3 v0 = grests[current_bone_idx].origin;
+			Vector3 v1 = grests[child_bone_idx].origin;
+			Vector3 d = skel->get_bone_rest(child_bone_idx).origin.normalized();
+			real_t dist = skel->get_bone_rest(child_bone_idx).origin.length();
+
+			// Find closest axis.
+			int closest = -1;
+			real_t closest_d = 0.0;
 			for (int j = 0; j < 3; j++) {
-				float dp = Math::abs(grests[parent].basis[j].normalized().dot(d));
+				real_t dp = Math::abs(grests[current_bone_idx].basis[j].normalized().dot(d));
 				if (j == 0 || dp > closest_d) {
 					closest = j;
 				}
 			}
 
-			//find closest other
+			// Find closest other.
 			Vector3 first;
 			Vector3 points[4];
-			int pointidx = 0;
+			int point_idx = 0;
 			for (int j = 0; j < 3; j++) {
-				bones.write[0] = parent;
+				bones[0] = current_bone_idx;
 				surface_tool->set_bones(bones);
 				surface_tool->set_weights(weights);
 				surface_tool->set_color(rootcolor);
-				surface_tool->add_vertex(v0 - grests[parent].basis[j].normalized() * dist * 0.05);
+				surface_tool->add_vertex(v0 - grests[current_bone_idx].basis[j].normalized() * dist * 0.05);
 				surface_tool->set_bones(bones);
 				surface_tool->set_weights(weights);
 				surface_tool->set_color(rootcolor);
-				surface_tool->add_vertex(v0 + grests[parent].basis[j].normalized() * dist * 0.05);
+				surface_tool->add_vertex(v0 + grests[current_bone_idx].basis[j].normalized() * dist * 0.05);
 
 				if (j == closest) {
 					continue;
@@ -2165,7 +2177,7 @@ void Skeleton3DGizmoPlugin::redraw(EditorNode3DGizmo *p_gizmo) {
 
 				Vector3 axis;
 				if (first == Vector3()) {
-					axis = d.cross(d.cross(grests[parent].basis[j])).normalized();
+					axis = d.cross(d.cross(grests[current_bone_idx].basis[j])).normalized();
 					first = axis;
 				} else {
 					axis = d.cross(first).normalized();
@@ -2178,7 +2190,7 @@ void Skeleton3DGizmoPlugin::redraw(EditorNode3DGizmo *p_gizmo) {
 					Vector3 point = v0 + d * dist * 0.2;
 					point += axis * dist * 0.1;
 
-					bones.write[0] = parent;
+					bones[0] = current_bone_idx;
 					surface_tool->set_bones(bones);
 					surface_tool->set_weights(weights);
 					surface_tool->set_color(bonecolor);
@@ -2188,23 +2200,22 @@ void Skeleton3DGizmoPlugin::redraw(EditorNode3DGizmo *p_gizmo) {
 					surface_tool->set_color(bonecolor);
 					surface_tool->add_vertex(point);
 
-					bones.write[0] = parent;
+					bones[0] = current_bone_idx;
 					surface_tool->set_bones(bones);
 					surface_tool->set_weights(weights);
 					surface_tool->set_color(bonecolor);
 					surface_tool->add_vertex(point);
-					bones.write[0] = i;
+					bones[0] = child_bone_idx;
 					surface_tool->set_bones(bones);
 					surface_tool->set_weights(weights);
 					surface_tool->set_color(bonecolor);
 					surface_tool->add_vertex(v1);
-					points[pointidx++] = point;
+					points[point_idx++] = point;
 				}
 			}
-
 			SWAP(points[1], points[2]);
 			for (int j = 0; j < 4; j++) {
-				bones.write[0] = parent;
+				bones[0] = current_bone_idx;
 				surface_tool->set_bones(bones);
 				surface_tool->set_weights(weights);
 				surface_tool->set_color(bonecolor);
@@ -2214,9 +2225,9 @@ void Skeleton3DGizmoPlugin::redraw(EditorNode3DGizmo *p_gizmo) {
 				surface_tool->set_color(bonecolor);
 				surface_tool->add_vertex(points[(j + 1) % 4]);
 			}
-		} else {
-			grests.write[i] = skel->get_bone_rest(i);
-			bones.write[0] = i;
+
+			// Add the bone's children to the list of bones to be processed.
+			bones_to_process.push_back(child_bones_vector[i]);
 		}
 	}
 

editor/plugins/node_3d_editor_gizmos.h

@@ -31,6 +31,7 @@
 #ifndef NODE_3D_EDITOR_GIZMOS_H
 #define NODE_3D_EDITOR_GIZMOS_H
 
+#include "core/templates/local_vector.h"
 #include "core/templates/ordered_hash_map.h"
 #include "scene/3d/node_3d.h"
 #include "scene/3d/skeleton_3d.h"

editor/plugins/skeleton_3d_editor_plugin.cpp

@@ -551,22 +551,30 @@ void Skeleton3DEditor::update_joint_tree() {
 
 	items.insert(-1, root);
 
-	const Vector<int> &joint_porder = skeleton->get_bone_process_orders();
 	Ref<Texture> bone_icon = get_theme_icon(SNAME("BoneAttachment3D"), SNAME("EditorIcons"));
 
-	for (int i = 0; i < joint_porder.size(); ++i) {
-		const int b_idx = joint_porder[i];
+	Vector<int> bones_to_process = skeleton->get_parentless_bones();
+	while (bones_to_process.size() > 0) {
+		int current_bone_idx = bones_to_process[0];
+		bones_to_process.erase(current_bone_idx);
 
-		const int p_idx = skeleton->get_bone_parent(b_idx);
-		TreeItem *p_item = items.find(p_idx)->get();
+		const int parent_idx = skeleton->get_bone_parent(current_bone_idx);
+		TreeItem *parent_item = items.find(parent_idx)->get();
 
-		TreeItem *joint_item = joint_tree->create_item(p_item);
-		items.insert(b_idx, joint_item);
+		TreeItem *joint_item = joint_tree->create_item(parent_item);
+		items.insert(current_bone_idx, joint_item);
 
-		joint_item->set_text(0, skeleton->get_bone_name(b_idx));
+		joint_item->set_text(0, skeleton->get_bone_name(current_bone_idx));
 		joint_item->set_icon(0, bone_icon);
 		joint_item->set_selectable(0, true);
-		joint_item->set_metadata(0, "bones/" + itos(b_idx));
+		joint_item->set_metadata(0, "bones/" + itos(current_bone_idx));
+
+		// Add the bone's children to the list of bones to be processed
+		Vector<int> current_bone_child_bones = skeleton->get_bone_children(current_bone_idx);
+		int child_bone_size = current_bone_child_bones.size();
+		for (int i = 0; i < child_bone_size; i++) {
+			bones_to_process.push_back(current_bone_child_bones[i]);
+		}
 	}
 }
 

scene/3d/bone_attachment_3d.cpp

@@ -32,7 +32,15 @@
 
 void BoneAttachment3D::_validate_property(PropertyInfo &property) const {
 	if (property.name == "bone_name") {
-		Skeleton3D *parent = Object::cast_to<Skeleton3D>(get_parent());
+		// Because it is a constant function, we cannot use the _get_skeleton_3d function.
+		const Skeleton3D *parent = nullptr;
+		if (use_external_skeleton) {
+			if (external_skeleton_node_cache.is_valid()) {
+				parent = Object::cast_to<Skeleton3D>(ObjectDB::get_instance(external_skeleton_node_cache));
+			}
+		} else {
+			parent = Object::cast_to<Skeleton3D>(get_parent());
+		}
 
 		if (parent) {
 			String names;
@@ -52,55 +60,321 @@ void BoneAttachment3D::_validate_property(PropertyInfo &property) const {
 	}
 }
 
+bool BoneAttachment3D::_set(const StringName &p_path, const Variant &p_value) {
+	if (p_path == SNAME("override_pose")) {
+		set_override_pose(p_value);
+	} else if (p_path == SNAME("override_mode")) {
+		set_override_mode(p_value);
+	} else if (p_path == SNAME("use_external_skeleton")) {
+		set_use_external_skeleton(p_value);
+	} else if (p_path == SNAME("external_skeleton")) {
+		set_external_skeleton(p_value);
+	}
+
+	return true;
+}
+
+bool BoneAttachment3D::_get(const StringName &p_path, Variant &r_ret) const {
+	if (p_path == SNAME("override_pose")) {
+		r_ret = get_override_pose();
+	} else if (p_path == SNAME("override_mode")) {
+		r_ret = get_override_mode();
+	} else if (p_path == SNAME("use_external_skeleton")) {
+		r_ret = get_use_external_skeleton();
+	} else if (p_path == SNAME("external_skeleton")) {
+		r_ret = get_external_skeleton();
+	}
+
+	return true;
+}
+
+void BoneAttachment3D::_get_property_list(List<PropertyInfo> *p_list) const {
+	p_list->push_back(PropertyInfo(Variant::BOOL, "override_pose", PROPERTY_HINT_NONE, ""));
+	if (override_pose) {
+		p_list->push_back(PropertyInfo(Variant::INT, "override_mode", PROPERTY_HINT_ENUM, "Global Pose Override, Local Pose Override, Custom Pose"));
+	}
+
+	p_list->push_back(PropertyInfo(Variant::BOOL, "use_external_skeleton", PROPERTY_HINT_NONE, ""));
+	if (use_external_skeleton) {
+		p_list->push_back(PropertyInfo(Variant::NODE_PATH, "external_skeleton", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "Skeleton3D"));
+	}
+}
+
+TypedArray<String> BoneAttachment3D::get_configuration_warnings() const {
+	TypedArray<String> warnings = Node3D::get_configuration_warnings();
+
+	if (use_external_skeleton) {
+		if (external_skeleton_node_cache.is_null()) {
+			warnings.append(TTR("External Skeleton3D node not set! Please set a path to an external Skeleton3D node."));
+		}
+	} else {
+		Skeleton3D *parent = Object::cast_to<Skeleton3D>(get_parent());
+		if (!parent) {
+			warnings.append(TTR("Parent node is not a Skeleton3D node! Please use an extenral Skeleton3D if you intend to use the BoneAttachment3D without it being a child of a Skeleton3D node."));
+		}
+	}
+
+	if (bone_idx == -1) {
+		warnings.append(TTR("BoneAttachment3D node is not bound to any bones! Please select a bone to attach this node."));
+	}
+
+	return warnings;
+}
+
+void BoneAttachment3D::_update_external_skeleton_cache() {
+	external_skeleton_node_cache = ObjectID();
+	if (has_node(external_skeleton_node)) {
+		Node *node = get_node(external_skeleton_node);
+		ERR_FAIL_COND_MSG(!node, "Cannot update external skeleton cache: Node cannot be found!");
+
+		// Make sure it's a skeleton3D
+		Skeleton3D *sk = Object::cast_to<Skeleton3D>(node);
+		ERR_FAIL_COND_MSG(!sk, "Cannot update external skeleton cache: Skeleton3D Nodepath does not point to a Skeleton3D node!");
+
+		external_skeleton_node_cache = node->get_instance_id();
+	} else {
+		if (external_skeleton_node.is_empty()) {
+			BoneAttachment3D *parent_attachment = Object::cast_to<BoneAttachment3D>(get_parent());
+			if (parent_attachment) {
+				parent_attachment->_update_external_skeleton_cache();
+				if (parent_attachment->has_node(parent_attachment->external_skeleton_node)) {
+					Node *node = parent_attachment->get_node(parent_attachment->external_skeleton_node);
+					ERR_FAIL_COND_MSG(!node, "Cannot update external skeleton cache: Parent's Skeleton3D node cannot be found!");
+
+					// Make sure it's a skeleton3D
+					Skeleton3D *sk = Object::cast_to<Skeleton3D>(node);
+					ERR_FAIL_COND_MSG(!sk, "Cannot update external skeleton cache: Parent Skeleton3D Nodepath does not point to a Skeleton3D node!");
+
+					external_skeleton_node_cache = node->get_instance_id();
+					external_skeleton_node = get_path_to(node);
+				}
+			}
+		}
+	}
+}
+
 void BoneAttachment3D::_check_bind() {
-	Skeleton3D *sk = Object::cast_to<Skeleton3D>(get_parent());
-	if (sk) {
-		int idx = sk->find_bone(bone_name);
-		if (idx != -1) {
-			sk->bind_child_node_to_bone(idx, this);
-			set_transform(sk->get_bone_global_pose(idx));
+	Skeleton3D *sk = _get_skeleton3d();
+
+	if (sk && !bound) {
+		if (bone_idx <= -1) {
+			bone_idx = sk->find_bone(bone_name);
+		}
+		if (bone_idx != -1) {
+			sk->call_deferred("connect", "bone_pose_changed", callable_mp(this, &BoneAttachment3D::on_bone_pose_update));
 			bound = true;
+			call_deferred(SNAME("on_bone_pose_update"), bone_idx);
+		}
+	}
+}
+
+Skeleton3D *BoneAttachment3D::_get_skeleton3d() {
+	if (use_external_skeleton) {
+		if (external_skeleton_node_cache.is_valid()) {
+			return Object::cast_to<Skeleton3D>(ObjectDB::get_instance(external_skeleton_node_cache));
+		} else {
+			_update_external_skeleton_cache();
+			if (external_skeleton_node_cache.is_valid()) {
+				return Object::cast_to<Skeleton3D>(ObjectDB::get_instance(external_skeleton_node_cache));
+			}
 		}
+	} else {
+		return Object::cast_to<Skeleton3D>(get_parent());
 	}
+	return nullptr;
 }
 
 void BoneAttachment3D::_check_unbind() {
 	if (bound) {
-		Skeleton3D *sk = Object::cast_to<Skeleton3D>(get_parent());
+		Skeleton3D *sk = _get_skeleton3d();
+
 		if (sk) {
-			int idx = sk->find_bone(bone_name);
-			if (idx != -1) {
-				sk->unbind_child_node_from_bone(idx, this);
-			}
+			sk->disconnect(SNAME("bone_pose_changed"), callable_mp(this, &BoneAttachment3D::on_bone_pose_update));
 		}
 		bound = false;
 	}
 }
 
+void BoneAttachment3D::_transform_changed() {
+	if (!is_inside_tree()) {
+		return;
+	}
+
+	if (override_pose) {
+		Skeleton3D *sk = _get_skeleton3d();
+
+		ERR_FAIL_COND_MSG(!sk, "Cannot override pose: Skeleton not found!");
+		ERR_FAIL_INDEX_MSG(bone_idx, sk->get_bone_count(), "Cannot override pose: Bone index is out of range!");
+
+		Transform3D our_trans = get_transform();
+		if (use_external_skeleton) {
+			our_trans = sk->world_transform_to_global_pose(get_global_transform());
+		}
+
+		if (override_mode == OVERRIDE_MODES::MODE_GLOBAL_POSE) {
+			sk->set_bone_global_pose_override(bone_idx, our_trans, 1.0, true);
+		} else if (override_mode == OVERRIDE_MODES::MODE_LOCAL_POSE) {
+			sk->set_bone_local_pose_override(bone_idx, sk->global_pose_to_local_pose(bone_idx, our_trans), 1.0, true);
+		} else if (override_mode == OVERRIDE_MODES::MODE_CUSTOM_POSE) {
+			sk->set_bone_custom_pose(bone_idx, sk->global_pose_to_local_pose(bone_idx, our_trans));
+		}
+	}
+}
+
 void BoneAttachment3D::set_bone_name(const String &p_name) {
+	bone_name = p_name;
+	Skeleton3D *sk = _get_skeleton3d();
+	if (sk) {
+		set_bone_idx(sk->find_bone(bone_name));
+	}
+}
+
+String BoneAttachment3D::get_bone_name() const {
+	return bone_name;
+}
+
+void BoneAttachment3D::set_bone_idx(const int &p_idx) {
 	if (is_inside_tree()) {
 		_check_unbind();
 	}
 
-	bone_name = p_name;
+	bone_idx = p_idx;
+
+	Skeleton3D *sk = _get_skeleton3d();
+	if (sk) {
+		if (bone_idx <= -1 || bone_idx >= sk->get_bone_count()) {
+			WARN_PRINT("Bone index out of range! Cannot connect BoneAttachment to node!");
+			bone_idx = -1;
+		} else {
+			bone_name = sk->get_bone_name(bone_idx);
+		}
+	}
 
 	if (is_inside_tree()) {
 		_check_bind();
 	}
+
+	notify_property_list_changed();
 }
 
-String BoneAttachment3D::get_bone_name() const {
-	return bone_name;
+int BoneAttachment3D::get_bone_idx() const {
+	return bone_idx;
+}
+
+void BoneAttachment3D::set_override_pose(bool p_override) {
+	override_pose = p_override;
+	set_notify_local_transform(override_pose);
+	set_process_internal(override_pose);
+
+	if (!override_pose) {
+		Skeleton3D *sk = _get_skeleton3d();
+		if (sk) {
+			if (override_mode == OVERRIDE_MODES::MODE_GLOBAL_POSE) {
+				sk->set_bone_global_pose_override(bone_idx, Transform3D(), 0.0, false);
+			} else if (override_mode == OVERRIDE_MODES::MODE_LOCAL_POSE) {
+				sk->set_bone_local_pose_override(bone_idx, Transform3D(), 0.0, false);
+			} else if (override_mode == OVERRIDE_MODES::MODE_CUSTOM_POSE) {
+				sk->set_bone_custom_pose(bone_idx, Transform3D());
+			}
+		}
+		_transform_changed();
+	}
+	notify_property_list_changed();
+}
+
+bool BoneAttachment3D::get_override_pose() const {
+	return override_pose;
+}
+
+void BoneAttachment3D::set_override_mode(int p_mode) {
+	if (override_pose) {
+		Skeleton3D *sk = _get_skeleton3d();
+		if (sk) {
+			if (override_mode == OVERRIDE_MODES::MODE_GLOBAL_POSE) {
+				sk->set_bone_global_pose_override(bone_idx, Transform3D(), 0.0, false);
+			} else if (override_mode == OVERRIDE_MODES::MODE_LOCAL_POSE) {
+				sk->set_bone_local_pose_override(bone_idx, Transform3D(), 0.0, false);
+			} else if (override_mode == OVERRIDE_MODES::MODE_CUSTOM_POSE) {
+				sk->set_bone_custom_pose(bone_idx, Transform3D());
+			}
+		}
+		override_mode = p_mode;
+		_transform_changed();
+		return;
+	}
+	override_mode = p_mode;
+}
+
+int BoneAttachment3D::get_override_mode() const {
+	return override_mode;
+}
+
+void BoneAttachment3D::set_use_external_skeleton(bool p_use_external) {
+	use_external_skeleton = p_use_external;
+
+	if (use_external_skeleton) {
+		_check_unbind();
+		_update_external_skeleton_cache();
+		_check_bind();
+		_transform_changed();
+	}
+
+	notify_property_list_changed();
+}
+
+bool BoneAttachment3D::get_use_external_skeleton() const {
+	return use_external_skeleton;
+}
+
+void BoneAttachment3D::set_external_skeleton(NodePath p_path) {
+	external_skeleton_node = p_path;
+	_update_external_skeleton_cache();
+	notify_property_list_changed();
+}
+
+NodePath BoneAttachment3D::get_external_skeleton() const {
+	return external_skeleton_node;
 }
 
 void BoneAttachment3D::_notification(int p_what) {
 	switch (p_what) {
 		case NOTIFICATION_ENTER_TREE: {
+			if (use_external_skeleton) {
+				_update_external_skeleton_cache();
+			}
 			_check_bind();
 		} break;
 		case NOTIFICATION_EXIT_TREE: {
 			_check_unbind();
 		} break;
+		case NOTIFICATION_LOCAL_TRANSFORM_CHANGED: {
+			_transform_changed();
+		} break;
+		case NOTIFICATION_INTERNAL_PROCESS: {
+			if (_override_dirty) {
+				_override_dirty = false;
+			}
+		}
+	}
+}
+
+void BoneAttachment3D::on_bone_pose_update(int p_bone_index) {
+	if (bone_idx == p_bone_index) {
+		Skeleton3D *sk = _get_skeleton3d();
+		if (sk) {
+			if (!override_pose) {
+				if (use_external_skeleton) {
+					set_global_transform(sk->global_pose_to_world_transform(sk->get_bone_global_pose(bone_idx)));
+				} else {
+					set_transform(sk->get_bone_global_pose(bone_idx));
+				}
+			} else {
+				if (!_override_dirty) {
+					_transform_changed();
+					_override_dirty = true;
+				}
+			}
+		}
 	}
 }
 
@@ -111,5 +385,21 @@ void BoneAttachment3D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("set_bone_name", "bone_name"), &BoneAttachment3D::set_bone_name);
 	ClassDB::bind_method(D_METHOD("get_bone_name"), &BoneAttachment3D::get_bone_name);
 
+	ClassDB::bind_method(D_METHOD("set_bone_idx", "bone_idx"), &BoneAttachment3D::set_bone_idx);
+	ClassDB::bind_method(D_METHOD("get_bone_idx"), &BoneAttachment3D::get_bone_idx);
+
+	ClassDB::bind_method(D_METHOD("on_bone_pose_update", "bone_index"), &BoneAttachment3D::on_bone_pose_update);
+
+	ClassDB::bind_method(D_METHOD("set_override_pose", "override_pose"), &BoneAttachment3D::set_override_pose);
+	ClassDB::bind_method(D_METHOD("get_override_pose"), &BoneAttachment3D::get_override_pose);
+	ClassDB::bind_method(D_METHOD("set_override_mode", "override_mode"), &BoneAttachment3D::set_override_mode);
+	ClassDB::bind_method(D_METHOD("get_override_mode"), &BoneAttachment3D::get_override_mode);
+
+	ClassDB::bind_method(D_METHOD("set_use_external_skeleton", "use_external_skeleton"), &BoneAttachment3D::set_use_external_skeleton);
+	ClassDB::bind_method(D_METHOD("get_use_external_skeleton"), &BoneAttachment3D::get_use_external_skeleton);
+	ClassDB::bind_method(D_METHOD("set_external_skeleton", "external_skeleton"), &BoneAttachment3D::set_external_skeleton);
+	ClassDB::bind_method(D_METHOD("get_external_skeleton"), &BoneAttachment3D::get_external_skeleton);
+
 	ADD_PROPERTY(PropertyInfo(Variant::STRING_NAME, "bone_name"), "set_bone_name", "get_bone_name");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "bone_idx"), "set_bone_idx", "get_bone_idx");
 }

scene/3d/bone_attachment_3d.h

@@ -38,20 +38,59 @@ class BoneAttachment3D : public Node3D {
 
 	bool bound = false;
 	String bone_name;
+	int bone_idx = -1;
+
+	bool override_pose = false;
+	int override_mode = 0;
+	bool _override_dirty = false;
+
+	enum OVERRIDE_MODES {
+		MODE_GLOBAL_POSE,
+		MODE_LOCAL_POSE,
+		MODE_CUSTOM_POSE
+	};
+
+	bool use_external_skeleton = false;
+	NodePath external_skeleton_node;
+	ObjectID external_skeleton_node_cache;
 
 	void _check_bind();
 	void _check_unbind();
 
+	void _transform_changed();
+	void _update_external_skeleton_cache();
+	Skeleton3D *_get_skeleton3d();
+
 protected:
 	virtual void _validate_property(PropertyInfo &property) const override;
+	bool _get(const StringName &p_path, Variant &r_ret) const;
+	bool _set(const StringName &p_path, const Variant &p_value);
+	void _get_property_list(List<PropertyInfo> *p_list) const;
 	void _notification(int p_what);
 
 	static void _bind_methods();
 
 public:
+	virtual TypedArray<String> get_configuration_warnings() const override;
+
 	void set_bone_name(const String &p_name);
 	String get_bone_name() const;
 
+	void set_bone_idx(const int &p_idx);
+	int get_bone_idx() const;
+
+	void set_override_pose(bool p_override);
+	bool get_override_pose() const;
+	void set_override_mode(int p_mode);
+	int get_override_mode() const;
+
+	void set_use_external_skeleton(bool p_external_skeleton);
+	bool get_use_external_skeleton() const;
+	void set_external_skeleton(NodePath p_skeleton);
+	NodePath get_external_skeleton() const;
+
+	virtual void on_bone_pose_update(int p_bone_index);
+
 	BoneAttachment3D();
 };
 

scene/3d/physics_body_3d.cpp

@@ -2199,7 +2199,6 @@ void PhysicalBone3D::_notification(int p_what) {
 			if (parent_skeleton) {
 				if (-1 != bone_id) {
 					parent_skeleton->unbind_physical_bone_from_bone(bone_id);
-					parent_skeleton->unbind_child_node_from_bone(bone_id, this);
 					bone_id = -1;
 				}
 			}
@@ -2656,7 +2655,6 @@ void PhysicalBone3D::update_bone_id() {
 		if (-1 != bone_id) {
 			// Assert the unbind from old node
 			parent_skeleton->unbind_physical_bone_from_bone(bone_id);
-			parent_skeleton->unbind_child_node_from_bone(bone_id, this);
 		}
 
 		bone_id = new_bone_id;

scene/3d/skeleton_3d.cpp

@@ -31,7 +31,10 @@
 #include "skeleton_3d.h"
 
 #include "core/object/message_queue.h"
+#include "core/variant/type_info.h"
 #include "scene/3d/physics_body_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+#include "scene/resources/surface_tool.h"
 #include "scene/scene_string_names.h"
 
 void SkinReference::_skin_changed() {
@@ -68,6 +71,13 @@ SkinReference::~SkinReference() {
 bool Skeleton3D::_set(const StringName &p_path, const Variant &p_value) {
 	String path = p_path;
 
+#ifndef _3D_DISABLED
+	if (path.begins_with("modification_stack")) {
+		set_modification_stack(p_value);
+		return true;
+	}
+#endif //_3D_DISABLED
+
 	if (!path.begins_with("bones/")) {
 		return false;
 	}
@@ -100,6 +110,13 @@ bool Skeleton3D::_set(const StringName &p_path, const Variant &p_value) {
 bool Skeleton3D::_get(const StringName &p_path, Variant &r_ret) const {
 	String path = p_path;
 
+#ifndef _3D_DISABLED
+	if (path.begins_with("modification_stack")) {
+		r_ret = modification_stack;
+		return true;
+	}
+#endif //_3D_DISABLED
+
 	if (!path.begins_with("bones/")) {
 		return false;
 	}
@@ -135,6 +152,14 @@ void Skeleton3D::_get_property_list(List<PropertyInfo> *p_list) const {
 		p_list->push_back(PropertyInfo(Variant::BOOL, prep + "enabled", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NOEDITOR));
 		p_list->push_back(PropertyInfo(Variant::TRANSFORM3D, prep + "pose", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_NOEDITOR));
 	}
+
+#ifndef _3D_DISABLED
+	p_list->push_back(
+			PropertyInfo(Variant::OBJECT, "modification_stack",
+					PROPERTY_HINT_RESOURCE_TYPE,
+					"SkeletonModificationStack3D",
+					PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_DEFERRED_SET_RESOURCE | PROPERTY_USAGE_DO_NOT_SHARE_ON_DUPLICATE));
+#endif //_3D_DISABLED
 }
 
 void Skeleton3D::_update_process_order() {
@@ -145,47 +170,29 @@ void Skeleton3D::_update_process_order() {
 	Bone *bonesptr = bones.ptrw();
 	int len = bones.size();
 
-	process_order.resize(len);
-	int *order = process_order.ptrw();
+	parentless_bones.clear();
+
 	for (int i = 0; i < len; i++) {
 		if (bonesptr[i].parent >= len) {
 			//validate this just in case
 			ERR_PRINT("Bone " + itos(i) + " has invalid parent: " + itos(bonesptr[i].parent));
 			bonesptr[i].parent = -1;
 		}
-		order[i] = i;
-		bonesptr[i].sort_index = i;
-	}
-	//now check process order
-	int pass_count = 0;
-	while (pass_count < len * len) {
-		//using bubblesort because of simplicity, it won't run every frame though.
-		//bublesort worst case is O(n^2), and this may be an infinite loop if cyclic
-		bool swapped = false;
-		for (int i = 0; i < len; i++) {
-			int parent_idx = bonesptr[order[i]].parent;
-			if (parent_idx < 0) {
-				continue; //do nothing because it has no parent
-			}
-			//swap indices
-			int parent_order = bonesptr[parent_idx].sort_index;
-			if (parent_order > i) {
-				bonesptr[order[i]].sort_index = parent_order;
-				bonesptr[parent_idx].sort_index = i;
-				//swap order
-				SWAP(order[i], order[parent_order]);
-				swapped = true;
-			}
-		}
+		bonesptr[i].child_bones.clear();
 
-		if (!swapped) {
-			break;
-		}
-		pass_count++;
-	}
+		if (bonesptr[i].parent != -1) {
+			int parent_bone_idx = bonesptr[i].parent;
 
-	if (pass_count == len * len) {
-		ERR_PRINT("Skeleton3D parenthood graph is cyclic");
+			// Check to see if this node is already added to the parent:
+			if (bonesptr[parent_bone_idx].child_bones.find(i) < 0) {
+				// Add the child node
+				bonesptr[parent_bone_idx].child_bones.push_back(i);
+			} else {
+				ERR_PRINT("Skeleton3D parenthood graph is cyclic");
+			}
+		} else {
+			parentless_bones.push_back(i);
+		}
 	}
 
 	process_order_dirty = false;
@@ -196,78 +203,12 @@ void Skeleton3D::_notification(int p_what) {
 		case NOTIFICATION_UPDATE_SKELETON: {
 			RenderingServer *rs = RenderingServer::get_singleton();
 			Bone *bonesptr = bones.ptrw();
-			int len = bones.size();
-
-			_update_process_order();
-
-			const int *order = process_order.ptr();
-
-			for (int i = 0; i < len; i++) {
-				Bone &b = bonesptr[order[i]];
-
-				if (b.disable_rest) {
-					if (b.enabled) {
-						Transform3D pose = b.pose;
-						if (b.custom_pose_enable) {
-							pose = b.custom_pose * pose;
-						}
-						if (b.parent >= 0) {
-							b.pose_global = bonesptr[b.parent].pose_global * pose;
-							b.pose_global_no_override = bonesptr[b.parent].pose_global * pose;
-						} else {
-							b.pose_global = pose;
-							b.pose_global_no_override = pose;
-						}
-					} else {
-						if (b.parent >= 0) {
-							b.pose_global = bonesptr[b.parent].pose_global;
-							b.pose_global_no_override = bonesptr[b.parent].pose_global;
-						} else {
-							b.pose_global = Transform3D();
-							b.pose_global_no_override = Transform3D();
-						}
-					}
-
-				} else {
-					if (b.enabled) {
-						Transform3D pose = b.pose;
-						if (b.custom_pose_enable) {
-							pose = b.custom_pose * pose;
-						}
-						if (b.parent >= 0) {
-							b.pose_global = bonesptr[b.parent].pose_global * (b.rest * pose);
-							b.pose_global_no_override = bonesptr[b.parent].pose_global * (b.rest * pose);
-						} else {
-							b.pose_global = b.rest * pose;
-							b.pose_global_no_override = b.rest * pose;
-						}
-					} else {
-						if (b.parent >= 0) {
-							b.pose_global = bonesptr[b.parent].pose_global * b.rest;
-							b.pose_global_no_override = bonesptr[b.parent].pose_global * b.rest;
-						} else {
-							b.pose_global = b.rest;
-							b.pose_global_no_override = b.rest;
-						}
-					}
-				}
 
-				if (b.global_pose_override_amount >= CMP_EPSILON) {
-					b.pose_global = b.pose_global.interpolate_with(b.global_pose_override, b.global_pose_override_amount);
-				}
-
-				if (b.global_pose_override_reset) {
-					b.global_pose_override_amount = 0.0;
-				}
+			int len = bones.size();
+			dirty = false;
 
-				for (const ObjectID &E : b.nodes_bound) {
-					Object *obj = ObjectDB::get_instance(E);
-					ERR_CONTINUE(!obj);
-					Node3D *node_3d = Object::cast_to<Node3D>(obj);
-					ERR_CONTINUE(!node_3d);
-					node_3d->set_transform(b.pose_global);
-				}
-			}
+			// Update bone transforms
+			force_update_all_bone_transforms();
 
 			//update skins
 			for (Set<SkinReference *>::Element *E = skin_bindings.front(); E; E = E->next()) {
@@ -325,32 +266,53 @@ void Skeleton3D::_notification(int p_what) {
 				}
 			}
 
-			dirty = false;
-
 #ifdef TOOLS_ENABLED
 			emit_signal(SceneStringNames::get_singleton()->pose_updated);
 #endif // TOOLS_ENABLED
 
 		} break;
 
+#ifndef _3D_DISABLED
 		case NOTIFICATION_INTERNAL_PHYSICS_PROCESS: {
 			// This is active only if the skeleton animates the physical bones
 			// and the state of the bone is not active.
-			if (animate_physical_bones) {
-				for (int i = 0; i < bones.size(); i += 1) {
-					if (bones[i].physical_bone) {
-						if (bones[i].physical_bone->is_simulating_physics() == false) {
-							bones[i].physical_bone->reset_to_rest_position();
+			if (Engine::get_singleton()->is_editor_hint()) {
+				if (animate_physical_bones) {
+					for (int i = 0; i < bones.size(); i += 1) {
+						if (bones[i].physical_bone) {
+							if (bones[i].physical_bone->is_simulating_physics() == false) {
+								bones[i].physical_bone->reset_to_rest_position();
+							}
 						}
 					}
 				}
 			}
+
+			if (modification_stack.is_valid()) {
+				execute_modifications(get_physics_process_delta_time(), SkeletonModificationStack3D::EXECUTION_MODE::execution_mode_physics_process);
+			}
+
 		} break;
+#endif // _3D_DISABLED
+
+#ifndef _3D_DISABLED
+		case NOTIFICATION_INTERNAL_PROCESS: {
+			if (modification_stack.is_valid()) {
+				execute_modifications(get_process_delta_time(), SkeletonModificationStack3D::EXECUTION_MODE::execution_mode_process);
+			}
+		} break;
+#endif // _3D_DISABLED
+
+#ifndef _3D_DISABLED
 		case NOTIFICATION_READY: {
-			if (Engine::get_singleton()->is_editor_hint()) {
-				set_physics_process_internal(true);
+			set_physics_process_internal(true);
+			set_process_internal(true);
+
+			if (modification_stack.is_valid()) {
+				set_modification_stack(modification_stack);
 			}
 		} break;
+#endif // _3D_DISABLED
 	}
 }
 
@@ -363,15 +325,23 @@ void Skeleton3D::clear_bones_global_pose_override() {
 }
 
 void Skeleton3D::set_bone_global_pose_override(int p_bone, const Transform3D &p_pose, real_t p_amount, bool p_persistent) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 	bones.write[p_bone].global_pose_override_amount = p_amount;
 	bones.write[p_bone].global_pose_override = p_pose;
 	bones.write[p_bone].global_pose_override_reset = !p_persistent;
 	_make_dirty();
 }
 
+Transform3D Skeleton3D::get_bone_global_pose_override(int p_bone) const {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, Transform3D());
+	return bones[p_bone].global_pose_override;
+}
+
 Transform3D Skeleton3D::get_bone_global_pose(int p_bone) const {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), Transform3D());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, Transform3D());
 	if (dirty) {
 		const_cast<Skeleton3D *>(this)->notification(NOTIFICATION_UPDATE_SKELETON);
 	}
@@ -379,13 +349,107 @@ Transform3D Skeleton3D::get_bone_global_pose(int p_bone) const {
 }
 
 Transform3D Skeleton3D::get_bone_global_pose_no_override(int p_bone) const {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), Transform3D());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, Transform3D());
 	if (dirty) {
 		const_cast<Skeleton3D *>(this)->notification(NOTIFICATION_UPDATE_SKELETON);
 	}
 	return bones[p_bone].pose_global_no_override;
 }
 
+void Skeleton3D::clear_bones_local_pose_override() {
+	for (int i = 0; i < bones.size(); i += 1) {
+		bones.write[i].local_pose_override_amount = 0;
+	}
+	_make_dirty();
+}
+
+void Skeleton3D::set_bone_local_pose_override(int p_bone, const Transform3D &p_pose, real_t p_amount, bool p_persistent) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
+	bones.write[p_bone].local_pose_override_amount = p_amount;
+	bones.write[p_bone].local_pose_override = p_pose;
+	bones.write[p_bone].local_pose_override_reset = !p_persistent;
+	_make_dirty();
+}
+
+Transform3D Skeleton3D::get_bone_local_pose_override(int p_bone) const {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, Transform3D());
+	return bones[p_bone].local_pose_override;
+}
+
+void Skeleton3D::update_bone_rest_forward_vector(int p_bone, bool p_force_update) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
+
+	if (bones[p_bone].rest_bone_forward_vector.length_squared() > 0 && p_force_update == false) {
+		update_bone_rest_forward_axis(p_bone, p_force_update);
+	}
+
+	// If it is a child/leaf bone...
+	if (get_bone_parent(p_bone) > 0) {
+		bones.write[p_bone].rest_bone_forward_vector = bones[p_bone].rest.origin.normalized();
+	} else {
+		// If it has children...
+		Vector<int> child_bones = get_bone_children(p_bone);
+		if (child_bones.size() > 0) {
+			Vector3 combined_child_dir = Vector3(0, 0, 0);
+			for (int i = 0; i < child_bones.size(); i++) {
+				combined_child_dir += bones[child_bones[i]].rest.origin.normalized();
+			}
+			combined_child_dir = combined_child_dir / child_bones.size();
+			bones.write[p_bone].rest_bone_forward_vector = combined_child_dir.normalized();
+		} else {
+			WARN_PRINT_ONCE("Cannot calculate forward direction for bone " + itos(p_bone));
+			WARN_PRINT_ONCE("Assuming direction of (0, 1, 0) for bone");
+			bones.write[p_bone].rest_bone_forward_vector = Vector3(0, 1, 0);
+		}
+	}
+	update_bone_rest_forward_axis(p_bone, p_force_update);
+}
+
+void Skeleton3D::update_bone_rest_forward_axis(int p_bone, bool p_force_update) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
+	if (bones[p_bone].rest_bone_forward_axis > -1 && p_force_update == false) {
+		return;
+	}
+
+	Vector3 forward_axis_absolute = bones[p_bone].rest_bone_forward_vector.abs();
+	if (forward_axis_absolute.x > forward_axis_absolute.y && forward_axis_absolute.x > forward_axis_absolute.z) {
+		if (bones[p_bone].rest_bone_forward_vector.x > 0) {
+			bones.write[p_bone].rest_bone_forward_axis = BONE_AXIS_X_FORWARD;
+		} else {
+			bones.write[p_bone].rest_bone_forward_axis = BONE_AXIS_NEGATIVE_X_FORWARD;
+		}
+	} else if (forward_axis_absolute.y > forward_axis_absolute.x && forward_axis_absolute.y > forward_axis_absolute.z) {
+		if (bones[p_bone].rest_bone_forward_vector.y > 0) {
+			bones.write[p_bone].rest_bone_forward_axis = BONE_AXIS_Y_FORWARD;
+		} else {
+			bones.write[p_bone].rest_bone_forward_axis = BONE_AXIS_NEGATIVE_Y_FORWARD;
+		}
+	} else {
+		if (bones[p_bone].rest_bone_forward_vector.z > 0) {
+			bones.write[p_bone].rest_bone_forward_axis = BONE_AXIS_Z_FORWARD;
+		} else {
+			bones.write[p_bone].rest_bone_forward_axis = BONE_AXIS_NEGATIVE_Z_FORWARD;
+		}
+	}
+}
+
+Vector3 Skeleton3D::get_bone_axis_forward_vector(int p_bone) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, Vector3(0, 0, 0));
+	return bones[p_bone].rest_bone_forward_vector;
+}
+
+int Skeleton3D::get_bone_axis_forward_enum(int p_bone) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, -1);
+	return bones[p_bone].rest_bone_forward_axis;
+}
+
 // skeleton creation api
 void Skeleton3D::add_bone(const String &p_name) {
 	ERR_FAIL_COND(p_name == "" || p_name.find(":") != -1 || p_name.find("/") != -1);
@@ -414,14 +478,15 @@ int Skeleton3D::find_bone(const String &p_name) const {
 }
 
 String Skeleton3D::get_bone_name(int p_bone) const {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), "");
-
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, "");
 	return bones[p_bone].name;
 }
 void Skeleton3D::set_bone_name(int p_bone, const String &p_name) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 
-	for (int i = 0; i < bones.size(); i++) {
+	for (int i = 0; i < bone_size; i++) {
 		if (i != p_bone) {
 			ERR_FAIL_COND(bones[i].name == p_name);
 		}
@@ -449,7 +514,8 @@ int Skeleton3D::get_bone_count() const {
 }
 
 void Skeleton3D::set_bone_parent(int p_bone, int p_parent) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 	ERR_FAIL_COND(p_parent != -1 && (p_parent < 0));
 
 	bones.write[p_bone].parent = p_parent;
@@ -458,7 +524,8 @@ void Skeleton3D::set_bone_parent(int p_bone, int p_parent) {
 }
 
 void Skeleton3D::unparent_bone_and_rest(int p_bone) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 
 	_update_process_order();
 
@@ -475,76 +542,93 @@ void Skeleton3D::unparent_bone_and_rest(int p_bone) {
 }
 
 void Skeleton3D::set_bone_disable_rest(int p_bone, bool p_disable) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 	bones.write[p_bone].disable_rest = p_disable;
 }
 
 bool Skeleton3D::is_bone_rest_disabled(int p_bone) const {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), false);
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, false);
 	return bones[p_bone].disable_rest;
 }
 
 int Skeleton3D::get_bone_parent(int p_bone) const {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), -1);
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, -1);
 
 	return bones[p_bone].parent;
 }
 
-void Skeleton3D::set_bone_rest(int p_bone, const Transform3D &p_rest) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+Vector<int> Skeleton3D::get_bone_children(int p_bone) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, Vector<int>());
+	return bones[p_bone].child_bones;
+}
 
-	bones.write[p_bone].rest = p_rest;
+void Skeleton3D::set_bone_children(int p_bone, Vector<int> p_children) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
+	bones.write[p_bone].child_bones = p_children;
+
+	process_order_dirty = true;
 	_make_dirty();
 }
-Transform3D Skeleton3D::get_bone_rest(int p_bone) const {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), Transform3D());
 
-	return bones[p_bone].rest;
+void Skeleton3D::add_bone_child(int p_bone, int p_child) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
+	bones.write[p_bone].child_bones.push_back(p_child);
+
+	process_order_dirty = true;
+	_make_dirty();
 }
 
-void Skeleton3D::set_bone_enabled(int p_bone, bool p_enabled) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+void Skeleton3D::remove_bone_child(int p_bone, int p_child) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 
-	bones.write[p_bone].enabled = p_enabled;
+	int child_idx = bones[p_bone].child_bones.find(p_child);
+	if (child_idx >= 0) {
+		bones.write[p_bone].child_bones.remove(child_idx);
+	} else {
+		WARN_PRINT("Cannot remove child bone: Child bone not found.");
+	}
+
+	process_order_dirty = true;
 	_make_dirty();
 }
 
-bool Skeleton3D::is_bone_enabled(int p_bone) const {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), false);
-	return bones[p_bone].enabled;
+Vector<int> Skeleton3D::get_parentless_bones() {
+	return parentless_bones;
 }
 
-void Skeleton3D::bind_child_node_to_bone(int p_bone, Node *p_node) {
-	ERR_FAIL_NULL(p_node);
-	ERR_FAIL_INDEX(p_bone, bones.size());
-
-	ObjectID id = p_node->get_instance_id();
+void Skeleton3D::set_bone_rest(int p_bone, const Transform3D &p_rest) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 
-	for (const ObjectID &E : bones[p_bone].nodes_bound) {
-		if (E == id) {
-			return; // already here
-		}
-	}
+	bones.write[p_bone].rest = p_rest;
+	_make_dirty();
+}
+Transform3D Skeleton3D::get_bone_rest(int p_bone) const {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, Transform3D());
 
-	bones.write[p_bone].nodes_bound.push_back(id);
+	return bones[p_bone].rest;
 }
 
-void Skeleton3D::unbind_child_node_from_bone(int p_bone, Node *p_node) {
-	ERR_FAIL_NULL(p_node);
-	ERR_FAIL_INDEX(p_bone, bones.size());
+void Skeleton3D::set_bone_enabled(int p_bone, bool p_enabled) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 
-	ObjectID id = p_node->get_instance_id();
-	bones.write[p_bone].nodes_bound.erase(id);
+	bones.write[p_bone].enabled = p_enabled;
+	_make_dirty();
 }
 
-void Skeleton3D::get_bound_child_nodes_to_bone(int p_bone, List<Node *> *p_bound) const {
-	ERR_FAIL_INDEX(p_bone, bones.size());
-
-	for (const ObjectID &E : bones[p_bone].nodes_bound) {
-		Object *obj = ObjectDB::get_instance(E);
-		ERR_CONTINUE(!obj);
-		p_bound->push_back(Object::cast_to<Node>(obj));
-	}
+bool Skeleton3D::is_bone_enabled(int p_bone) const {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, false);
+	return bones[p_bone].enabled;
 }
 
 void Skeleton3D::clear_bones() {
@@ -557,7 +641,8 @@ void Skeleton3D::clear_bones() {
 // posing api
 
 void Skeleton3D::set_bone_pose(int p_bone, const Transform3D &p_pose) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 
 	bones.write[p_bone].pose = p_pose;
 	if (is_inside_tree()) {
@@ -565,12 +650,14 @@ void Skeleton3D::set_bone_pose(int p_bone, const Transform3D &p_pose) {
 	}
 }
 Transform3D Skeleton3D::get_bone_pose(int p_bone) const {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), Transform3D());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, Transform3D());
 	return bones[p_bone].pose;
 }
 
 void Skeleton3D::set_bone_custom_pose(int p_bone, const Transform3D &p_custom_pose) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 	//ERR_FAIL_COND( !is_inside_scene() );
 
 	bones.write[p_bone].custom_pose_enable = (p_custom_pose != Transform3D());
@@ -580,7 +667,8 @@ void Skeleton3D::set_bone_custom_pose(int p_bone, const Transform3D &p_custom_po
 }
 
 Transform3D Skeleton3D::get_bone_custom_pose(int p_bone) const {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), Transform3D());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, Transform3D());
 	return bones[p_bone].custom_pose;
 }
 
@@ -593,24 +681,22 @@ void Skeleton3D::_make_dirty() {
 	dirty = true;
 }
 
-int Skeleton3D::get_process_order(int p_idx) {
-	ERR_FAIL_INDEX_V(p_idx, bones.size(), -1);
+void Skeleton3D::localize_rests() {
 	_update_process_order();
-	return process_order[p_idx];
-}
 
-Vector<int> Skeleton3D::get_bone_process_orders() {
-	_update_process_order();
-	return process_order;
-}
+	Vector<int> bones_to_process = get_parentless_bones();
+	while (bones_to_process.size() > 0) {
+		int current_bone_idx = bones_to_process[0];
+		bones_to_process.erase(current_bone_idx);
 
-void Skeleton3D::localize_rests() {
-	_update_process_order();
+		if (bones[current_bone_idx].parent >= 0) {
+			set_bone_rest(current_bone_idx, bones[bones[current_bone_idx].parent].rest.affine_inverse() * bones[current_bone_idx].rest);
+		}
 
-	for (int i = bones.size() - 1; i >= 0; i--) {
-		int idx = process_order[i];
-		if (bones[idx].parent >= 0) {
-			set_bone_rest(idx, bones[bones[idx].parent].rest.affine_inverse() * bones[idx].rest);
+		// Add the bone's children to the list of bones to be processed
+		int child_bone_size = bones[current_bone_idx].child_bones.size();
+		for (int i = 0; i < child_bone_size; i++) {
+			bones_to_process.push_back(bones[current_bone_idx].child_bones[i]);
 		}
 	}
 }
@@ -637,7 +723,8 @@ bool Skeleton3D::get_animate_physical_bones() const {
 }
 
 void Skeleton3D::bind_physical_bone_to_bone(int p_bone, PhysicalBone3D *p_physical_bone) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 	ERR_FAIL_COND(bones[p_bone].physical_bone);
 	ERR_FAIL_COND(!p_physical_bone);
 	bones.write[p_bone].physical_bone = p_physical_bone;
@@ -646,20 +733,23 @@ void Skeleton3D::bind_physical_bone_to_bone(int p_bone, PhysicalBone3D *p_physic
 }
 
 void Skeleton3D::unbind_physical_bone_from_bone(int p_bone) {
-	ERR_FAIL_INDEX(p_bone, bones.size());
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone, bone_size);
 	bones.write[p_bone].physical_bone = nullptr;
 
 	_rebuild_physical_bones_cache();
 }
 
 PhysicalBone3D *Skeleton3D::get_physical_bone(int p_bone) {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), nullptr);
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, nullptr);
 
 	return bones[p_bone].physical_bone;
 }
 
 PhysicalBone3D *Skeleton3D::get_physical_bone_parent(int p_bone) {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), nullptr);
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, nullptr);
 
 	if (bones[p_bone].cache_parent_physical_bone) {
 		return bones[p_bone].cache_parent_physical_bone;
@@ -669,7 +759,8 @@ PhysicalBone3D *Skeleton3D::get_physical_bone_parent(int p_bone) {
 }
 
 PhysicalBone3D *Skeleton3D::_get_physical_bone_parent(int p_bone) {
-	ERR_FAIL_INDEX_V(p_bone, bones.size(), nullptr);
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone, bone_size, nullptr);
 
 	const int parent_bone = bones[p_bone].parent;
 	if (0 > parent_bone) {
@@ -800,15 +891,20 @@ Ref<SkinReference> Skeleton3D::register_skin(const Ref<Skin> &p_skin) {
 		// pose changed, rebuild cache of inverses
 		const Bone *bonesptr = bones.ptr();
 		int len = bones.size();
-		const int *order = process_order.ptr();
 
 		// calculate global rests and invert them
-		for (int i = 0; i < len; i++) {
-			const Bone &b = bonesptr[order[i]];
+		Vector<int> bones_to_process = get_parentless_bones();
+		while (bones_to_process.size() > 0) {
+			int current_bone_idx = bones_to_process[0];
+			bones_to_process.erase(current_bone_idx);
+			const Bone &b = bonesptr[current_bone_idx];
+
+			// Note: the code below may not work by default. May need to track an integer for the bone pose index order
+			// in the while loop, instead of using current_bone_idx.
 			if (b.parent >= 0) {
-				skin->set_bind_pose(order[i], skin->get_bind_pose(b.parent) * b.rest);
+				skin->set_bind_pose(current_bone_idx, skin->get_bind_pose(b.parent) * b.rest);
 			} else {
-				skin->set_bind_pose(order[i], b.rest);
+				skin->set_bind_pose(current_bone_idx, b.rest);
 			}
 		}
 
@@ -839,17 +935,202 @@ Ref<SkinReference> Skeleton3D::register_skin(const Ref<Skin> &p_skin) {
 	return skin_ref;
 }
 
+void Skeleton3D::force_update_all_bone_transforms() {
+	_update_process_order();
+
+	for (int i = 0; i < parentless_bones.size(); i++) {
+		force_update_bone_children_transforms(parentless_bones[i]);
+	}
+}
+
+void Skeleton3D::force_update_bone_children_transforms(int p_bone_idx) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX(p_bone_idx, bone_size);
+
+	Bone *bonesptr = bones.ptrw();
+	List<int> bones_to_process = List<int>();
+	bones_to_process.push_back(p_bone_idx);
+
+	while (bones_to_process.size() > 0) {
+		int current_bone_idx = bones_to_process[0];
+		bones_to_process.erase(current_bone_idx);
+
+		Bone &b = bonesptr[current_bone_idx];
+
+		if (b.disable_rest) {
+			if (b.enabled) {
+				Transform3D pose = b.pose;
+				if (b.custom_pose_enable) {
+					pose = b.custom_pose * pose;
+				}
+				if (b.parent >= 0) {
+					b.pose_global = bonesptr[b.parent].pose_global * pose;
+					b.pose_global_no_override = b.pose_global;
+				} else {
+					b.pose_global = pose;
+					b.pose_global_no_override = b.pose_global;
+				}
+			} else {
+				if (b.parent >= 0) {
+					b.pose_global = bonesptr[b.parent].pose_global;
+					b.pose_global_no_override = b.pose_global;
+				} else {
+					b.pose_global = Transform3D();
+					b.pose_global_no_override = b.pose_global;
+				}
+			}
+
+		} else {
+			if (b.enabled) {
+				Transform3D pose = b.pose;
+				if (b.custom_pose_enable) {
+					pose = b.custom_pose * pose;
+				}
+				if (b.parent >= 0) {
+					b.pose_global = bonesptr[b.parent].pose_global * (b.rest * pose);
+					b.pose_global_no_override = b.pose_global;
+				} else {
+					b.pose_global = b.rest * pose;
+					b.pose_global_no_override = b.pose_global;
+				}
+			} else {
+				if (b.parent >= 0) {
+					b.pose_global = bonesptr[b.parent].pose_global * b.rest;
+					b.pose_global_no_override = b.pose_global;
+				} else {
+					b.pose_global = b.rest;
+					b.pose_global_no_override = b.pose_global;
+				}
+			}
+		}
+
+		if (b.local_pose_override_amount >= CMP_EPSILON) {
+			Transform3D override_local_pose;
+			if (b.parent >= 0) {
+				override_local_pose = bonesptr[b.parent].pose_global * (b.rest * b.local_pose_override);
+			} else {
+				override_local_pose = (b.rest * b.local_pose_override);
+			}
+			b.pose_global = b.pose_global.interpolate_with(override_local_pose, b.local_pose_override_amount);
+		}
+
+		if (b.global_pose_override_amount >= CMP_EPSILON) {
+			b.pose_global = b.pose_global.interpolate_with(b.global_pose_override, b.global_pose_override_amount);
+		}
+
+		if (b.local_pose_override_reset) {
+			b.local_pose_override_amount = 0.0;
+		}
+		if (b.global_pose_override_reset) {
+			b.global_pose_override_amount = 0.0;
+		}
+
+		// Add the bone's children to the list of bones to be processed
+		int child_bone_size = b.child_bones.size();
+		for (int i = 0; i < child_bone_size; i++) {
+			bones_to_process.push_back(b.child_bones[i]);
+		}
+
+		emit_signal(SceneStringNames::get_singleton()->bone_pose_changed, current_bone_idx);
+	}
+}
+
 // helper functions
-Transform3D Skeleton3D::bone_transform_to_world_transform(Transform3D p_bone_transform) {
-	return get_global_transform() * p_bone_transform;
+
+Transform3D Skeleton3D::global_pose_to_world_transform(Transform3D p_global_pose) {
+	return get_global_transform() * p_global_pose;
 }
 
-Transform3D Skeleton3D::world_transform_to_bone_transform(Transform3D p_world_transform) {
+Transform3D Skeleton3D::world_transform_to_global_pose(Transform3D p_world_transform) {
 	return get_global_transform().affine_inverse() * p_world_transform;
 }
 
+Transform3D Skeleton3D::global_pose_to_local_pose(int p_bone_idx, Transform3D p_global_pose) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone_idx, bone_size, Transform3D());
+	if (bones[p_bone_idx].parent >= 0) {
+		int parent_bone_idx = bones[p_bone_idx].parent;
+		Transform3D conversion_transform = (bones[parent_bone_idx].pose_global * bones[p_bone_idx].rest);
+		return conversion_transform.affine_inverse() * p_global_pose;
+	} else {
+		return p_global_pose;
+	}
+}
+
+Transform3D Skeleton3D::local_pose_to_global_pose(int p_bone_idx, Transform3D p_local_pose) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone_idx, bone_size, Transform3D());
+	if (bones[p_bone_idx].parent >= 0) {
+		int parent_bone_idx = bones[p_bone_idx].parent;
+		Transform3D conversion_transform = (bones[parent_bone_idx].pose_global * bones[p_bone_idx].rest);
+		return conversion_transform * p_local_pose;
+	} else {
+		return p_local_pose;
+	}
+}
+
+Basis Skeleton3D::global_pose_z_forward_to_bone_forward(int p_bone_idx, Basis p_basis) {
+	const int bone_size = bones.size();
+	ERR_FAIL_INDEX_V(p_bone_idx, bone_size, Basis());
+	Basis return_basis = p_basis;
+
+	if (bones[p_bone_idx].rest_bone_forward_axis < 0) {
+		update_bone_rest_forward_vector(p_bone_idx, true);
+	}
+
+	if (bones[p_bone_idx].rest_bone_forward_axis == BONE_AXIS_X_FORWARD) {
+		return_basis.rotate_local(Vector3(0, 1, 0), (Math_PI / 2.0));
+	} else if (bones[p_bone_idx].rest_bone_forward_axis == BONE_AXIS_NEGATIVE_X_FORWARD) {
+		return_basis.rotate_local(Vector3(0, 1, 0), -(Math_PI / 2.0));
+	} else if (bones[p_bone_idx].rest_bone_forward_axis == BONE_AXIS_Y_FORWARD) {
+		return_basis.rotate_local(Vector3(1, 0, 0), -(Math_PI / 2.0));
+	} else if (bones[p_bone_idx].rest_bone_forward_axis == BONE_AXIS_NEGATIVE_Y_FORWARD) {
+		return_basis.rotate_local(Vector3(1, 0, 0), (Math_PI / 2.0));
+	} else if (bones[p_bone_idx].rest_bone_forward_axis == BONE_AXIS_Z_FORWARD) {
+		// Do nothing!
+	} else if (bones[p_bone_idx].rest_bone_forward_axis == BONE_AXIS_NEGATIVE_Z_FORWARD) {
+		return_basis.rotate_local(Vector3(0, 0, 1), Math_PI);
+	}
+
+	return return_basis;
+}
+
+// Modifications
+
+#ifndef _3D_DISABLED
+
+void Skeleton3D::set_modification_stack(Ref<SkeletonModificationStack3D> p_stack) {
+	if (modification_stack.is_valid()) {
+		modification_stack->is_setup = false;
+		modification_stack->set_skeleton(nullptr);
+	}
+
+	modification_stack = p_stack;
+	if (modification_stack.is_valid()) {
+		modification_stack->set_skeleton(this);
+		modification_stack->setup();
+	}
+}
+Ref<SkeletonModificationStack3D> Skeleton3D::get_modification_stack() {
+	return modification_stack;
+}
+
+void Skeleton3D::execute_modifications(real_t p_delta, int p_execution_mode) {
+	if (!modification_stack.is_valid()) {
+		return;
+	}
+
+	// Needed to avoid the issue where the stack looses reference to the skeleton when the scene is saved.
+	if (modification_stack->skeleton != this) {
+		modification_stack->set_skeleton(this);
+	}
+
+	modification_stack->execute(p_delta, p_execution_mode);
+}
+
+#endif // _3D_DISABLED
+
 void Skeleton3D::_bind_methods() {
-	ClassDB::bind_method(D_METHOD("get_bone_process_orders"), &Skeleton3D::get_bone_process_orders);
 	ClassDB::bind_method(D_METHOD("add_bone", "name"), &Skeleton3D::add_bone);
 	ClassDB::bind_method(D_METHOD("find_bone", "name"), &Skeleton3D::find_bone);
 	ClassDB::bind_method(D_METHOD("get_bone_name", "bone_idx"), &Skeleton3D::get_bone_name);
@@ -862,6 +1143,13 @@ void Skeleton3D::_bind_methods() {
 
 	ClassDB::bind_method(D_METHOD("unparent_bone_and_rest", "bone_idx"), &Skeleton3D::unparent_bone_and_rest);
 
+	ClassDB::bind_method(D_METHOD("get_bone_children", "bone_idx"), &Skeleton3D::get_bone_children);
+	ClassDB::bind_method(D_METHOD("set_bone_children", "bone_idx", "bone_children"), &Skeleton3D::set_bone_children);
+	ClassDB::bind_method(D_METHOD("add_bone_child", "bone_idx", "child_bone_idx"), &Skeleton3D::add_bone_child);
+	ClassDB::bind_method(D_METHOD("remove_bone_child", "bone_idx", "child_bone_idx"), &Skeleton3D::remove_bone_child);
+
+	ClassDB::bind_method(D_METHOD("get_parentless_bones"), &Skeleton3D::get_parentless_bones);
+
 	ClassDB::bind_method(D_METHOD("get_bone_rest", "bone_idx"), &Skeleton3D::get_bone_rest);
 	ClassDB::bind_method(D_METHOD("set_bone_rest", "bone_idx", "rest"), &Skeleton3D::set_bone_rest);
 
@@ -879,14 +1167,26 @@ void Skeleton3D::_bind_methods() {
 
 	ClassDB::bind_method(D_METHOD("clear_bones_global_pose_override"), &Skeleton3D::clear_bones_global_pose_override);
 	ClassDB::bind_method(D_METHOD("set_bone_global_pose_override", "bone_idx", "pose", "amount", "persistent"), &Skeleton3D::set_bone_global_pose_override, DEFVAL(false));
+	ClassDB::bind_method(D_METHOD("get_bone_global_pose_override", "bone_idx"), &Skeleton3D::get_bone_global_pose_override);
 	ClassDB::bind_method(D_METHOD("get_bone_global_pose", "bone_idx"), &Skeleton3D::get_bone_global_pose);
 	ClassDB::bind_method(D_METHOD("get_bone_global_pose_no_override", "bone_idx"), &Skeleton3D::get_bone_global_pose_no_override);
 
+	ClassDB::bind_method(D_METHOD("clear_bones_local_pose_override"), &Skeleton3D::clear_bones_local_pose_override);
+	ClassDB::bind_method(D_METHOD("set_bone_local_pose_override", "bone_idx", "pose", "amount", "persistent"), &Skeleton3D::set_bone_local_pose_override, DEFVAL(false));
+	ClassDB::bind_method(D_METHOD("get_bone_local_pose_override", "bone_idx"), &Skeleton3D::get_bone_local_pose_override);
+
 	ClassDB::bind_method(D_METHOD("get_bone_custom_pose", "bone_idx"), &Skeleton3D::get_bone_custom_pose);
 	ClassDB::bind_method(D_METHOD("set_bone_custom_pose", "bone_idx", "custom_pose"), &Skeleton3D::set_bone_custom_pose);
 
-	ClassDB::bind_method(D_METHOD("bone_transform_to_world_transform", "bone_transform"), &Skeleton3D::bone_transform_to_world_transform);
-	ClassDB::bind_method(D_METHOD("world_transform_to_bone_transform", "world_transform"), &Skeleton3D::world_transform_to_bone_transform);
+	ClassDB::bind_method(D_METHOD("force_update_all_bone_transforms"), &Skeleton3D::force_update_all_bone_transforms);
+	ClassDB::bind_method(D_METHOD("force_update_bone_child_transform", "bone_idx"), &Skeleton3D::force_update_bone_children_transforms);
+
+	// Helper functions
+	ClassDB::bind_method(D_METHOD("global_pose_to_world_transform", "global_pose"), &Skeleton3D::global_pose_to_world_transform);
+	ClassDB::bind_method(D_METHOD("world_transform_to_global_pose", "world_transform"), &Skeleton3D::world_transform_to_global_pose);
+	ClassDB::bind_method(D_METHOD("global_pose_to_local_pose", "bone_idx", "global_pose"), &Skeleton3D::global_pose_to_local_pose);
+	ClassDB::bind_method(D_METHOD("local_pose_to_global_pose", "bone_idx", "local_pose"), &Skeleton3D::local_pose_to_global_pose);
+	ClassDB::bind_method(D_METHOD("global_pose_z_forward_to_bone_forward", "bone_idx", "basis"), &Skeleton3D::global_pose_z_forward_to_bone_forward);
 
 	ClassDB::bind_method(D_METHOD("set_animate_physical_bones"), &Skeleton3D::set_animate_physical_bones);
 	ClassDB::bind_method(D_METHOD("get_animate_physical_bones"), &Skeleton3D::get_animate_physical_bones);
@@ -896,12 +1196,21 @@ void Skeleton3D::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("physical_bones_add_collision_exception", "exception"), &Skeleton3D::physical_bones_add_collision_exception);
 	ClassDB::bind_method(D_METHOD("physical_bones_remove_collision_exception", "exception"), &Skeleton3D::physical_bones_remove_collision_exception);
 
+	// Modifications
+	ClassDB::bind_method(D_METHOD("set_modification_stack", "modification_stack"), &Skeleton3D::set_modification_stack);
+	ClassDB::bind_method(D_METHOD("get_modification_stack"), &Skeleton3D::get_modification_stack);
+	ClassDB::bind_method(D_METHOD("execute_modifications", "delta", "execution_mode"), &Skeleton3D::execute_modifications);
+
+#ifndef _3D_DISABLED
 	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "animate_physical_bones"), "set_animate_physical_bones", "get_animate_physical_bones");
+#endif // _3D_DISABLED
 
 #ifdef TOOLS_ENABLED
 	ADD_SIGNAL(MethodInfo("pose_updated"));
 #endif // TOOLS_ENABLED
 
+	ADD_SIGNAL(MethodInfo("bone_pose_changed", PropertyInfo(Variant::INT, "bone_idx")));
+
 	BIND_CONSTANT(NOTIFICATION_UPDATE_SKELETON);
 }
 

scene/3d/skeleton_3d.h

@@ -32,6 +32,7 @@
 #define SKELETON_3D_H
 
 #include "scene/3d/node_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
 #include "scene/resources/skin.h"
 
 typedef int BoneId;
@@ -61,6 +62,8 @@ public:
 	~SkinReference();
 };
 
+class SkeletonModificationStack3D;
+
 class Skeleton3D : public Node3D {
 	GDCLASS(Skeleton3D, Node3D);
 
@@ -70,9 +73,8 @@ private:
 	struct Bone {
 		String name;
 
-		bool enabled = true;
-		int parent = -1;
-		int sort_index = 0; //used for re-sorting process order
+		bool enabled;
+		int parent;
 
 		bool disable_rest = false;
 		Transform3D rest;
@@ -91,7 +93,35 @@ private:
 		PhysicalBone3D *physical_bone = nullptr;
 		PhysicalBone3D *cache_parent_physical_bone = nullptr;
 
-		List<ObjectID> nodes_bound;
+		real_t local_pose_override_amount;
+		bool local_pose_override_reset;
+		Transform3D local_pose_override;
+
+		Vector<int> child_bones;
+
+		// The forward direction vector and rest bone forward axis are cached because they do not change
+		// 99% of the time, but recalculating them can be expensive on models with many bones.
+		Vector3 rest_bone_forward_vector;
+		int rest_bone_forward_axis = -1;
+
+		Bone() {
+			parent = -1;
+			enabled = true;
+			disable_rest = false;
+			custom_pose_enable = false;
+			global_pose_override_amount = 0;
+			global_pose_override_reset = false;
+#ifndef _3D_DISABLED
+			physical_bone = nullptr;
+			cache_parent_physical_bone = nullptr;
+#endif // _3D_DISABLED
+			local_pose_override_amount = 0;
+			local_pose_override_reset = false;
+			child_bones = Vector<int>();
+
+			rest_bone_forward_vector = Vector3(0, 0, 0);
+			rest_bone_forward_axis = -1;
+		}
 	};
 
 	Set<SkinReference *> skin_bindings;
@@ -100,8 +130,9 @@ private:
 
 	bool animate_physical_bones = true;
 	Vector<Bone> bones;
-	Vector<int> process_order;
-	bool process_order_dirty = true;
+	bool process_order_dirty;
+
+	Vector<int> parentless_bones;
 
 	void _make_dirty();
 	bool dirty = false;
@@ -117,7 +148,20 @@ protected:
 	void _notification(int p_what);
 	static void _bind_methods();
 
+#ifndef _3D_DISABLED
+	Ref<SkeletonModificationStack3D> modification_stack;
+#endif // _3D_DISABLED
+
 public:
+	enum Bone_Forward_Axis {
+		BONE_AXIS_X_FORWARD = 0,
+		BONE_AXIS_Y_FORWARD = 1,
+		BONE_AXIS_Z_FORWARD = 2,
+		BONE_AXIS_NEGATIVE_X_FORWARD = 3,
+		BONE_AXIS_NEGATIVE_Y_FORWARD = 4,
+		BONE_AXIS_NEGATIVE_Z_FORWARD = 5,
+	};
+
 	enum {
 		NOTIFICATION_UPDATE_SKELETON = 50
 	};
@@ -135,6 +179,12 @@ public:
 
 	void unparent_bone_and_rest(int p_bone);
 
+	Vector<int> get_bone_children(int p_bone);
+	void set_bone_children(int p_bone, Vector<int> p_children);
+	void add_bone_child(int p_bone, int p_child);
+	void remove_bone_child(int p_bone, int p_child);
+	Vector<int> get_parentless_bones();
+
 	void set_bone_disable_rest(int p_bone, bool p_disable);
 	bool is_bone_rest_disabled(int p_bone) const;
 
@@ -145,16 +195,8 @@ public:
 	Transform3D get_bone_global_pose(int p_bone) const;
 	Transform3D get_bone_global_pose_no_override(int p_bone) const;
 
-	void clear_bones_global_pose_override();
-	void set_bone_global_pose_override(int p_bone, const Transform3D &p_pose, real_t p_amount, bool p_persistent = false);
-
 	void set_bone_enabled(int p_bone, bool p_enabled);
 	bool is_bone_enabled(int p_bone) const;
-
-	void bind_child_node_to_bone(int p_bone, Node *p_node);
-	void unbind_child_node_from_bone(int p_bone, Node *p_node);
-	void get_bound_child_nodes_to_bone(int p_bone, List<Node *> *p_bound) const;
-
 	void clear_bones();
 
 	// posing api
@@ -165,15 +207,40 @@ public:
 	void set_bone_custom_pose(int p_bone, const Transform3D &p_custom_pose);
 	Transform3D get_bone_custom_pose(int p_bone) const;
 
+	void clear_bones_global_pose_override();
+	Transform3D get_bone_global_pose_override(int p_bone) const;
+	void set_bone_global_pose_override(int p_bone, const Transform3D &p_pose, real_t p_amount, bool p_persistent = false);
+
+	void clear_bones_local_pose_override();
+	Transform3D get_bone_local_pose_override(int p_bone) const;
+	void set_bone_local_pose_override(int p_bone, const Transform3D &p_pose, real_t p_amount, bool p_persistent = false);
+
 	void localize_rests(); // used for loaders and tools
-	int get_process_order(int p_idx);
-	Vector<int> get_bone_process_orders();
 
 	Ref<SkinReference> register_skin(const Ref<Skin> &p_skin);
 
+	void force_update_all_bone_transforms();
+	void force_update_bone_children_transforms(int bone_idx);
+
+	void update_bone_rest_forward_vector(int p_bone, bool p_force_update = false);
+	void update_bone_rest_forward_axis(int p_bone, bool p_force_update = false);
+	Vector3 get_bone_axis_forward_vector(int p_bone);
+	int get_bone_axis_forward_enum(int p_bone);
+
 	// Helper functions
-	Transform3D bone_transform_to_world_transform(Transform3D p_transform);
-	Transform3D world_transform_to_bone_transform(Transform3D p_transform);
+	Transform3D global_pose_to_world_transform(Transform3D p_global_pose);
+	Transform3D world_transform_to_global_pose(Transform3D p_transform);
+	Transform3D global_pose_to_local_pose(int p_bone_idx, Transform3D p_global_pose);
+	Transform3D local_pose_to_global_pose(int p_bone_idx, Transform3D p_local_pose);
+
+	Basis global_pose_z_forward_to_bone_forward(int p_bone_idx, Basis p_basis);
+
+	// Modifications
+#ifndef _3D_DISABLED
+	Ref<SkeletonModificationStack3D> get_modification_stack();
+	void set_modification_stack(Ref<SkeletonModificationStack3D> p_stack);
+	void execute_modifications(real_t p_delta, int p_execution_mode);
+#endif // _3D_DISABLED
 
 	// Physical bone API
 

scene/register_scene_types.cpp

@@ -168,7 +168,15 @@
 #include "scene/resources/skeleton_modification_2d_physicalbones.h"
 #include "scene/resources/skeleton_modification_2d_stackholder.h"
 #include "scene/resources/skeleton_modification_2d_twoboneik.h"
+#include "scene/resources/skeleton_modification_3d.h"
+#include "scene/resources/skeleton_modification_3d_ccdik.h"
+#include "scene/resources/skeleton_modification_3d_fabrik.h"
+#include "scene/resources/skeleton_modification_3d_jiggle.h"
+#include "scene/resources/skeleton_modification_3d_lookat.h"
+#include "scene/resources/skeleton_modification_3d_stackholder.h"
+#include "scene/resources/skeleton_modification_3d_twoboneik.h"
 #include "scene/resources/skeleton_modification_stack_2d.h"
+#include "scene/resources/skeleton_modification_stack_3d.h"
 #include "scene/resources/sky.h"
 #include "scene/resources/sky_material.h"
 #include "scene/resources/sphere_shape_3d.h"
@@ -754,6 +762,15 @@ void register_scene_types() {
 	GDREGISTER_CLASS(ConvexPolygonShape3D);
 	GDREGISTER_CLASS(ConcavePolygonShape3D);
 
+	ClassDB::register_class<SkeletonModificationStack3D>();
+	ClassDB::register_class<SkeletonModification3D>();
+	ClassDB::register_class<SkeletonModification3DLookAt>();
+	ClassDB::register_class<SkeletonModification3DCCDIK>();
+	ClassDB::register_class<SkeletonModification3DFABRIK>();
+	ClassDB::register_class<SkeletonModification3DJiggle>();
+	ClassDB::register_class<SkeletonModification3DTwoBoneIK>();
+	ClassDB::register_class<SkeletonModification3DStackHolder>();
+
 	OS::get_singleton()->yield(); //may take time to init
 
 	GDREGISTER_CLASS(VelocityTracker3D);

scene/resources/skeleton_modification_3d.cpp

@@ -0,0 +1,170 @@
+/*************************************************************************/
+/*  skeleton_modification_3d.cpp                                         */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "skeleton_modification_3d.h"
+#include "scene/3d/skeleton_3d.h"
+
+void SkeletonModification3D::_execute(real_t p_delta) {
+	if (get_script_instance()) {
+		if (get_script_instance()->has_method("execute")) {
+			get_script_instance()->call("execute", p_delta);
+		}
+	}
+
+	if (!enabled)
+		return;
+}
+
+void SkeletonModification3D::_setup_modification(SkeletonModificationStack3D *p_stack) {
+	stack = p_stack;
+	if (stack) {
+		is_setup = true;
+	} else {
+		WARN_PRINT("Could not setup modification with name " + this->get_name());
+	}
+
+	if (get_script_instance()) {
+		if (get_script_instance()->has_method("setup_modification")) {
+			get_script_instance()->call("setup_modification", p_stack);
+		}
+	}
+}
+
+void SkeletonModification3D::set_enabled(bool p_enabled) {
+	enabled = p_enabled;
+}
+
+bool SkeletonModification3D::get_enabled() {
+	return enabled;
+}
+
+// Helper function. Needed for CCDIK.
+real_t SkeletonModification3D::clamp_angle(real_t p_angle, real_t p_min_bound, real_t p_max_bound, bool p_invert) {
+	// Map to the 0 to 360 range (in radians though) instead of the -180 to 180 range.
+	if (p_angle < 0) {
+		p_angle = Math_TAU + p_angle;
+	}
+
+	// Make min and max in the range of 0 to 360 (in radians), and make sure they are in the right order
+	if (p_min_bound < 0) {
+		p_min_bound = Math_TAU + p_min_bound;
+	}
+	if (p_max_bound < 0) {
+		p_max_bound = Math_TAU + p_max_bound;
+	}
+	if (p_min_bound > p_max_bound) {
+		real_t tmp = p_min_bound;
+		p_min_bound = p_max_bound;
+		p_max_bound = tmp;
+	}
+
+	// Note: May not be the most optimal way to clamp, but it always constraints to the nearest angle.
+	if (p_invert == false) {
+		if (p_angle < p_min_bound || p_angle > p_max_bound) {
+			Vector2 min_bound_vec = Vector2(Math::cos(p_min_bound), Math::sin(p_min_bound));
+			Vector2 max_bound_vec = Vector2(Math::cos(p_max_bound), Math::sin(p_max_bound));
+			Vector2 angle_vec = Vector2(Math::cos(p_angle), Math::sin(p_angle));
+
+			if (angle_vec.distance_squared_to(min_bound_vec) <= angle_vec.distance_squared_to(max_bound_vec)) {
+				p_angle = p_min_bound;
+			} else {
+				p_angle = p_max_bound;
+			}
+		}
+	} else {
+		if (p_angle > p_min_bound && p_angle < p_max_bound) {
+			Vector2 min_bound_vec = Vector2(Math::cos(p_min_bound), Math::sin(p_min_bound));
+			Vector2 max_bound_vec = Vector2(Math::cos(p_max_bound), Math::sin(p_max_bound));
+			Vector2 angle_vec = Vector2(Math::cos(p_angle), Math::sin(p_angle));
+
+			if (angle_vec.distance_squared_to(min_bound_vec) <= angle_vec.distance_squared_to(max_bound_vec)) {
+				p_angle = p_min_bound;
+			} else {
+				p_angle = p_max_bound;
+			}
+		}
+	}
+	return p_angle;
+}
+
+bool SkeletonModification3D::_print_execution_error(bool p_condition, String p_message) {
+	// If the modification is not setup, don't bother printing the error
+	if (!is_setup) {
+		return p_condition;
+	}
+
+	if (p_condition && !execution_error_found) {
+		ERR_PRINT(p_message);
+		execution_error_found = true;
+	}
+	return p_condition;
+}
+
+Ref<SkeletonModificationStack3D> SkeletonModification3D::get_modification_stack() {
+	return stack;
+}
+
+void SkeletonModification3D::set_is_setup(bool p_is_setup) {
+	is_setup = p_is_setup;
+}
+
+bool SkeletonModification3D::get_is_setup() const {
+	return is_setup;
+}
+
+void SkeletonModification3D::set_execution_mode(int p_mode) {
+	execution_mode = p_mode;
+}
+
+int SkeletonModification3D::get_execution_mode() const {
+	return execution_mode;
+}
+
+void SkeletonModification3D::_bind_methods() {
+	BIND_VMETHOD(MethodInfo("_execute", PropertyInfo(Variant::FLOAT, "delta")));
+	BIND_VMETHOD(MethodInfo("_setup_modification", PropertyInfo(Variant::OBJECT, "modification_stack", PROPERTY_HINT_RESOURCE_TYPE, "SkeletonModificationStack3D")));
+
+	ClassDB::bind_method(D_METHOD("set_enabled", "enabled"), &SkeletonModification3D::set_enabled);
+	ClassDB::bind_method(D_METHOD("get_enabled"), &SkeletonModification3D::get_enabled);
+	ClassDB::bind_method(D_METHOD("get_modification_stack"), &SkeletonModification3D::get_modification_stack);
+	ClassDB::bind_method(D_METHOD("set_is_setup", "is_setup"), &SkeletonModification3D::set_is_setup);
+	ClassDB::bind_method(D_METHOD("get_is_setup"), &SkeletonModification3D::get_is_setup);
+	ClassDB::bind_method(D_METHOD("set_execution_mode", "execution_mode"), &SkeletonModification3D::set_execution_mode);
+	ClassDB::bind_method(D_METHOD("get_execution_mode"), &SkeletonModification3D::get_execution_mode);
+	ClassDB::bind_method(D_METHOD("clamp_angle", "angle", "min", "max", "invert"), &SkeletonModification3D::clamp_angle);
+
+	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "enabled"), "set_enabled", "get_enabled");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "execution_mode", PROPERTY_HINT_ENUM, "process, physics_process"), "set_execution_mode", "get_execution_mode");
+}
+
+SkeletonModification3D::SkeletonModification3D() {
+	stack = nullptr;
+	is_setup = false;
+}

scene/resources/skeleton_modification_3d.h

@@ -0,0 +1,76 @@
+/*************************************************************************/
+/*  skeleton_modification_3d.h                                           */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef SKELETONMODIFICATION3D_H
+#define SKELETONMODIFICATION3D_H
+
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_stack_3d.h"
+
+class SkeletonModificationStack3D;
+
+class SkeletonModification3D : public Resource {
+	GDCLASS(SkeletonModification3D, Resource);
+	friend class Skeleton3D;
+	friend class SkeletonModificationStack3D;
+
+protected:
+	static void _bind_methods();
+
+	SkeletonModificationStack3D *stack;
+	int execution_mode = 0; // 0 = process
+
+	bool enabled = true;
+	bool is_setup = false;
+	bool execution_error_found = false;
+
+	bool _print_execution_error(bool p_condition, String p_message);
+
+public:
+	virtual void _execute(real_t p_delta);
+	virtual void _setup_modification(SkeletonModificationStack3D *p_stack);
+
+	real_t clamp_angle(real_t p_angle, real_t p_min_bound, real_t p_max_bound, bool p_invert);
+
+	void set_enabled(bool p_enabled);
+	bool get_enabled();
+
+	void set_execution_mode(int p_mode);
+	int get_execution_mode() const;
+
+	Ref<SkeletonModificationStack3D> get_modification_stack();
+
+	void set_is_setup(bool p_setup);
+	bool get_is_setup() const;
+
+	SkeletonModification3D();
+};
+
+#endif // SKELETONMODIFICATION3D_H

scene/resources/skeleton_modification_3d_ccdik.cpp

@@ -0,0 +1,474 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_ccdik.cpp                                   */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "scene/resources/skeleton_modification_3d_ccdik.h"
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+bool SkeletonModification3DCCDIK::_set(const StringName &p_path, const Variant &p_value) {
+	String path = p_path;
+
+	if (path.begins_with("joint_data/")) {
+		int ccdik_data_size = ccdik_data_chain.size();
+		int which = path.get_slicec('/', 1).to_int();
+		String what = path.get_slicec('/', 2);
+		ERR_FAIL_INDEX_V(which, ccdik_data_size, false);
+
+		if (what == "bone_name") {
+			set_ccdik_joint_bone_name(which, p_value);
+		} else if (what == "bone_index") {
+			set_ccdik_joint_bone_index(which, p_value);
+		} else if (what == "ccdik_axis") {
+			set_ccdik_joint_ccdik_axis(which, p_value);
+		} else if (what == "enable_joint_constraint") {
+			set_ccdik_joint_enable_constraint(which, p_value);
+		} else if (what == "joint_constraint_angle_min") {
+			set_ccdik_joint_constraint_angle_min(which, Math::deg2rad(real_t(p_value)));
+		} else if (what == "joint_constraint_angle_max") {
+			set_ccdik_joint_constraint_angle_max(which, Math::deg2rad(real_t(p_value)));
+		} else if (what == "joint_constraint_angles_invert") {
+			set_ccdik_joint_constraint_invert(which, p_value);
+		}
+		return true;
+	}
+	return true;
+}
+
+bool SkeletonModification3DCCDIK::_get(const StringName &p_path, Variant &r_ret) const {
+	String path = p_path;
+
+	if (path.begins_with("joint_data/")) {
+		const int ccdik_data_size = ccdik_data_chain.size();
+		int which = path.get_slicec('/', 1).to_int();
+		String what = path.get_slicec('/', 2);
+		ERR_FAIL_INDEX_V(which, ccdik_data_size, false);
+
+		if (what == "bone_name") {
+			r_ret = get_ccdik_joint_bone_name(which);
+		} else if (what == "bone_index") {
+			r_ret = get_ccdik_joint_bone_index(which);
+		} else if (what == "ccdik_axis") {
+			r_ret = get_ccdik_joint_ccdik_axis(which);
+		} else if (what == "enable_joint_constraint") {
+			r_ret = get_ccdik_joint_enable_constraint(which);
+		} else if (what == "joint_constraint_angle_min") {
+			r_ret = Math::rad2deg(get_ccdik_joint_constraint_angle_min(which));
+		} else if (what == "joint_constraint_angle_max") {
+			r_ret = Math::rad2deg(get_ccdik_joint_constraint_angle_max(which));
+		} else if (what == "joint_constraint_angles_invert") {
+			r_ret = get_ccdik_joint_constraint_invert(which);
+		}
+		return true;
+	}
+	return true;
+}
+
+void SkeletonModification3DCCDIK::_get_property_list(List<PropertyInfo> *p_list) const {
+	for (uint32_t i = 0; i < ccdik_data_chain.size(); i++) {
+		String base_string = "joint_data/" + itos(i) + "/";
+
+		p_list->push_back(PropertyInfo(Variant::STRING_NAME, base_string + "bone_name", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+		p_list->push_back(PropertyInfo(Variant::INT, base_string + "bone_index", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+
+		p_list->push_back(PropertyInfo(Variant::INT, base_string + "ccdik_axis",
+				PROPERTY_HINT_ENUM, "X Axis, Y Axis, Z Axis", PROPERTY_USAGE_DEFAULT));
+
+		p_list->push_back(PropertyInfo(Variant::BOOL, base_string + "enable_joint_constraint", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+		if (ccdik_data_chain[i].enable_constraint) {
+			p_list->push_back(PropertyInfo(Variant::FLOAT, base_string + "joint_constraint_angle_min", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+			p_list->push_back(PropertyInfo(Variant::FLOAT, base_string + "joint_constraint_angle_max", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+			p_list->push_back(PropertyInfo(Variant::BOOL, base_string + "joint_constraint_angles_invert", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+		}
+	}
+}
+
+void SkeletonModification3DCCDIK::_execute(real_t p_delta) {
+	ERR_FAIL_COND_MSG(!stack || !is_setup || stack->skeleton == nullptr,
+			"Modification is not setup and therefore cannot execute!");
+	if (!enabled) {
+		return;
+	}
+
+	if (target_node_cache.is_null()) {
+		_print_execution_error(true, "Target cache is out of date. Attempting to update");
+		update_target_cache();
+		return;
+	}
+	if (tip_node_cache.is_null()) {
+		_print_execution_error(true, "Tip cache is out of date. Attempting to update");
+		update_tip_cache();
+		return;
+	}
+
+	// Reset the local bone overrides for CCDIK affected nodes
+	for (uint32_t i = 0; i < ccdik_data_chain.size(); i++) {
+		stack->skeleton->set_bone_local_pose_override(ccdik_data_chain[i].bone_idx,
+				stack->skeleton->get_bone_local_pose_override(ccdik_data_chain[i].bone_idx),
+				0.0, false);
+	}
+
+	Node3D *node_target = Object::cast_to<Node3D>(ObjectDB::get_instance(target_node_cache));
+	Node3D *node_tip = Object::cast_to<Node3D>(ObjectDB::get_instance(tip_node_cache));
+
+	if (_print_execution_error(!node_target || !node_target->is_inside_tree(), "Target node is not in the scene tree. Cannot execute modification!")) {
+		return;
+	}
+	if (_print_execution_error(!node_tip || !node_tip->is_inside_tree(), "Tip node is not in the scene tree. Cannot execute modification!")) {
+		return;
+	}
+
+	if (use_high_quality_solve) {
+		for (uint32_t i = 0; i < ccdik_data_chain.size(); i++) {
+			for (uint32_t j = i; j < ccdik_data_chain.size(); j++) {
+				_execute_ccdik_joint(j, node_target, node_tip);
+			}
+		}
+	} else {
+		for (uint32_t i = 0; i < ccdik_data_chain.size(); i++) {
+			_execute_ccdik_joint(i, node_target, node_tip);
+		}
+	}
+
+	execution_error_found = false;
+}
+
+void SkeletonModification3DCCDIK::_execute_ccdik_joint(int p_joint_idx, Node3D *p_target, Node3D *p_tip) {
+	CCDIK_Joint_Data ccdik_data = ccdik_data_chain[p_joint_idx];
+
+	if (_print_execution_error(ccdik_data.bone_idx < 0 || ccdik_data.bone_idx > stack->skeleton->get_bone_count(),
+				"CCDIK joint: bone index for joint" + itos(p_joint_idx) + " not found. Cannot execute modification!")) {
+		return;
+	}
+
+	Transform3D bone_trans = stack->skeleton->global_pose_to_local_pose(ccdik_data.bone_idx, stack->skeleton->get_bone_global_pose(ccdik_data.bone_idx));
+	Transform3D tip_trans = stack->skeleton->global_pose_to_local_pose(ccdik_data.bone_idx, stack->skeleton->world_transform_to_global_pose(p_tip->get_global_transform()));
+	Transform3D target_trans = stack->skeleton->global_pose_to_local_pose(ccdik_data.bone_idx, stack->skeleton->world_transform_to_global_pose(p_target->get_global_transform()));
+
+	if (tip_trans.origin.distance_to(target_trans.origin) <= 0.01) {
+		return;
+	}
+
+	// Inspired (and very loosely based on) by the CCDIK algorithm made by Zalo on GitHub (https://github.com/zalo/MathUtilities)
+	// Convert the 3D position to a 2D position so we can use Atan2 (via the angle function)
+	// to know how much rotation we need on the given axis to place the tip at the target.
+	Vector2 tip_pos_2d;
+	Vector2 target_pos_2d;
+	if (ccdik_data.ccdik_axis == CCDIK_Axes::AXIS_X) {
+		tip_pos_2d = Vector2(tip_trans.origin.y, tip_trans.origin.z);
+		target_pos_2d = Vector2(target_trans.origin.y, target_trans.origin.z);
+		bone_trans.basis.rotate_local(Vector3(1, 0, 0), target_pos_2d.angle() - tip_pos_2d.angle());
+	} else if (ccdik_data.ccdik_axis == CCDIK_Axes::AXIS_Y) {
+		tip_pos_2d = Vector2(tip_trans.origin.z, tip_trans.origin.x);
+		target_pos_2d = Vector2(target_trans.origin.z, target_trans.origin.x);
+		bone_trans.basis.rotate_local(Vector3(0, 1, 0), target_pos_2d.angle() - tip_pos_2d.angle());
+	} else if (ccdik_data.ccdik_axis == CCDIK_Axes::AXIS_Z) {
+		tip_pos_2d = Vector2(tip_trans.origin.x, tip_trans.origin.y);
+		target_pos_2d = Vector2(target_trans.origin.x, target_trans.origin.y);
+		bone_trans.basis.rotate_local(Vector3(0, 0, 1), target_pos_2d.angle() - tip_pos_2d.angle());
+	} else {
+		// Should never happen, but...
+		ERR_FAIL_MSG("CCDIK joint: Unknown axis vector passed for joint" + itos(p_joint_idx) + ". Cannot execute modification!");
+	}
+
+	if (ccdik_data.enable_constraint) {
+		Vector3 rotation_axis;
+		real_t rotation_angle;
+		bone_trans.basis.get_axis_angle(rotation_axis, rotation_angle);
+
+		// Note: When the axis has a negative direction, the angle is OVER 180 degrees and therefore we need to account for this
+		// when constraining.
+		if (ccdik_data.ccdik_axis == CCDIK_Axes::AXIS_X) {
+			if (rotation_axis.x < 0) {
+				rotation_angle += Math_PI;
+				rotation_axis = Vector3(1, 0, 0);
+			}
+		} else if (ccdik_data.ccdik_axis == CCDIK_Axes::AXIS_Y) {
+			if (rotation_axis.y < 0) {
+				rotation_angle += Math_PI;
+				rotation_axis = Vector3(0, 1, 0);
+			}
+		} else if (ccdik_data.ccdik_axis == CCDIK_Axes::AXIS_Z) {
+			if (rotation_axis.z < 0) {
+				rotation_angle += Math_PI;
+				rotation_axis = Vector3(0, 0, 1);
+			}
+		} else {
+			// Should never happen, but...
+			ERR_FAIL_MSG("CCDIK joint: Unknown axis vector passed for joint" + itos(p_joint_idx) + ". Cannot execute modification!");
+		}
+		rotation_angle = clamp_angle(rotation_angle, ccdik_data.constraint_angle_min, ccdik_data.constraint_angle_max, ccdik_data.constraint_angles_invert);
+
+		bone_trans.basis.set_axis_angle(rotation_axis, rotation_angle);
+	}
+
+	stack->skeleton->set_bone_local_pose_override(ccdik_data.bone_idx, bone_trans, stack->strength, true);
+	stack->skeleton->force_update_bone_children_transforms(ccdik_data.bone_idx);
+}
+
+void SkeletonModification3DCCDIK::_setup_modification(SkeletonModificationStack3D *p_stack) {
+	stack = p_stack;
+	if (stack != nullptr) {
+		is_setup = true;
+		execution_error_found = false;
+		update_target_cache();
+		update_tip_cache();
+	}
+}
+
+void SkeletonModification3DCCDIK::update_target_cache() {
+	if (!is_setup || !stack) {
+		_print_execution_error(true, "Cannot update target cache: modification is not properly setup!");
+		return;
+	}
+
+	target_node_cache = ObjectID();
+	if (stack->skeleton) {
+		if (stack->skeleton->is_inside_tree()) {
+			if (stack->skeleton->has_node(target_node)) {
+				Node *node = stack->skeleton->get_node(target_node);
+				ERR_FAIL_COND_MSG(!node || stack->skeleton == node,
+						"Cannot update target cache: node is this modification's skeleton or cannot be found!");
+				ERR_FAIL_COND_MSG(!node->is_inside_tree(),
+						"Cannot update target cache: node is not in scene tree!");
+				target_node_cache = node->get_instance_id();
+
+				execution_error_found = false;
+			}
+		}
+	}
+}
+
+void SkeletonModification3DCCDIK::update_tip_cache() {
+	if (!is_setup || !stack) {
+		_print_execution_error(true, "Cannot update tip cache: modification is not properly setup!");
+		return;
+	}
+
+	tip_node_cache = ObjectID();
+	if (stack->skeleton) {
+		if (stack->skeleton->is_inside_tree()) {
+			if (stack->skeleton->has_node(tip_node)) {
+				Node *node = stack->skeleton->get_node(tip_node);
+				ERR_FAIL_COND_MSG(!node || stack->skeleton == node,
+						"Cannot update tip cache: node is this modification's skeleton or cannot be found!");
+				ERR_FAIL_COND_MSG(!node->is_inside_tree(),
+						"Cannot update tip cache: node is not in scene tree!");
+				tip_node_cache = node->get_instance_id();
+
+				execution_error_found = false;
+			}
+		}
+	}
+}
+
+void SkeletonModification3DCCDIK::set_target_node(const NodePath &p_target_node) {
+	target_node = p_target_node;
+	update_target_cache();
+}
+
+NodePath SkeletonModification3DCCDIK::get_target_node() const {
+	return target_node;
+}
+
+void SkeletonModification3DCCDIK::set_tip_node(const NodePath &p_tip_node) {
+	tip_node = p_tip_node;
+	update_tip_cache();
+}
+
+NodePath SkeletonModification3DCCDIK::get_tip_node() const {
+	return tip_node;
+}
+
+void SkeletonModification3DCCDIK::set_use_high_quality_solve(bool p_high_quality) {
+	use_high_quality_solve = p_high_quality;
+}
+
+bool SkeletonModification3DCCDIK::get_use_high_quality_solve() const {
+	return use_high_quality_solve;
+}
+
+// CCDIK joint data functions
+String SkeletonModification3DCCDIK::get_ccdik_joint_bone_name(int p_joint_idx) const {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, String());
+	return ccdik_data_chain[p_joint_idx].bone_name;
+}
+
+void SkeletonModification3DCCDIK::set_ccdik_joint_bone_name(int p_joint_idx, String p_bone_name) {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	ccdik_data_chain[p_joint_idx].bone_name = p_bone_name;
+
+	if (stack) {
+		if (stack->skeleton) {
+			ccdik_data_chain[p_joint_idx].bone_idx = stack->skeleton->find_bone(p_bone_name);
+		}
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+int SkeletonModification3DCCDIK::get_ccdik_joint_bone_index(int p_joint_idx) const {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, -1);
+	return ccdik_data_chain[p_joint_idx].bone_idx;
+}
+
+void SkeletonModification3DCCDIK::set_ccdik_joint_bone_index(int p_joint_idx, int p_bone_idx) {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	ERR_FAIL_COND_MSG(p_bone_idx < 0, "Bone index is out of range: The index is too low!");
+	ccdik_data_chain[p_joint_idx].bone_idx = p_bone_idx;
+
+	if (stack) {
+		if (stack->skeleton) {
+			ccdik_data_chain[p_joint_idx].bone_name = stack->skeleton->get_bone_name(p_bone_idx);
+		}
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+int SkeletonModification3DCCDIK::get_ccdik_joint_ccdik_axis(int p_joint_idx) const {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, -1);
+	return ccdik_data_chain[p_joint_idx].ccdik_axis;
+}
+
+void SkeletonModification3DCCDIK::set_ccdik_joint_ccdik_axis(int p_joint_idx, int p_axis) {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	ERR_FAIL_COND_MSG(p_axis < 0, "CCDIK axis is out of range: The axis mode is too low!");
+	ccdik_data_chain[p_joint_idx].ccdik_axis = p_axis;
+	notify_property_list_changed();
+}
+
+bool SkeletonModification3DCCDIK::get_ccdik_joint_enable_constraint(int p_joint_idx) const {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, false);
+	return ccdik_data_chain[p_joint_idx].enable_constraint;
+}
+
+void SkeletonModification3DCCDIK::set_ccdik_joint_enable_constraint(int p_joint_idx, bool p_enable) {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	ccdik_data_chain[p_joint_idx].enable_constraint = p_enable;
+	notify_property_list_changed();
+}
+
+real_t SkeletonModification3DCCDIK::get_ccdik_joint_constraint_angle_min(int p_joint_idx) const {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, false);
+	return ccdik_data_chain[p_joint_idx].constraint_angle_min;
+}
+
+void SkeletonModification3DCCDIK::set_ccdik_joint_constraint_angle_min(int p_joint_idx, real_t p_angle_min) {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	ccdik_data_chain[p_joint_idx].constraint_angle_min = p_angle_min;
+}
+
+real_t SkeletonModification3DCCDIK::get_ccdik_joint_constraint_angle_max(int p_joint_idx) const {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, false);
+	return ccdik_data_chain[p_joint_idx].constraint_angle_max;
+}
+
+void SkeletonModification3DCCDIK::set_ccdik_joint_constraint_angle_max(int p_joint_idx, real_t p_angle_max) {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	ccdik_data_chain[p_joint_idx].constraint_angle_max = p_angle_max;
+}
+
+bool SkeletonModification3DCCDIK::get_ccdik_joint_constraint_invert(int p_joint_idx) const {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, false);
+	return ccdik_data_chain[p_joint_idx].constraint_angles_invert;
+}
+
+void SkeletonModification3DCCDIK::set_ccdik_joint_constraint_invert(int p_joint_idx, bool p_invert) {
+	const int bone_chain_size = ccdik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	ccdik_data_chain[p_joint_idx].constraint_angles_invert = p_invert;
+}
+
+int SkeletonModification3DCCDIK::get_ccdik_data_chain_length() {
+	return ccdik_data_chain.size();
+}
+void SkeletonModification3DCCDIK::set_ccdik_data_chain_length(int p_length) {
+	ERR_FAIL_COND(p_length < 0);
+	ccdik_data_chain.resize(p_length);
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+void SkeletonModification3DCCDIK::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("set_target_node", "target_nodepath"), &SkeletonModification3DCCDIK::set_target_node);
+	ClassDB::bind_method(D_METHOD("get_target_node"), &SkeletonModification3DCCDIK::get_target_node);
+
+	ClassDB::bind_method(D_METHOD("set_tip_node", "tip_nodepath"), &SkeletonModification3DCCDIK::set_tip_node);
+	ClassDB::bind_method(D_METHOD("get_tip_node"), &SkeletonModification3DCCDIK::get_tip_node);
+
+	ClassDB::bind_method(D_METHOD("set_use_high_quality_solve", "high_quality_solve"), &SkeletonModification3DCCDIK::set_use_high_quality_solve);
+	ClassDB::bind_method(D_METHOD("get_use_high_quality_solve"), &SkeletonModification3DCCDIK::get_use_high_quality_solve);
+
+	// CCDIK joint data functions
+	ClassDB::bind_method(D_METHOD("get_ccdik_joint_bone_name", "joint_idx"), &SkeletonModification3DCCDIK::get_ccdik_joint_bone_name);
+	ClassDB::bind_method(D_METHOD("set_ccdik_joint_bone_name", "joint_idx", "bone_name"), &SkeletonModification3DCCDIK::set_ccdik_joint_bone_name);
+	ClassDB::bind_method(D_METHOD("get_ccdik_joint_bone_index", "joint_idx"), &SkeletonModification3DCCDIK::get_ccdik_joint_bone_index);
+	ClassDB::bind_method(D_METHOD("set_ccdik_joint_bone_index", "joint_idx", "bone_index"), &SkeletonModification3DCCDIK::set_ccdik_joint_bone_index);
+	ClassDB::bind_method(D_METHOD("get_ccdik_joint_ccdik_axis", "joint_idx"), &SkeletonModification3DCCDIK::get_ccdik_joint_ccdik_axis);
+	ClassDB::bind_method(D_METHOD("set_ccdik_joint_ccdik_axis", "joint_idx", "axis"), &SkeletonModification3DCCDIK::set_ccdik_joint_ccdik_axis);
+	ClassDB::bind_method(D_METHOD("get_ccdik_joint_enable_joint_constraint", "joint_idx"), &SkeletonModification3DCCDIK::get_ccdik_joint_enable_constraint);
+	ClassDB::bind_method(D_METHOD("set_ccdik_joint_enable_joint_constraint", "joint_idx", "enable"), &SkeletonModification3DCCDIK::set_ccdik_joint_enable_constraint);
+	ClassDB::bind_method(D_METHOD("get_ccdik_joint_constraint_angle_min", "joint_idx"), &SkeletonModification3DCCDIK::get_ccdik_joint_constraint_angle_min);
+	ClassDB::bind_method(D_METHOD("set_ccdik_joint_constraint_angle_min", "joint_idx", "min_angle"), &SkeletonModification3DCCDIK::set_ccdik_joint_constraint_angle_min);
+	ClassDB::bind_method(D_METHOD("get_ccdik_joint_constraint_angle_max", "joint_idx"), &SkeletonModification3DCCDIK::get_ccdik_joint_constraint_angle_max);
+	ClassDB::bind_method(D_METHOD("set_ccdik_joint_constraint_angle_max", "joint_idx", "max_angle"), &SkeletonModification3DCCDIK::set_ccdik_joint_constraint_angle_max);
+	ClassDB::bind_method(D_METHOD("get_ccdik_joint_constraint_invert", "joint_idx"), &SkeletonModification3DCCDIK::get_ccdik_joint_constraint_invert);
+	ClassDB::bind_method(D_METHOD("set_ccdik_joint_constraint_invert", "joint_idx", "invert"), &SkeletonModification3DCCDIK::set_ccdik_joint_constraint_invert);
+
+	ClassDB::bind_method(D_METHOD("set_ccdik_data_chain_length", "length"), &SkeletonModification3DCCDIK::set_ccdik_data_chain_length);
+	ClassDB::bind_method(D_METHOD("get_ccdik_data_chain_length"), &SkeletonModification3DCCDIK::get_ccdik_data_chain_length);
+
+	ADD_PROPERTY(PropertyInfo(Variant::NODE_PATH, "target_nodepath", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "Node3D"), "set_target_node", "get_target_node");
+	ADD_PROPERTY(PropertyInfo(Variant::NODE_PATH, "tip_nodepath", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "Node3D"), "set_tip_node", "get_tip_node");
+	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "high_quality_solve", PROPERTY_HINT_NONE, ""), "set_use_high_quality_solve", "get_use_high_quality_solve");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "ccdik_data_chain_length", PROPERTY_HINT_RANGE, "0,100,1"), "set_ccdik_data_chain_length", "get_ccdik_data_chain_length");
+}
+
+SkeletonModification3DCCDIK::SkeletonModification3DCCDIK() {
+	stack = nullptr;
+	is_setup = false;
+	enabled = true;
+}
+
+SkeletonModification3DCCDIK::~SkeletonModification3DCCDIK() {
+}

scene/resources/skeleton_modification_3d_ccdik.h

@@ -0,0 +1,114 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_ccdik.h                                     */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "core/templates/local_vector.h"
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+#ifndef SKELETONMODIFICATION3DCCDIK_H
+#define SKELETONMODIFICATION3DCCDIK_H
+
+class SkeletonModification3DCCDIK : public SkeletonModification3D {
+	GDCLASS(SkeletonModification3DCCDIK, SkeletonModification3D);
+
+private:
+	enum CCDIK_Axes {
+		AXIS_X,
+		AXIS_Y,
+		AXIS_Z
+	};
+
+	struct CCDIK_Joint_Data {
+		String bone_name = "";
+		int bone_idx = -1;
+		int ccdik_axis = 0;
+
+		bool enable_constraint = false;
+		real_t constraint_angle_min = 0;
+		real_t constraint_angle_max = (2.0 * Math_PI);
+		bool constraint_angles_invert = false;
+	};
+
+	LocalVector<CCDIK_Joint_Data> ccdik_data_chain;
+	NodePath target_node;
+	ObjectID target_node_cache;
+
+	NodePath tip_node;
+	ObjectID tip_node_cache;
+
+	bool use_high_quality_solve = true;
+
+	void update_target_cache();
+	void update_tip_cache();
+
+	void _execute_ccdik_joint(int p_joint_idx, Node3D *p_target, Node3D *p_tip);
+
+protected:
+	static void _bind_methods();
+	bool _get(const StringName &p_path, Variant &r_ret) const;
+	bool _set(const StringName &p_path, const Variant &p_value);
+	void _get_property_list(List<PropertyInfo> *p_list) const;
+
+public:
+	virtual void _execute(real_t p_delta) override;
+	virtual void _setup_modification(SkeletonModificationStack3D *p_stack) override;
+
+	void set_target_node(const NodePath &p_target_node);
+	NodePath get_target_node() const;
+
+	void set_tip_node(const NodePath &p_tip_node);
+	NodePath get_tip_node() const;
+
+	void set_use_high_quality_solve(bool p_solve);
+	bool get_use_high_quality_solve() const;
+
+	String get_ccdik_joint_bone_name(int p_joint_idx) const;
+	void set_ccdik_joint_bone_name(int p_joint_idx, String p_bone_name);
+	int get_ccdik_joint_bone_index(int p_joint_idx) const;
+	void set_ccdik_joint_bone_index(int p_joint_idx, int p_bone_idx);
+	int get_ccdik_joint_ccdik_axis(int p_joint_idx) const;
+	void set_ccdik_joint_ccdik_axis(int p_joint_idx, int p_axis);
+	bool get_ccdik_joint_enable_constraint(int p_joint_idx) const;
+	void set_ccdik_joint_enable_constraint(int p_joint_idx, bool p_enable);
+	real_t get_ccdik_joint_constraint_angle_min(int p_joint_idx) const;
+	void set_ccdik_joint_constraint_angle_min(int p_joint_idx, real_t p_angle_min);
+	real_t get_ccdik_joint_constraint_angle_max(int p_joint_idx) const;
+	void set_ccdik_joint_constraint_angle_max(int p_joint_idx, real_t p_angle_max);
+	bool get_ccdik_joint_constraint_invert(int p_joint_idx) const;
+	void set_ccdik_joint_constraint_invert(int p_joint_idx, bool p_invert);
+
+	int get_ccdik_data_chain_length();
+	void set_ccdik_data_chain_length(int p_new_length);
+
+	SkeletonModification3DCCDIK();
+	~SkeletonModification3DCCDIK();
+};
+
+#endif //SKELETONMODIFICATION3DCCDIK_H

scene/resources/skeleton_modification_3d_fabrik.cpp

@@ -0,0 +1,628 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_fabrik.cpp                                  */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "scene/resources/skeleton_modification_3d_fabrik.h"
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+bool SkeletonModification3DFABRIK::_set(const StringName &p_path, const Variant &p_value) {
+	String path = p_path;
+
+	if (path.begins_with("joint_data/")) {
+		int fabrik_data_size = fabrik_data_chain.size();
+		int which = path.get_slicec('/', 1).to_int();
+		String what = path.get_slicec('/', 2);
+		ERR_FAIL_INDEX_V(which, fabrik_data_size, false);
+
+		if (what == "bone_name") {
+			set_fabrik_joint_bone_name(which, p_value);
+		} else if (what == "bone_index") {
+			set_fabrik_joint_bone_index(which, p_value);
+		} else if (what == "length") {
+			set_fabrik_joint_length(which, p_value);
+		} else if (what == "magnet_position") {
+			set_fabrik_joint_magnet(which, p_value);
+		} else if (what == "auto_calculate_length") {
+			set_fabrik_joint_auto_calculate_length(which, p_value);
+		} else if (what == "use_tip_node") {
+			set_fabrik_joint_use_tip_node(which, p_value);
+		} else if (what == "tip_node") {
+			set_fabrik_joint_tip_node(which, p_value);
+		} else if (what == "use_target_basis") {
+			set_fabrik_joint_use_target_basis(which, p_value);
+		} else if (what == "roll") {
+			set_fabrik_joint_roll(which, Math::deg2rad(real_t(p_value)));
+		}
+		return true;
+	}
+	return true;
+}
+
+bool SkeletonModification3DFABRIK::_get(const StringName &p_path, Variant &r_ret) const {
+	String path = p_path;
+
+	if (path.begins_with("joint_data/")) {
+		const int fabrik_data_size = fabrik_data_chain.size();
+		int which = path.get_slicec('/', 1).to_int();
+		String what = path.get_slicec('/', 2);
+		ERR_FAIL_INDEX_V(which, fabrik_data_size, false);
+
+		if (what == "bone_name") {
+			r_ret = get_fabrik_joint_bone_name(which);
+		} else if (what == "bone_index") {
+			r_ret = get_fabrik_joint_bone_index(which);
+		} else if (what == "length") {
+			r_ret = get_fabrik_joint_length(which);
+		} else if (what == "magnet_position") {
+			r_ret = get_fabrik_joint_magnet(which);
+		} else if (what == "auto_calculate_length") {
+			r_ret = get_fabrik_joint_auto_calculate_length(which);
+		} else if (what == "use_tip_node") {
+			r_ret = get_fabrik_joint_use_tip_node(which);
+		} else if (what == "tip_node") {
+			r_ret = get_fabrik_joint_tip_node(which);
+		} else if (what == "use_target_basis") {
+			r_ret = get_fabrik_joint_use_target_basis(which);
+		} else if (what == "roll") {
+			r_ret = Math::rad2deg(get_fabrik_joint_roll(which));
+		}
+		return true;
+	}
+	return true;
+}
+
+void SkeletonModification3DFABRIK::_get_property_list(List<PropertyInfo> *p_list) const {
+	for (uint32_t i = 0; i < fabrik_data_chain.size(); i++) {
+		String base_string = "joint_data/" + itos(i) + "/";
+
+		p_list->push_back(PropertyInfo(Variant::STRING_NAME, base_string + "bone_name", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+		p_list->push_back(PropertyInfo(Variant::INT, base_string + "bone_index", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+		p_list->push_back(PropertyInfo(Variant::FLOAT, base_string + "roll", PROPERTY_HINT_RANGE, "-360,360,0.01", PROPERTY_USAGE_DEFAULT));
+		p_list->push_back(PropertyInfo(Variant::BOOL, base_string + "auto_calculate_length", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+
+		if (!fabrik_data_chain[i].auto_calculate_length) {
+			p_list->push_back(PropertyInfo(Variant::FLOAT, base_string + "length", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+		} else {
+			p_list->push_back(PropertyInfo(Variant::BOOL, base_string + "use_tip_node", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+			if (fabrik_data_chain[i].use_tip_node) {
+				p_list->push_back(PropertyInfo(Variant::NODE_PATH, base_string + "tip_node", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "Node3D", PROPERTY_USAGE_DEFAULT));
+			}
+		}
+
+		// Cannot apply magnet to the origin of the chain, as it will not do anything.
+		if (i > 0) {
+			p_list->push_back(PropertyInfo(Variant::VECTOR3, base_string + "magnet_position", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+		}
+		// Only give the override basis option on the last bone in the chain, so only include it for the last bone.
+		if (i == fabrik_data_chain.size() - 1) {
+			p_list->push_back(PropertyInfo(Variant::BOOL, base_string + "use_target_basis", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+		}
+	}
+}
+
+void SkeletonModification3DFABRIK::_execute(real_t p_delta) {
+	ERR_FAIL_COND_MSG(!stack || !is_setup || stack->skeleton == nullptr,
+			"Modification is not setup and therefore cannot execute!");
+	if (!enabled) {
+		return;
+	}
+
+	if (target_node_cache.is_null()) {
+		_print_execution_error(true, "Target cache is out of date. Attempting to update...");
+		update_target_cache();
+		return;
+	}
+
+	if (_print_execution_error(fabrik_data_chain.size() <= 1, "FABRIK requires at least two joints to operate. Cannot execute modification!")) {
+		return;
+	}
+
+	Node3D *node_target = Object::cast_to<Node3D>(ObjectDB::get_instance(target_node_cache));
+	if (_print_execution_error(!node_target || !node_target->is_inside_tree(), "Target node is not in the scene tree. Cannot execute modification!")) {
+		return;
+	}
+
+	// Verify that all joints have a valid bone ID, and that all bone lengths are zero or more
+	// Also, while we are here, apply magnet positions.
+	for (uint32_t i = 0; i < fabrik_data_chain.size(); i++) {
+		if (_print_execution_error(fabrik_data_chain[i].bone_idx < 0, "FABRIK Joint " + itos(i) + " has an invalid bone ID. Cannot execute!")) {
+			return;
+		}
+
+		if (fabrik_data_chain[i].length < 0 && fabrik_data_chain[i].auto_calculate_length) {
+			fabrik_joint_auto_calculate_length(i);
+		}
+		if (_print_execution_error(fabrik_data_chain[i].length < 0, "FABRIK Joint " + itos(i) + " has an invalid joint length. Cannot execute!")) {
+			return;
+		}
+
+		Transform3D local_pose_override = stack->skeleton->get_bone_local_pose_override(fabrik_data_chain[i].bone_idx);
+
+		// Apply magnet positions:
+		if (stack->skeleton->get_bone_parent(fabrik_data_chain[i].bone_idx) >= 0) {
+			int parent_bone_idx = stack->skeleton->get_bone_parent(fabrik_data_chain[i].bone_idx);
+			Transform3D conversion_transform = (stack->skeleton->get_bone_global_pose(parent_bone_idx) * stack->skeleton->get_bone_rest(parent_bone_idx));
+			local_pose_override.origin += conversion_transform.basis.xform_inv(fabrik_data_chain[i].magnet_position);
+		} else {
+			local_pose_override.origin += fabrik_data_chain[i].magnet_position;
+		}
+
+		stack->skeleton->set_bone_local_pose_override(fabrik_data_chain[i].bone_idx, local_pose_override, stack->strength, true);
+	}
+
+	target_global_pose = stack->skeleton->world_transform_to_global_pose(node_target->get_global_transform());
+	origin_global_pose = stack->skeleton->local_pose_to_global_pose(
+			fabrik_data_chain[0].bone_idx, stack->skeleton->get_bone_local_pose_override(fabrik_data_chain[0].bone_idx));
+
+	final_joint_idx = fabrik_data_chain.size() - 1;
+	real_t target_distance = stack->skeleton->global_pose_to_local_pose(fabrik_data_chain[final_joint_idx].bone_idx, target_global_pose).origin.length();
+	chain_iterations = 0;
+
+	while (target_distance > chain_tolerance) {
+		chain_backwards();
+		chain_forwards();
+
+		// update the target distance
+		target_distance = stack->skeleton->global_pose_to_local_pose(fabrik_data_chain[final_joint_idx].bone_idx, target_global_pose).origin.length();
+
+		// update chain iterations
+		chain_iterations += 1;
+		if (chain_iterations >= chain_max_iterations) {
+			break;
+		}
+	}
+	chain_apply();
+
+	execution_error_found = false;
+}
+
+void SkeletonModification3DFABRIK::chain_backwards() {
+	int final_bone_idx = fabrik_data_chain[final_joint_idx].bone_idx;
+	Transform3D final_joint_trans = stack->skeleton->local_pose_to_global_pose(final_bone_idx, stack->skeleton->get_bone_local_pose_override(final_bone_idx));
+
+	// Get the direction the final bone is facing in.
+	stack->skeleton->update_bone_rest_forward_vector(final_bone_idx);
+	Transform3D final_bone_direction_trans = final_joint_trans.looking_at(target_global_pose.origin, Vector3(0, 1, 0));
+	final_bone_direction_trans.basis = stack->skeleton->global_pose_z_forward_to_bone_forward(final_bone_idx, final_bone_direction_trans.basis);
+	Vector3 direction = final_bone_direction_trans.basis.xform(stack->skeleton->get_bone_axis_forward_vector(final_bone_idx)).normalized();
+
+	// If set to override, then use the target's Basis rather than the bone's
+	if (fabrik_data_chain[final_joint_idx].use_target_basis) {
+		direction = target_global_pose.basis.xform(stack->skeleton->get_bone_axis_forward_vector(final_bone_idx)).normalized();
+	}
+
+	// set the position of the final joint to the target position
+	final_joint_trans.origin = target_global_pose.origin - (direction * fabrik_data_chain[final_joint_idx].length);
+	final_joint_trans = stack->skeleton->global_pose_to_local_pose(final_bone_idx, final_joint_trans);
+	stack->skeleton->set_bone_local_pose_override(final_bone_idx, final_joint_trans, stack->strength, true);
+
+	// for all other joints, move them towards the target
+	int i = final_joint_idx;
+	while (i >= 1) {
+		int next_bone_idx = fabrik_data_chain[i].bone_idx;
+		Transform3D next_bone_trans = stack->skeleton->local_pose_to_global_pose(next_bone_idx, stack->skeleton->get_bone_local_pose_override(next_bone_idx));
+		i -= 1;
+		int current_bone_idx = fabrik_data_chain[i].bone_idx;
+		Transform3D current_trans = stack->skeleton->local_pose_to_global_pose(current_bone_idx, stack->skeleton->get_bone_local_pose_override(current_bone_idx));
+
+		real_t length = fabrik_data_chain[i].length / (next_bone_trans.origin - current_trans.origin).length();
+		current_trans.origin = next_bone_trans.origin.lerp(current_trans.origin, length);
+
+		// Apply it back to the skeleton
+		stack->skeleton->set_bone_local_pose_override(current_bone_idx, stack->skeleton->global_pose_to_local_pose(current_bone_idx, current_trans), stack->strength, true);
+	}
+}
+
+void SkeletonModification3DFABRIK::chain_forwards() {
+	// Set root at the initial position.
+	int origin_bone_idx = fabrik_data_chain[0].bone_idx;
+	Transform3D root_transform = stack->skeleton->local_pose_to_global_pose(origin_bone_idx, stack->skeleton->get_bone_local_pose_override(origin_bone_idx));
+	root_transform.origin = origin_global_pose.origin;
+	stack->skeleton->set_bone_local_pose_override(origin_bone_idx, stack->skeleton->global_pose_to_local_pose(origin_bone_idx, root_transform), stack->strength, true);
+
+	for (uint32_t i = 0; i < fabrik_data_chain.size() - 1; i++) {
+		int current_bone_idx = fabrik_data_chain[i].bone_idx;
+		Transform3D current_trans = stack->skeleton->local_pose_to_global_pose(current_bone_idx, stack->skeleton->get_bone_local_pose_override(current_bone_idx));
+		int next_bone_idx = fabrik_data_chain[i + 1].bone_idx;
+		Transform3D next_bone_trans = stack->skeleton->local_pose_to_global_pose(next_bone_idx, stack->skeleton->get_bone_local_pose_override(next_bone_idx));
+
+		real_t length = fabrik_data_chain[i].length / (current_trans.origin - next_bone_trans.origin).length();
+		next_bone_trans.origin = current_trans.origin.lerp(next_bone_trans.origin, length);
+
+		// Apply it back to the skeleton
+		stack->skeleton->set_bone_local_pose_override(next_bone_idx, stack->skeleton->global_pose_to_local_pose(next_bone_idx, next_bone_trans), stack->strength, true);
+	}
+}
+
+void SkeletonModification3DFABRIK::chain_apply() {
+	for (uint32_t i = 0; i < fabrik_data_chain.size(); i++) {
+		int current_bone_idx = fabrik_data_chain[i].bone_idx;
+		Transform3D current_trans = stack->skeleton->get_bone_local_pose_override(current_bone_idx);
+		current_trans = stack->skeleton->local_pose_to_global_pose(current_bone_idx, current_trans);
+
+		// If this is the last bone in the chain...
+		if (i == fabrik_data_chain.size() - 1) {
+			if (fabrik_data_chain[i].use_target_basis == false) { // Point to target...
+				// Get the forward direction that the basis is facing in right now.
+				stack->skeleton->update_bone_rest_forward_vector(current_bone_idx);
+				Vector3 forward_vector = stack->skeleton->get_bone_axis_forward_vector(current_bone_idx);
+				// Rotate the bone towards the target:
+				current_trans.basis.rotate_to_align(forward_vector, current_trans.origin.direction_to(target_global_pose.origin));
+				current_trans.basis.rotate_local(forward_vector, fabrik_data_chain[i].roll);
+			} else { // Use the target's Basis...
+				current_trans.basis = target_global_pose.basis.orthonormalized().scaled(current_trans.basis.get_scale());
+			}
+		} else { // every other bone in the chain...
+			int next_bone_idx = fabrik_data_chain[i + 1].bone_idx;
+			Transform3D next_trans = stack->skeleton->local_pose_to_global_pose(next_bone_idx, stack->skeleton->get_bone_local_pose_override(next_bone_idx));
+
+			// Get the forward direction that the basis is facing in right now.
+			stack->skeleton->update_bone_rest_forward_vector(current_bone_idx);
+			Vector3 forward_vector = stack->skeleton->get_bone_axis_forward_vector(current_bone_idx);
+			// Rotate the bone towards the next bone in the chain:
+			current_trans.basis.rotate_to_align(forward_vector, current_trans.origin.direction_to(next_trans.origin));
+			current_trans.basis.rotate_local(forward_vector, fabrik_data_chain[i].roll);
+		}
+		current_trans = stack->skeleton->global_pose_to_local_pose(current_bone_idx, current_trans);
+		current_trans.origin = Vector3(0, 0, 0);
+		stack->skeleton->set_bone_local_pose_override(current_bone_idx, current_trans, stack->strength, true);
+	}
+
+	// Update all the bones so the next modification has up-to-date data.
+	stack->skeleton->force_update_all_bone_transforms();
+}
+
+void SkeletonModification3DFABRIK::_setup_modification(SkeletonModificationStack3D *p_stack) {
+	stack = p_stack;
+	if (stack != nullptr) {
+		is_setup = true;
+		execution_error_found = false;
+		update_target_cache();
+
+		for (uint32_t i = 0; i < fabrik_data_chain.size(); i++) {
+			update_joint_tip_cache(i);
+		}
+	}
+}
+
+void SkeletonModification3DFABRIK::update_target_cache() {
+	if (!is_setup || !stack) {
+		_print_execution_error(true, "Cannot update target cache: modification is not properly setup!");
+		return;
+	}
+	target_node_cache = ObjectID();
+	if (stack->skeleton) {
+		if (stack->skeleton->is_inside_tree() && target_node.is_empty() == false) {
+			if (stack->skeleton->has_node(target_node)) {
+				Node *node = stack->skeleton->get_node(target_node);
+				ERR_FAIL_COND_MSG(!node || stack->skeleton == node,
+						"Cannot update target cache: node is this modification's skeleton or cannot be found!");
+				ERR_FAIL_COND_MSG(!node->is_inside_tree(),
+						"Cannot update target cache: node is not in the scene tree!");
+				target_node_cache = node->get_instance_id();
+
+				execution_error_found = false;
+			}
+		}
+	}
+}
+
+void SkeletonModification3DFABRIK::update_joint_tip_cache(int p_joint_idx) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX_MSG(p_joint_idx, bone_chain_size, "FABRIK joint not found");
+	if (!is_setup || !stack) {
+		_print_execution_error(true, "Cannot update tip cache: modification is not properly setup!");
+		return;
+	}
+	fabrik_data_chain[p_joint_idx].tip_node_cache = ObjectID();
+	if (stack->skeleton) {
+		if (stack->skeleton->is_inside_tree() && fabrik_data_chain[p_joint_idx].tip_node.is_empty() == false) {
+			if (stack->skeleton->has_node(fabrik_data_chain[p_joint_idx].tip_node)) {
+				Node *node = stack->skeleton->get_node(fabrik_data_chain[p_joint_idx].tip_node);
+				ERR_FAIL_COND_MSG(!node || stack->skeleton == node,
+						"Cannot update tip cache for joint " + itos(p_joint_idx) + ": node is this modification's skeleton or cannot be found!");
+				ERR_FAIL_COND_MSG(!node->is_inside_tree(),
+						"Cannot update tip cache for joint " + itos(p_joint_idx) + ": node is not in scene tree!");
+				fabrik_data_chain[p_joint_idx].tip_node_cache = node->get_instance_id();
+
+				execution_error_found = false;
+			}
+		}
+	}
+}
+
+void SkeletonModification3DFABRIK::set_target_node(const NodePath &p_target_node) {
+	target_node = p_target_node;
+	update_target_cache();
+}
+
+NodePath SkeletonModification3DFABRIK::get_target_node() const {
+	return target_node;
+}
+
+int SkeletonModification3DFABRIK::get_fabrik_data_chain_length() {
+	return fabrik_data_chain.size();
+}
+
+void SkeletonModification3DFABRIK::set_fabrik_data_chain_length(int p_length) {
+	ERR_FAIL_COND(p_length < 0);
+	fabrik_data_chain.resize(p_length);
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+real_t SkeletonModification3DFABRIK::get_chain_tolerance() {
+	return chain_tolerance;
+}
+
+void SkeletonModification3DFABRIK::set_chain_tolerance(real_t p_tolerance) {
+	ERR_FAIL_COND_MSG(p_tolerance <= 0, "FABRIK chain tolerance must be more than zero!");
+	chain_tolerance = p_tolerance;
+}
+
+int SkeletonModification3DFABRIK::get_chain_max_iterations() {
+	return chain_max_iterations;
+}
+void SkeletonModification3DFABRIK::set_chain_max_iterations(int p_iterations) {
+	ERR_FAIL_COND_MSG(p_iterations <= 0, "FABRIK chain iterations must be at least one. Set enabled to false to disable the FABRIK chain.");
+	chain_max_iterations = p_iterations;
+}
+
+// FABRIK joint data functions
+String SkeletonModification3DFABRIK::get_fabrik_joint_bone_name(int p_joint_idx) const {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, String());
+	return fabrik_data_chain[p_joint_idx].bone_name;
+}
+
+void SkeletonModification3DFABRIK::set_fabrik_joint_bone_name(int p_joint_idx, String p_bone_name) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	fabrik_data_chain[p_joint_idx].bone_name = p_bone_name;
+
+	if (stack) {
+		if (stack->skeleton) {
+			fabrik_data_chain[p_joint_idx].bone_idx = stack->skeleton->find_bone(p_bone_name);
+		}
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+int SkeletonModification3DFABRIK::get_fabrik_joint_bone_index(int p_joint_idx) const {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, -1);
+	return fabrik_data_chain[p_joint_idx].bone_idx;
+}
+
+void SkeletonModification3DFABRIK::set_fabrik_joint_bone_index(int p_joint_idx, int p_bone_idx) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	ERR_FAIL_COND_MSG(p_bone_idx < 0, "Bone index is out of range: The index is too low!");
+	fabrik_data_chain[p_joint_idx].bone_idx = p_bone_idx;
+
+	if (stack) {
+		if (stack->skeleton) {
+			fabrik_data_chain[p_joint_idx].bone_name = stack->skeleton->get_bone_name(p_bone_idx);
+		}
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+real_t SkeletonModification3DFABRIK::get_fabrik_joint_length(int p_joint_idx) const {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, -1);
+	return fabrik_data_chain[p_joint_idx].length;
+}
+
+void SkeletonModification3DFABRIK::set_fabrik_joint_length(int p_joint_idx, real_t p_bone_length) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	ERR_FAIL_COND_MSG(p_bone_length < 0, "FABRIK joint length cannot be less than zero!");
+
+	if (!is_setup) {
+		fabrik_data_chain[p_joint_idx].length = p_bone_length;
+		return;
+	}
+
+	if (fabrik_data_chain[p_joint_idx].auto_calculate_length) {
+		WARN_PRINT("FABRIK Length not set: auto calculate length is enabled for this joint!");
+		fabrik_joint_auto_calculate_length(p_joint_idx);
+	} else {
+		fabrik_data_chain[p_joint_idx].length = p_bone_length;
+	}
+
+	execution_error_found = false;
+}
+
+Vector3 SkeletonModification3DFABRIK::get_fabrik_joint_magnet(int p_joint_idx) const {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, Vector3());
+	return fabrik_data_chain[p_joint_idx].magnet_position;
+}
+
+void SkeletonModification3DFABRIK::set_fabrik_joint_magnet(int p_joint_idx, Vector3 p_magnet) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	fabrik_data_chain[p_joint_idx].magnet_position = p_magnet;
+}
+
+bool SkeletonModification3DFABRIK::get_fabrik_joint_auto_calculate_length(int p_joint_idx) const {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, false);
+	return fabrik_data_chain[p_joint_idx].auto_calculate_length;
+}
+
+void SkeletonModification3DFABRIK::set_fabrik_joint_auto_calculate_length(int p_joint_idx, bool p_auto_calculate) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	fabrik_data_chain[p_joint_idx].auto_calculate_length = p_auto_calculate;
+	fabrik_joint_auto_calculate_length(p_joint_idx);
+	notify_property_list_changed();
+}
+
+void SkeletonModification3DFABRIK::fabrik_joint_auto_calculate_length(int p_joint_idx) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	if (!fabrik_data_chain[p_joint_idx].auto_calculate_length) {
+		return;
+	}
+
+	if (!stack || !stack->skeleton || !is_setup) {
+		_print_execution_error(true, "Cannot auto calculate joint length: modification is not properly setup!");
+		return;
+	}
+	ERR_FAIL_INDEX_MSG(fabrik_data_chain[p_joint_idx].bone_idx, stack->skeleton->get_bone_count(),
+			"Bone for joint " + itos(p_joint_idx) + " is not set or points to an unknown bone!");
+
+	if (fabrik_data_chain[p_joint_idx].use_tip_node) { // Use the tip node to update joint length.
+
+		update_joint_tip_cache(p_joint_idx);
+
+		Node3D *tip_node = Object::cast_to<Node3D>(ObjectDB::get_instance(fabrik_data_chain[p_joint_idx].tip_node_cache));
+		ERR_FAIL_COND_MSG(!tip_node, "Tip node for joint " + itos(p_joint_idx) + "is not a Node3D-based node. Cannot calculate length...");
+		ERR_FAIL_COND_MSG(!tip_node->is_inside_tree(), "Tip node for joint " + itos(p_joint_idx) + "is not in the scene tree. Cannot calculate length...");
+
+		Transform3D node_trans = tip_node->get_global_transform();
+		node_trans = stack->skeleton->world_transform_to_global_pose(node_trans);
+		node_trans = stack->skeleton->global_pose_to_local_pose(fabrik_data_chain[p_joint_idx].bone_idx, node_trans);
+		fabrik_data_chain[p_joint_idx].length = node_trans.origin.length();
+	} else { // Use child bone(s) to update joint length, if possible
+		Vector<int> bone_children = stack->skeleton->get_bone_children(fabrik_data_chain[p_joint_idx].bone_idx);
+		if (bone_children.size() <= 0) {
+			ERR_FAIL_MSG("Cannot calculate length for joint " + itos(p_joint_idx) + "joint uses leaf bone. \nPlease manually set the bone length or use a tip node!");
+			return;
+		}
+
+		real_t final_length = 0;
+		for (int i = 0; i < bone_children.size(); i++) {
+			Transform3D child_transform = stack->skeleton->get_bone_global_pose(bone_children[i]);
+			final_length += stack->skeleton->global_pose_to_local_pose(fabrik_data_chain[p_joint_idx].bone_idx, child_transform).origin.length();
+		}
+		fabrik_data_chain[p_joint_idx].length = final_length / bone_children.size();
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+bool SkeletonModification3DFABRIK::get_fabrik_joint_use_tip_node(int p_joint_idx) const {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, false);
+	return fabrik_data_chain[p_joint_idx].use_tip_node;
+}
+
+void SkeletonModification3DFABRIK::set_fabrik_joint_use_tip_node(int p_joint_idx, bool p_use_tip_node) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	fabrik_data_chain[p_joint_idx].use_tip_node = p_use_tip_node;
+	notify_property_list_changed();
+}
+
+NodePath SkeletonModification3DFABRIK::get_fabrik_joint_tip_node(int p_joint_idx) const {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, NodePath());
+	return fabrik_data_chain[p_joint_idx].tip_node;
+}
+
+void SkeletonModification3DFABRIK::set_fabrik_joint_tip_node(int p_joint_idx, NodePath p_tip_node) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	fabrik_data_chain[p_joint_idx].tip_node = p_tip_node;
+	update_joint_tip_cache(p_joint_idx);
+}
+
+bool SkeletonModification3DFABRIK::get_fabrik_joint_use_target_basis(int p_joint_idx) const {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, false);
+	return fabrik_data_chain[p_joint_idx].use_target_basis;
+}
+
+void SkeletonModification3DFABRIK::set_fabrik_joint_use_target_basis(int p_joint_idx, bool p_use_target_basis) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	fabrik_data_chain[p_joint_idx].use_target_basis = p_use_target_basis;
+}
+
+real_t SkeletonModification3DFABRIK::get_fabrik_joint_roll(int p_joint_idx) const {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, 0.0);
+	return fabrik_data_chain[p_joint_idx].roll;
+}
+
+void SkeletonModification3DFABRIK::set_fabrik_joint_roll(int p_joint_idx, real_t p_roll) {
+	const int bone_chain_size = fabrik_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	fabrik_data_chain[p_joint_idx].roll = p_roll;
+}
+
+void SkeletonModification3DFABRIK::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("set_target_node", "target_nodepath"), &SkeletonModification3DFABRIK::set_target_node);
+	ClassDB::bind_method(D_METHOD("get_target_node"), &SkeletonModification3DFABRIK::get_target_node);
+	ClassDB::bind_method(D_METHOD("set_fabrik_data_chain_length", "length"), &SkeletonModification3DFABRIK::set_fabrik_data_chain_length);
+	ClassDB::bind_method(D_METHOD("get_fabrik_data_chain_length"), &SkeletonModification3DFABRIK::get_fabrik_data_chain_length);
+	ClassDB::bind_method(D_METHOD("set_chain_tolerance", "tolerance"), &SkeletonModification3DFABRIK::set_chain_tolerance);
+	ClassDB::bind_method(D_METHOD("get_chain_tolerance"), &SkeletonModification3DFABRIK::get_chain_tolerance);
+	ClassDB::bind_method(D_METHOD("set_chain_max_iterations", "max_iterations"), &SkeletonModification3DFABRIK::set_chain_max_iterations);
+	ClassDB::bind_method(D_METHOD("get_chain_max_iterations"), &SkeletonModification3DFABRIK::get_chain_max_iterations);
+
+	// FABRIK joint data functions
+	ClassDB::bind_method(D_METHOD("get_fabrik_joint_bone_name", "joint_idx"), &SkeletonModification3DFABRIK::get_fabrik_joint_bone_name);
+	ClassDB::bind_method(D_METHOD("set_fabrik_joint_bone_name", "joint_idx", "bone_name"), &SkeletonModification3DFABRIK::set_fabrik_joint_bone_name);
+	ClassDB::bind_method(D_METHOD("get_fabrik_joint_bone_index", "joint_idx"), &SkeletonModification3DFABRIK::get_fabrik_joint_bone_index);
+	ClassDB::bind_method(D_METHOD("set_fabrik_joint_bone_index", "joint_idx", "bone_index"), &SkeletonModification3DFABRIK::set_fabrik_joint_bone_index);
+	ClassDB::bind_method(D_METHOD("get_fabrik_joint_length", "joint_idx"), &SkeletonModification3DFABRIK::get_fabrik_joint_length);
+	ClassDB::bind_method(D_METHOD("set_fabrik_joint_length", "joint_idx", "length"), &SkeletonModification3DFABRIK::set_fabrik_joint_length);
+	ClassDB::bind_method(D_METHOD("get_fabrik_joint_magnet", "joint_idx"), &SkeletonModification3DFABRIK::get_fabrik_joint_magnet);
+	ClassDB::bind_method(D_METHOD("set_fabrik_joint_magnet", "joint_idx", "magnet_position"), &SkeletonModification3DFABRIK::set_fabrik_joint_magnet);
+	ClassDB::bind_method(D_METHOD("get_fabrik_joint_auto_calculate_length", "joint_idx"), &SkeletonModification3DFABRIK::get_fabrik_joint_auto_calculate_length);
+	ClassDB::bind_method(D_METHOD("set_fabrik_joint_auto_calculate_length", "joint_idx", "auto_calculate_length"), &SkeletonModification3DFABRIK::set_fabrik_joint_auto_calculate_length);
+	ClassDB::bind_method(D_METHOD("fabrik_joint_auto_calculate_length", "joint_idx"), &SkeletonModification3DFABRIK::fabrik_joint_auto_calculate_length);
+	ClassDB::bind_method(D_METHOD("get_fabrik_joint_use_tip_node", "joint_idx"), &SkeletonModification3DFABRIK::get_fabrik_joint_use_tip_node);
+	ClassDB::bind_method(D_METHOD("set_fabrik_joint_use_tip_node", "joint_idx", "use_tip_node"), &SkeletonModification3DFABRIK::set_fabrik_joint_use_tip_node);
+	ClassDB::bind_method(D_METHOD("get_fabrik_joint_tip_node", "joint_idx"), &SkeletonModification3DFABRIK::get_fabrik_joint_tip_node);
+	ClassDB::bind_method(D_METHOD("set_fabrik_joint_tip_node", "joint_idx", "tip_node"), &SkeletonModification3DFABRIK::set_fabrik_joint_tip_node);
+	ClassDB::bind_method(D_METHOD("get_fabrik_joint_use_target_basis", "joint_idx"), &SkeletonModification3DFABRIK::get_fabrik_joint_use_target_basis);
+	ClassDB::bind_method(D_METHOD("set_fabrik_joint_use_target_basis", "joint_idx", "use_target_basis"), &SkeletonModification3DFABRIK::set_fabrik_joint_use_target_basis);
+
+	ADD_PROPERTY(PropertyInfo(Variant::NODE_PATH, "target_nodepath", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "Node3D"), "set_target_node", "get_target_node");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "fabrik_data_chain_length", PROPERTY_HINT_RANGE, "0,100,1"), "set_fabrik_data_chain_length", "get_fabrik_data_chain_length");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "chain_tolerance", PROPERTY_HINT_RANGE, "0,100,0.001"), "set_chain_tolerance", "get_chain_tolerance");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "chain_max_iterations", PROPERTY_HINT_RANGE, "1,50,1"), "set_chain_max_iterations", "get_chain_max_iterations");
+}
+
+SkeletonModification3DFABRIK::SkeletonModification3DFABRIK() {
+	stack = nullptr;
+	is_setup = false;
+	enabled = true;
+}
+
+SkeletonModification3DFABRIK::~SkeletonModification3DFABRIK() {
+}

scene/resources/skeleton_modification_3d_fabrik.h

@@ -0,0 +1,122 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_fabrik.h                                    */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "core/templates/local_vector.h"
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+#ifndef SKELETONMODIFICATION3DFABRIK_H
+#define SKELETONMODIFICATION3DFABRIK_H
+
+class SkeletonModification3DFABRIK : public SkeletonModification3D {
+	GDCLASS(SkeletonModification3DFABRIK, SkeletonModification3D);
+
+private:
+	struct FABRIK_Joint_Data {
+		String bone_name = "";
+		int bone_idx = -1;
+		real_t length = -1;
+		Vector3 magnet_position = Vector3(0, 0, 0);
+
+		bool auto_calculate_length = true;
+		bool use_tip_node = false;
+		NodePath tip_node = NodePath();
+		ObjectID tip_node_cache;
+
+		bool use_target_basis = false;
+		real_t roll = 0;
+	};
+
+	LocalVector<FABRIK_Joint_Data> fabrik_data_chain;
+	NodePath target_node;
+	ObjectID target_node_cache;
+
+	real_t chain_tolerance = 0.01;
+	int chain_max_iterations = 10;
+	int chain_iterations = 0;
+
+	void update_target_cache();
+	void update_joint_tip_cache(int p_joint_idx);
+
+	int final_joint_idx = 0;
+	Transform3D target_global_pose = Transform3D();
+	Transform3D origin_global_pose = Transform3D();
+
+	void chain_backwards();
+	void chain_forwards();
+	void chain_apply();
+
+protected:
+	static void _bind_methods();
+	bool _get(const StringName &p_path, Variant &r_ret) const;
+	bool _set(const StringName &p_path, const Variant &p_value);
+	void _get_property_list(List<PropertyInfo> *p_list) const;
+
+public:
+	virtual void _execute(real_t p_delta) override;
+	virtual void _setup_modification(SkeletonModificationStack3D *p_stack) override;
+
+	void set_target_node(const NodePath &p_target_node);
+	NodePath get_target_node() const;
+
+	int get_fabrik_data_chain_length();
+	void set_fabrik_data_chain_length(int p_new_length);
+
+	real_t get_chain_tolerance();
+	void set_chain_tolerance(real_t p_tolerance);
+
+	int get_chain_max_iterations();
+	void set_chain_max_iterations(int p_iterations);
+
+	String get_fabrik_joint_bone_name(int p_joint_idx) const;
+	void set_fabrik_joint_bone_name(int p_joint_idx, String p_bone_name);
+	int get_fabrik_joint_bone_index(int p_joint_idx) const;
+	void set_fabrik_joint_bone_index(int p_joint_idx, int p_bone_idx);
+	real_t get_fabrik_joint_length(int p_joint_idx) const;
+	void set_fabrik_joint_length(int p_joint_idx, real_t p_bone_length);
+	Vector3 get_fabrik_joint_magnet(int p_joint_idx) const;
+	void set_fabrik_joint_magnet(int p_joint_idx, Vector3 p_magnet);
+	bool get_fabrik_joint_auto_calculate_length(int p_joint_idx) const;
+	void set_fabrik_joint_auto_calculate_length(int p_joint_idx, bool p_auto_calculate);
+	void fabrik_joint_auto_calculate_length(int p_joint_idx);
+	bool get_fabrik_joint_use_tip_node(int p_joint_idx) const;
+	void set_fabrik_joint_use_tip_node(int p_joint_idx, bool p_use_tip_node);
+	NodePath get_fabrik_joint_tip_node(int p_joint_idx) const;
+	void set_fabrik_joint_tip_node(int p_joint_idx, NodePath p_tip_node);
+	bool get_fabrik_joint_use_target_basis(int p_joint_idx) const;
+	void set_fabrik_joint_use_target_basis(int p_joint_idx, bool p_use_basis);
+	real_t get_fabrik_joint_roll(int p_joint_idx) const;
+	void set_fabrik_joint_roll(int p_joint_idx, real_t p_roll);
+
+	SkeletonModification3DFABRIK();
+	~SkeletonModification3DFABRIK();
+};
+
+#endif //SKELETONMODIFICATION3DFABRIK_H

scene/resources/skeleton_modification_3d_jiggle.cpp

@@ -0,0 +1,573 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_jiggle.cpp                                  */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "scene/resources/skeleton_modification_3d_jiggle.h"
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+bool SkeletonModification3DJiggle::_set(const StringName &p_path, const Variant &p_value) {
+	String path = p_path;
+
+	if (path.begins_with("joint_data/")) {
+		const int jiggle_size = jiggle_data_chain.size();
+		int which = path.get_slicec('/', 1).to_int();
+		String what = path.get_slicec('/', 2);
+		ERR_FAIL_INDEX_V(which, jiggle_size, false);
+
+		if (what == "bone_name") {
+			set_jiggle_joint_bone_name(which, p_value);
+		} else if (what == "bone_index") {
+			set_jiggle_joint_bone_index(which, p_value);
+		} else if (what == "override_defaults") {
+			set_jiggle_joint_override(which, p_value);
+		} else if (what == "stiffness") {
+			set_jiggle_joint_stiffness(which, p_value);
+		} else if (what == "mass") {
+			set_jiggle_joint_mass(which, p_value);
+		} else if (what == "damping") {
+			set_jiggle_joint_damping(which, p_value);
+		} else if (what == "use_gravity") {
+			set_jiggle_joint_use_gravity(which, p_value);
+		} else if (what == "gravity") {
+			set_jiggle_joint_gravity(which, p_value);
+		} else if (what == "roll") {
+			set_jiggle_joint_roll(which, Math::deg2rad(real_t(p_value)));
+		}
+		return true;
+	} else {
+		if (path == "use_colliders") {
+			set_use_colliders(p_value);
+		} else if (path == "collision_mask") {
+			set_collision_mask(p_value);
+		}
+		return true;
+	}
+	return true;
+}
+
+bool SkeletonModification3DJiggle::_get(const StringName &p_path, Variant &r_ret) const {
+	String path = p_path;
+
+	if (path.begins_with("joint_data/")) {
+		const int jiggle_size = jiggle_data_chain.size();
+		int which = path.get_slicec('/', 1).to_int();
+		String what = path.get_slicec('/', 2);
+		ERR_FAIL_INDEX_V(which, jiggle_size, false);
+
+		if (what == "bone_name") {
+			r_ret = get_jiggle_joint_bone_name(which);
+		} else if (what == "bone_index") {
+			r_ret = get_jiggle_joint_bone_index(which);
+		} else if (what == "override_defaults") {
+			r_ret = get_jiggle_joint_override(which);
+		} else if (what == "stiffness") {
+			r_ret = get_jiggle_joint_stiffness(which);
+		} else if (what == "mass") {
+			r_ret = get_jiggle_joint_mass(which);
+		} else if (what == "damping") {
+			r_ret = get_jiggle_joint_damping(which);
+		} else if (what == "use_gravity") {
+			r_ret = get_jiggle_joint_use_gravity(which);
+		} else if (what == "gravity") {
+			r_ret = get_jiggle_joint_gravity(which);
+		} else if (what == "roll") {
+			r_ret = Math::rad2deg(get_jiggle_joint_roll(which));
+		}
+		return true;
+	} else {
+		if (path == "use_colliders") {
+			r_ret = get_use_colliders();
+		} else if (path == "collision_mask") {
+			r_ret = get_collision_mask();
+		}
+		return true;
+	}
+	return true;
+}
+
+void SkeletonModification3DJiggle::_get_property_list(List<PropertyInfo> *p_list) const {
+	p_list->push_back(PropertyInfo(Variant::BOOL, "use_colliders", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+	if (use_colliders) {
+		p_list->push_back(PropertyInfo(Variant::INT, "collision_mask", PROPERTY_HINT_LAYERS_3D_PHYSICS, "", PROPERTY_USAGE_DEFAULT));
+	}
+
+	for (uint32_t i = 0; i < jiggle_data_chain.size(); i++) {
+		String base_string = "joint_data/" + itos(i) + "/";
+
+		p_list->push_back(PropertyInfo(Variant::STRING_NAME, base_string + "bone_name", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+		p_list->push_back(PropertyInfo(Variant::INT, base_string + "bone_index", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+		p_list->push_back(PropertyInfo(Variant::FLOAT, base_string + "roll", PROPERTY_HINT_RANGE, "-360,360,0.01", PROPERTY_USAGE_DEFAULT));
+		p_list->push_back(PropertyInfo(Variant::BOOL, base_string + "override_defaults", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+
+		if (jiggle_data_chain[i].override_defaults) {
+			p_list->push_back(PropertyInfo(Variant::FLOAT, base_string + "stiffness", PROPERTY_HINT_RANGE, "0, 1000, 0.01", PROPERTY_USAGE_DEFAULT));
+			p_list->push_back(PropertyInfo(Variant::FLOAT, base_string + "mass", PROPERTY_HINT_RANGE, "0, 1000, 0.01", PROPERTY_USAGE_DEFAULT));
+			p_list->push_back(PropertyInfo(Variant::FLOAT, base_string + "damping", PROPERTY_HINT_RANGE, "0, 1, 0.01", PROPERTY_USAGE_DEFAULT));
+			p_list->push_back(PropertyInfo(Variant::BOOL, base_string + "use_gravity", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+			if (jiggle_data_chain[i].use_gravity) {
+				p_list->push_back(PropertyInfo(Variant::VECTOR3, base_string + "gravity", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+			}
+		}
+	}
+}
+
+void SkeletonModification3DJiggle::_execute(real_t p_delta) {
+	ERR_FAIL_COND_MSG(!stack || !is_setup || stack->skeleton == nullptr,
+			"Modification is not setup and therefore cannot execute!");
+	if (!enabled) {
+		return;
+	}
+	if (target_node_cache.is_null()) {
+		_print_execution_error(true, "Target cache is out of date. Attempting to update...");
+		update_cache();
+		return;
+	}
+	Node3D *target = Object::cast_to<Node3D>(ObjectDB::get_instance(target_node_cache));
+	_print_execution_error(!target || !target->is_inside_tree(), "Target node is not in the scene tree. Cannot execute modification!");
+
+	for (uint32_t i = 0; i < jiggle_data_chain.size(); i++) {
+		_execute_jiggle_joint(i, target, p_delta);
+	}
+
+	execution_error_found = false;
+}
+
+void SkeletonModification3DJiggle::_execute_jiggle_joint(int p_joint_idx, Node3D *p_target, real_t p_delta) {
+	// Adopted from: https://wiki.unity3d.com/index.php/JiggleBone
+	// With modifications by TwistedTwigleg.
+
+	if (jiggle_data_chain[p_joint_idx].bone_idx <= -2) {
+		jiggle_data_chain[p_joint_idx].bone_idx = stack->skeleton->find_bone(jiggle_data_chain[p_joint_idx].bone_name);
+	}
+	if (_print_execution_error(
+				jiggle_data_chain[p_joint_idx].bone_idx < 0 || jiggle_data_chain[p_joint_idx].bone_idx > stack->skeleton->get_bone_count(),
+				"Jiggle joint " + itos(p_joint_idx) + " bone index is invald. Cannot execute modification!")) {
+		return;
+	}
+
+	Transform3D new_bone_trans = stack->skeleton->local_pose_to_global_pose(jiggle_data_chain[p_joint_idx].bone_idx, stack->skeleton->get_bone_local_pose_override(jiggle_data_chain[p_joint_idx].bone_idx));
+	Vector3 target_position = stack->skeleton->world_transform_to_global_pose(p_target->get_global_transform()).origin;
+
+	jiggle_data_chain[p_joint_idx].force = (target_position - jiggle_data_chain[p_joint_idx].dynamic_position) * jiggle_data_chain[p_joint_idx].stiffness * p_delta;
+
+	if (jiggle_data_chain[p_joint_idx].use_gravity) {
+		Vector3 gravity_to_apply = new_bone_trans.basis.inverse().xform(jiggle_data_chain[p_joint_idx].gravity);
+		jiggle_data_chain[p_joint_idx].force += gravity_to_apply * p_delta;
+	}
+
+	jiggle_data_chain[p_joint_idx].acceleration = jiggle_data_chain[p_joint_idx].force / jiggle_data_chain[p_joint_idx].mass;
+	jiggle_data_chain[p_joint_idx].velocity += jiggle_data_chain[p_joint_idx].acceleration * (1 - jiggle_data_chain[p_joint_idx].damping);
+
+	jiggle_data_chain[p_joint_idx].dynamic_position += jiggle_data_chain[p_joint_idx].velocity + jiggle_data_chain[p_joint_idx].force;
+	jiggle_data_chain[p_joint_idx].dynamic_position += new_bone_trans.origin - jiggle_data_chain[p_joint_idx].last_position;
+	jiggle_data_chain[p_joint_idx].last_position = new_bone_trans.origin;
+
+	// Collision detection/response
+	if (use_colliders) {
+		if (execution_mode == SkeletonModificationStack3D::EXECUTION_MODE::execution_mode_physics_process) {
+			Ref<World3D> world_3d = stack->skeleton->get_world_3d();
+			ERR_FAIL_COND(world_3d.is_null());
+			PhysicsDirectSpaceState3D *space_state = PhysicsServer3D::get_singleton()->space_get_direct_state(world_3d->get_space());
+			PhysicsDirectSpaceState3D::RayResult ray_result;
+
+			// Convert to world transforms, which is what the physics server needs
+			Transform3D new_bone_trans_world = stack->skeleton->global_pose_to_world_transform(new_bone_trans);
+			Transform3D dynamic_position_world = stack->skeleton->global_pose_to_world_transform(Transform3D(Basis(), jiggle_data_chain[p_joint_idx].dynamic_position));
+
+			bool ray_hit = space_state->intersect_ray(new_bone_trans_world.origin, dynamic_position_world.get_origin(),
+					ray_result, Set<RID>(), collision_mask);
+
+			if (ray_hit) {
+				jiggle_data_chain[p_joint_idx].dynamic_position = jiggle_data_chain[p_joint_idx].last_noncollision_position;
+				jiggle_data_chain[p_joint_idx].acceleration = Vector3(0, 0, 0);
+				jiggle_data_chain[p_joint_idx].velocity = Vector3(0, 0, 0);
+			} else {
+				jiggle_data_chain[p_joint_idx].last_noncollision_position = jiggle_data_chain[p_joint_idx].dynamic_position;
+			}
+
+		} else {
+			WARN_PRINT_ONCE("Jiggle modifier: You cannot detect colliders without the stack mode being set to _physics_process!");
+		}
+	}
+
+	// Get the forward direction that the basis is facing in right now.
+	stack->skeleton->update_bone_rest_forward_vector(jiggle_data_chain[p_joint_idx].bone_idx);
+	Vector3 forward_vector = stack->skeleton->get_bone_axis_forward_vector(jiggle_data_chain[p_joint_idx].bone_idx);
+
+	// Rotate the bone using the dynamic position!
+	new_bone_trans.basis.rotate_to_align(forward_vector, new_bone_trans.origin.direction_to(jiggle_data_chain[p_joint_idx].dynamic_position));
+
+	// Roll
+	new_bone_trans.basis.rotate_local(forward_vector, jiggle_data_chain[p_joint_idx].roll);
+
+	new_bone_trans = stack->skeleton->global_pose_to_local_pose(jiggle_data_chain[p_joint_idx].bone_idx, new_bone_trans);
+	stack->skeleton->set_bone_local_pose_override(jiggle_data_chain[p_joint_idx].bone_idx, new_bone_trans, stack->strength, true);
+	stack->skeleton->force_update_bone_children_transforms(jiggle_data_chain[p_joint_idx].bone_idx);
+}
+
+void SkeletonModification3DJiggle::_update_jiggle_joint_data() {
+	for (uint32_t i = 0; i < jiggle_data_chain.size(); i++) {
+		if (!jiggle_data_chain[i].override_defaults) {
+			set_jiggle_joint_stiffness(i, stiffness);
+			set_jiggle_joint_mass(i, mass);
+			set_jiggle_joint_damping(i, damping);
+			set_jiggle_joint_use_gravity(i, use_gravity);
+			set_jiggle_joint_gravity(i, gravity);
+		}
+	}
+}
+
+void SkeletonModification3DJiggle::_setup_modification(SkeletonModificationStack3D *p_stack) {
+	stack = p_stack;
+
+	if (stack) {
+		is_setup = true;
+		execution_error_found = false;
+
+		if (stack->skeleton) {
+			for (uint32_t i = 0; i < jiggle_data_chain.size(); i++) {
+				int bone_idx = jiggle_data_chain[i].bone_idx;
+				if (bone_idx > 0 && bone_idx < stack->skeleton->get_bone_count()) {
+					jiggle_data_chain[i].dynamic_position = stack->skeleton->local_pose_to_global_pose(bone_idx, stack->skeleton->get_bone_local_pose_override(bone_idx)).origin;
+				}
+			}
+		}
+
+		update_cache();
+	}
+}
+
+void SkeletonModification3DJiggle::update_cache() {
+	if (!is_setup || !stack) {
+		_print_execution_error(true, "Cannot update target cache: modification is not properly setup!");
+		return;
+	}
+
+	target_node_cache = ObjectID();
+	if (stack->skeleton) {
+		if (stack->skeleton->is_inside_tree()) {
+			if (stack->skeleton->has_node(target_node)) {
+				Node *node = stack->skeleton->get_node(target_node);
+				ERR_FAIL_COND_MSG(!node || stack->skeleton == node,
+						"Cannot update target cache: node is this modification's skeleton or cannot be found!");
+				ERR_FAIL_COND_MSG(!node->is_inside_tree(),
+						"Cannot update target cache: node is not in the scene tree!");
+				target_node_cache = node->get_instance_id();
+
+				execution_error_found = false;
+			}
+		}
+	}
+}
+
+void SkeletonModification3DJiggle::set_target_node(const NodePath &p_target_node) {
+	target_node = p_target_node;
+	update_cache();
+}
+
+NodePath SkeletonModification3DJiggle::get_target_node() const {
+	return target_node;
+}
+
+void SkeletonModification3DJiggle::set_stiffness(real_t p_stiffness) {
+	ERR_FAIL_COND_MSG(p_stiffness < 0, "Stiffness cannot be set to a negative value!");
+	stiffness = p_stiffness;
+	_update_jiggle_joint_data();
+}
+
+real_t SkeletonModification3DJiggle::get_stiffness() const {
+	return stiffness;
+}
+
+void SkeletonModification3DJiggle::set_mass(real_t p_mass) {
+	ERR_FAIL_COND_MSG(p_mass < 0, "Mass cannot be set to a negative value!");
+	mass = p_mass;
+	_update_jiggle_joint_data();
+}
+
+real_t SkeletonModification3DJiggle::get_mass() const {
+	return mass;
+}
+
+void SkeletonModification3DJiggle::set_damping(real_t p_damping) {
+	ERR_FAIL_COND_MSG(p_damping < 0, "Damping cannot be set to a negative value!");
+	ERR_FAIL_COND_MSG(p_damping > 1, "Damping cannot be more than one!");
+	damping = p_damping;
+	_update_jiggle_joint_data();
+}
+
+real_t SkeletonModification3DJiggle::get_damping() const {
+	return damping;
+}
+
+void SkeletonModification3DJiggle::set_use_gravity(bool p_use_gravity) {
+	use_gravity = p_use_gravity;
+	_update_jiggle_joint_data();
+}
+
+bool SkeletonModification3DJiggle::get_use_gravity() const {
+	return use_gravity;
+}
+
+void SkeletonModification3DJiggle::set_gravity(Vector3 p_gravity) {
+	gravity = p_gravity;
+	_update_jiggle_joint_data();
+}
+
+Vector3 SkeletonModification3DJiggle::get_gravity() const {
+	return gravity;
+}
+
+void SkeletonModification3DJiggle::set_use_colliders(bool p_use_collider) {
+	use_colliders = p_use_collider;
+	notify_property_list_changed();
+}
+
+bool SkeletonModification3DJiggle::get_use_colliders() const {
+	return use_colliders;
+}
+
+void SkeletonModification3DJiggle::set_collision_mask(int p_mask) {
+	collision_mask = p_mask;
+}
+
+int SkeletonModification3DJiggle::get_collision_mask() const {
+	return collision_mask;
+}
+
+// Jiggle joint data functions
+int SkeletonModification3DJiggle::get_jiggle_data_chain_length() {
+	return jiggle_data_chain.size();
+}
+
+void SkeletonModification3DJiggle::set_jiggle_data_chain_length(int p_length) {
+	ERR_FAIL_COND(p_length < 0);
+	jiggle_data_chain.resize(p_length);
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+void SkeletonModification3DJiggle::set_jiggle_joint_bone_name(int p_joint_idx, String p_name) {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+
+	jiggle_data_chain[p_joint_idx].bone_name = p_name;
+	if (stack && stack->skeleton) {
+		jiggle_data_chain[p_joint_idx].bone_idx = stack->skeleton->find_bone(p_name);
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+String SkeletonModification3DJiggle::get_jiggle_joint_bone_name(int p_joint_idx) const {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, "");
+	return jiggle_data_chain[p_joint_idx].bone_name;
+}
+
+int SkeletonModification3DJiggle::get_jiggle_joint_bone_index(int p_joint_idx) const {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, -1);
+	return jiggle_data_chain[p_joint_idx].bone_idx;
+}
+
+void SkeletonModification3DJiggle::set_jiggle_joint_bone_index(int p_joint_idx, int p_bone_idx) {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	ERR_FAIL_COND_MSG(p_bone_idx < 0, "Bone index is out of range: The index is too low!");
+	jiggle_data_chain[p_joint_idx].bone_idx = p_bone_idx;
+
+	if (stack) {
+		if (stack->skeleton) {
+			jiggle_data_chain[p_joint_idx].bone_name = stack->skeleton->get_bone_name(p_bone_idx);
+		}
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+void SkeletonModification3DJiggle::set_jiggle_joint_override(int p_joint_idx, bool p_override) {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	jiggle_data_chain[p_joint_idx].override_defaults = p_override;
+	_update_jiggle_joint_data();
+	notify_property_list_changed();
+}
+
+bool SkeletonModification3DJiggle::get_jiggle_joint_override(int p_joint_idx) const {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, false);
+	return jiggle_data_chain[p_joint_idx].override_defaults;
+}
+
+void SkeletonModification3DJiggle::set_jiggle_joint_stiffness(int p_joint_idx, real_t p_stiffness) {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_COND_MSG(p_stiffness < 0, "Stiffness cannot be set to a negative value!");
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	jiggle_data_chain[p_joint_idx].stiffness = p_stiffness;
+}
+
+real_t SkeletonModification3DJiggle::get_jiggle_joint_stiffness(int p_joint_idx) const {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, -1);
+	return jiggle_data_chain[p_joint_idx].stiffness;
+}
+
+void SkeletonModification3DJiggle::set_jiggle_joint_mass(int p_joint_idx, real_t p_mass) {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_COND_MSG(p_mass < 0, "Mass cannot be set to a negative value!");
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	jiggle_data_chain[p_joint_idx].mass = p_mass;
+}
+
+real_t SkeletonModification3DJiggle::get_jiggle_joint_mass(int p_joint_idx) const {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, -1);
+	return jiggle_data_chain[p_joint_idx].mass;
+}
+
+void SkeletonModification3DJiggle::set_jiggle_joint_damping(int p_joint_idx, real_t p_damping) {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_COND_MSG(p_damping < 0, "Damping cannot be set to a negative value!");
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	jiggle_data_chain[p_joint_idx].damping = p_damping;
+}
+
+real_t SkeletonModification3DJiggle::get_jiggle_joint_damping(int p_joint_idx) const {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, -1);
+	return jiggle_data_chain[p_joint_idx].damping;
+}
+
+void SkeletonModification3DJiggle::set_jiggle_joint_use_gravity(int p_joint_idx, bool p_use_gravity) {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	jiggle_data_chain[p_joint_idx].use_gravity = p_use_gravity;
+	notify_property_list_changed();
+}
+
+bool SkeletonModification3DJiggle::get_jiggle_joint_use_gravity(int p_joint_idx) const {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, false);
+	return jiggle_data_chain[p_joint_idx].use_gravity;
+}
+
+void SkeletonModification3DJiggle::set_jiggle_joint_gravity(int p_joint_idx, Vector3 p_gravity) {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	jiggle_data_chain[p_joint_idx].gravity = p_gravity;
+}
+
+Vector3 SkeletonModification3DJiggle::get_jiggle_joint_gravity(int p_joint_idx) const {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, Vector3(0, 0, 0));
+	return jiggle_data_chain[p_joint_idx].gravity;
+}
+
+void SkeletonModification3DJiggle::set_jiggle_joint_roll(int p_joint_idx, real_t p_roll) {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX(p_joint_idx, bone_chain_size);
+	jiggle_data_chain[p_joint_idx].roll = p_roll;
+}
+
+real_t SkeletonModification3DJiggle::get_jiggle_joint_roll(int p_joint_idx) const {
+	const int bone_chain_size = jiggle_data_chain.size();
+	ERR_FAIL_INDEX_V(p_joint_idx, bone_chain_size, 0.0);
+	return jiggle_data_chain[p_joint_idx].roll;
+}
+
+void SkeletonModification3DJiggle::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("set_target_node", "target_nodepath"), &SkeletonModification3DJiggle::set_target_node);
+	ClassDB::bind_method(D_METHOD("get_target_node"), &SkeletonModification3DJiggle::get_target_node);
+
+	ClassDB::bind_method(D_METHOD("set_jiggle_data_chain_length", "length"), &SkeletonModification3DJiggle::set_jiggle_data_chain_length);
+	ClassDB::bind_method(D_METHOD("get_jiggle_data_chain_length"), &SkeletonModification3DJiggle::get_jiggle_data_chain_length);
+
+	ClassDB::bind_method(D_METHOD("set_stiffness", "stiffness"), &SkeletonModification3DJiggle::set_stiffness);
+	ClassDB::bind_method(D_METHOD("get_stiffness"), &SkeletonModification3DJiggle::get_stiffness);
+	ClassDB::bind_method(D_METHOD("set_mass", "mass"), &SkeletonModification3DJiggle::set_mass);
+	ClassDB::bind_method(D_METHOD("get_mass"), &SkeletonModification3DJiggle::get_mass);
+	ClassDB::bind_method(D_METHOD("set_damping", "damping"), &SkeletonModification3DJiggle::set_damping);
+	ClassDB::bind_method(D_METHOD("get_damping"), &SkeletonModification3DJiggle::get_damping);
+	ClassDB::bind_method(D_METHOD("set_use_gravity", "use_gravity"), &SkeletonModification3DJiggle::set_use_gravity);
+	ClassDB::bind_method(D_METHOD("get_use_gravity"), &SkeletonModification3DJiggle::get_use_gravity);
+	ClassDB::bind_method(D_METHOD("set_gravity", "gravity"), &SkeletonModification3DJiggle::set_gravity);
+	ClassDB::bind_method(D_METHOD("get_gravity"), &SkeletonModification3DJiggle::get_gravity);
+
+	ClassDB::bind_method(D_METHOD("set_use_colliders", "use_colliders"), &SkeletonModification3DJiggle::set_use_colliders);
+	ClassDB::bind_method(D_METHOD("get_use_colliders"), &SkeletonModification3DJiggle::get_use_colliders);
+	ClassDB::bind_method(D_METHOD("set_collision_mask", "mask"), &SkeletonModification3DJiggle::set_collision_mask);
+	ClassDB::bind_method(D_METHOD("get_collision_mask"), &SkeletonModification3DJiggle::get_collision_mask);
+
+	// Jiggle joint data functions
+	ClassDB::bind_method(D_METHOD("set_jiggle_joint_bone_name", "joint_idx", "name"), &SkeletonModification3DJiggle::set_jiggle_joint_bone_name);
+	ClassDB::bind_method(D_METHOD("get_jiggle_joint_bone_name", "joint_idx"), &SkeletonModification3DJiggle::get_jiggle_joint_bone_name);
+	ClassDB::bind_method(D_METHOD("set_jiggle_joint_bone_index", "joint_idx", "bone_idx"), &SkeletonModification3DJiggle::set_jiggle_joint_bone_index);
+	ClassDB::bind_method(D_METHOD("get_jiggle_joint_bone_index", "joint_idx"), &SkeletonModification3DJiggle::get_jiggle_joint_bone_index);
+	ClassDB::bind_method(D_METHOD("set_jiggle_joint_override", "joint_idx", "override"), &SkeletonModification3DJiggle::set_jiggle_joint_override);
+	ClassDB::bind_method(D_METHOD("get_jiggle_joint_override", "joint_idx"), &SkeletonModification3DJiggle::get_jiggle_joint_override);
+	ClassDB::bind_method(D_METHOD("set_jiggle_joint_stiffness", "joint_idx", "stiffness"), &SkeletonModification3DJiggle::set_jiggle_joint_stiffness);
+	ClassDB::bind_method(D_METHOD("get_jiggle_joint_stiffness", "joint_idx"), &SkeletonModification3DJiggle::get_jiggle_joint_stiffness);
+	ClassDB::bind_method(D_METHOD("set_jiggle_joint_mass", "joint_idx", "mass"), &SkeletonModification3DJiggle::set_jiggle_joint_mass);
+	ClassDB::bind_method(D_METHOD("get_jiggle_joint_mass", "joint_idx"), &SkeletonModification3DJiggle::get_jiggle_joint_mass);
+	ClassDB::bind_method(D_METHOD("set_jiggle_joint_damping", "joint_idx", "damping"), &SkeletonModification3DJiggle::set_jiggle_joint_damping);
+	ClassDB::bind_method(D_METHOD("get_jiggle_joint_damping", "joint_idx"), &SkeletonModification3DJiggle::get_jiggle_joint_damping);
+	ClassDB::bind_method(D_METHOD("set_jiggle_joint_use_gravity", "joint_idx", "use_gravity"), &SkeletonModification3DJiggle::set_jiggle_joint_use_gravity);
+	ClassDB::bind_method(D_METHOD("get_jiggle_joint_use_gravity", "joint_idx"), &SkeletonModification3DJiggle::get_jiggle_joint_use_gravity);
+	ClassDB::bind_method(D_METHOD("set_jiggle_joint_gravity", "joint_idx", "gravity"), &SkeletonModification3DJiggle::set_jiggle_joint_gravity);
+	ClassDB::bind_method(D_METHOD("get_jiggle_joint_gravity", "joint_idx"), &SkeletonModification3DJiggle::get_jiggle_joint_gravity);
+	ClassDB::bind_method(D_METHOD("set_jiggle_joint_roll", "joint_idx", "roll"), &SkeletonModification3DJiggle::set_jiggle_joint_roll);
+	ClassDB::bind_method(D_METHOD("get_jiggle_joint_roll", "joint_idx"), &SkeletonModification3DJiggle::get_jiggle_joint_roll);
+
+	ADD_PROPERTY(PropertyInfo(Variant::NODE_PATH, "target_nodepath", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "Node3D"), "set_target_node", "get_target_node");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "jiggle_data_chain_length", PROPERTY_HINT_RANGE, "0,100,1"), "set_jiggle_data_chain_length", "get_jiggle_data_chain_length");
+	ADD_GROUP("Default Joint Settings", "");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "stiffness"), "set_stiffness", "get_stiffness");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "mass"), "set_mass", "get_mass");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "damping", PROPERTY_HINT_RANGE, "0, 1, 0.01"), "set_damping", "get_damping");
+	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "use_gravity"), "set_use_gravity", "get_use_gravity");
+	ADD_PROPERTY(PropertyInfo(Variant::VECTOR3, "gravity"), "set_gravity", "get_gravity");
+	ADD_GROUP("", "");
+}
+
+SkeletonModification3DJiggle::SkeletonModification3DJiggle() {
+	stack = nullptr;
+	is_setup = false;
+	jiggle_data_chain = Vector<Jiggle_Joint_Data>();
+	stiffness = 3;
+	mass = 0.75;
+	damping = 0.75;
+	use_gravity = false;
+	gravity = Vector3(0, -6.0, 0);
+	enabled = true;
+}
+
+SkeletonModification3DJiggle::~SkeletonModification3DJiggle() {
+}

scene/resources/skeleton_modification_3d_jiggle.h

@@ -0,0 +1,138 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_jiggle.h                                    */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "core/templates/local_vector.h"
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+#ifndef SKELETONMODIFICATION3DJIGGLE_H
+#define SKELETONMODIFICATION3DJIGGLE_H
+
+class SkeletonModification3DJiggle : public SkeletonModification3D {
+	GDCLASS(SkeletonModification3DJiggle, SkeletonModification3D);
+
+private:
+	struct Jiggle_Joint_Data {
+		String bone_name = "";
+		int bone_idx = -1;
+
+		bool override_defaults = false;
+		real_t stiffness = 3;
+		real_t mass = 0.75;
+		real_t damping = 0.75;
+		bool use_gravity = false;
+		Vector3 gravity = Vector3(0, -6.0, 0);
+		real_t roll = 0;
+
+		Vector3 cached_rotation = Vector3(0, 0, 0);
+		Vector3 force = Vector3(0, 0, 0);
+		Vector3 acceleration = Vector3(0, 0, 0);
+		Vector3 velocity = Vector3(0, 0, 0);
+		Vector3 last_position = Vector3(0, 0, 0);
+		Vector3 dynamic_position = Vector3(0, 0, 0);
+
+		Vector3 last_noncollision_position = Vector3(0, 0, 0);
+	};
+
+	NodePath target_node;
+	ObjectID target_node_cache;
+	LocalVector<Jiggle_Joint_Data> jiggle_data_chain;
+
+	real_t stiffness = 3;
+	real_t mass = 0.75;
+	real_t damping = 0.75;
+	bool use_gravity = false;
+	Vector3 gravity = Vector3(0, -6.0, 0);
+
+	bool use_colliders = false;
+	uint32_t collision_mask = 1;
+
+	void update_cache();
+	void _execute_jiggle_joint(int p_joint_idx, Node3D *p_target, real_t p_delta);
+	void _update_jiggle_joint_data();
+
+protected:
+	static void _bind_methods();
+	bool _get(const StringName &p_path, Variant &r_ret) const;
+	bool _set(const StringName &p_path, const Variant &p_value);
+	void _get_property_list(List<PropertyInfo> *p_list) const;
+
+public:
+	virtual void _execute(real_t p_delta) override;
+	virtual void _setup_modification(SkeletonModificationStack3D *p_stack) override;
+
+	void set_target_node(const NodePath &p_target_node);
+	NodePath get_target_node() const;
+
+	void set_stiffness(real_t p_stiffness);
+	real_t get_stiffness() const;
+	void set_mass(real_t p_mass);
+	real_t get_mass() const;
+	void set_damping(real_t p_damping);
+	real_t get_damping() const;
+
+	void set_use_gravity(bool p_use_gravity);
+	bool get_use_gravity() const;
+	void set_gravity(Vector3 p_gravity);
+	Vector3 get_gravity() const;
+
+	void set_use_colliders(bool p_use_colliders);
+	bool get_use_colliders() const;
+	void set_collision_mask(int p_mask);
+	int get_collision_mask() const;
+
+	int get_jiggle_data_chain_length();
+	void set_jiggle_data_chain_length(int p_new_length);
+
+	void set_jiggle_joint_bone_name(int p_joint_idx, String p_name);
+	String get_jiggle_joint_bone_name(int p_joint_idx) const;
+	void set_jiggle_joint_bone_index(int p_joint_idx, int p_idx);
+	int get_jiggle_joint_bone_index(int p_joint_idx) const;
+
+	void set_jiggle_joint_override(int p_joint_idx, bool p_override);
+	bool get_jiggle_joint_override(int p_joint_idx) const;
+	void set_jiggle_joint_stiffness(int p_joint_idx, real_t p_stiffness);
+	real_t get_jiggle_joint_stiffness(int p_joint_idx) const;
+	void set_jiggle_joint_mass(int p_joint_idx, real_t p_mass);
+	real_t get_jiggle_joint_mass(int p_joint_idx) const;
+	void set_jiggle_joint_damping(int p_joint_idx, real_t p_damping);
+	real_t get_jiggle_joint_damping(int p_joint_idx) const;
+	void set_jiggle_joint_use_gravity(int p_joint_idx, bool p_use_gravity);
+	bool get_jiggle_joint_use_gravity(int p_joint_idx) const;
+	void set_jiggle_joint_gravity(int p_joint_idx, Vector3 p_gravity);
+	Vector3 get_jiggle_joint_gravity(int p_joint_idx) const;
+	void set_jiggle_joint_roll(int p_joint_idx, real_t p_roll);
+	real_t get_jiggle_joint_roll(int p_joint_idx) const;
+
+	SkeletonModification3DJiggle();
+	~SkeletonModification3DJiggle();
+};
+
+#endif //SKELETONMODIFICATION3DJIGGLE_H

scene/resources/skeleton_modification_3d_lookat.cpp

@@ -0,0 +1,265 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_lookat.cpp                                  */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "scene/resources/skeleton_modification_3d_lookat.h"
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+bool SkeletonModification3DLookAt::_set(const StringName &p_path, const Variant &p_value) {
+	if (p_path == "lock_rotation_to_plane") {
+		set_lock_rotation_to_plane(p_value);
+	} else if (p_path == "lock_rotation_plane") {
+		set_lock_rotation_plane(p_value);
+	} else if (p_path == "additional_rotation") {
+		Vector3 tmp = p_value;
+		tmp.x = Math::deg2rad(tmp.x);
+		tmp.y = Math::deg2rad(tmp.y);
+		tmp.z = Math::deg2rad(tmp.z);
+		set_additional_rotation(tmp);
+	}
+
+	return true;
+}
+
+bool SkeletonModification3DLookAt::_get(const StringName &p_path, Variant &r_ret) const {
+	if (p_path == "lock_rotation_to_plane") {
+		r_ret = get_lock_rotation_to_plane();
+	} else if (p_path == "lock_rotation_plane") {
+		r_ret = get_lock_rotation_plane();
+	} else if (p_path == "additional_rotation") {
+		Vector3 tmp = get_additional_rotation();
+		tmp.x = Math::rad2deg(tmp.x);
+		tmp.y = Math::rad2deg(tmp.y);
+		tmp.z = Math::rad2deg(tmp.z);
+		r_ret = tmp;
+	}
+
+	return true;
+}
+
+void SkeletonModification3DLookAt::_get_property_list(List<PropertyInfo> *p_list) const {
+	p_list->push_back(PropertyInfo(Variant::BOOL, "lock_rotation_to_plane", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+	if (lock_rotation_to_plane) {
+		p_list->push_back(PropertyInfo(Variant::INT, "lock_rotation_plane", PROPERTY_HINT_ENUM, "X plane, Y plane, Z plane", PROPERTY_USAGE_DEFAULT));
+	}
+	p_list->push_back(PropertyInfo(Variant::VECTOR3, "additional_rotation", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+}
+
+void SkeletonModification3DLookAt::_execute(real_t p_delta) {
+	ERR_FAIL_COND_MSG(!stack || !is_setup || stack->skeleton == nullptr,
+			"Modification is not setup and therefore cannot execute!");
+	if (!enabled) {
+		return;
+	}
+
+	if (target_node_cache.is_null()) {
+		_print_execution_error(true, "Target cache is out of date. Attempting to update...");
+		update_cache();
+		return;
+	}
+
+	if (bone_idx <= -2) {
+		bone_idx = stack->skeleton->find_bone(bone_name);
+	}
+
+	Node3D *target = Object::cast_to<Node3D>(ObjectDB::get_instance(target_node_cache));
+	if (_print_execution_error(!target || !target->is_inside_tree(), "Target node is not in the scene tree. Cannot execute modification!")) {
+		return;
+	}
+	if (_print_execution_error(bone_idx <= -1, "Bone index is invalid. Cannot execute modification!")) {
+		return;
+	}
+
+	Transform3D new_bone_trans = stack->skeleton->get_bone_local_pose_override(bone_idx);
+	Vector3 target_pos = stack->skeleton->global_pose_to_local_pose(bone_idx, stack->skeleton->world_transform_to_global_pose(target->get_global_transform())).origin;
+
+	// Lock the rotation to a plane relative to the bone by changing the target position
+	if (lock_rotation_to_plane) {
+		if (lock_rotation_plane == ROTATION_PLANE::ROTATION_PLANE_X) {
+			target_pos.x = new_bone_trans.origin.x;
+		} else if (lock_rotation_plane == ROTATION_PLANE::ROTATION_PLANE_Y) {
+			target_pos.y = new_bone_trans.origin.y;
+		} else if (lock_rotation_plane == ROTATION_PLANE::ROTATION_PLANE_Z) {
+			target_pos.z = new_bone_trans.origin.z;
+		}
+	}
+
+	// Look at the target!
+	new_bone_trans = new_bone_trans.looking_at(target_pos, Vector3(0, 1, 0));
+	// Convert from Z-forward to whatever direction the bone faces.
+	stack->skeleton->update_bone_rest_forward_vector(bone_idx);
+	new_bone_trans.basis = stack->skeleton->global_pose_z_forward_to_bone_forward(bone_idx, new_bone_trans.basis);
+
+	// Apply additional rotation
+	new_bone_trans.basis.rotate_local(Vector3(1, 0, 0), additional_rotation.x);
+	new_bone_trans.basis.rotate_local(Vector3(0, 1, 0), additional_rotation.y);
+	new_bone_trans.basis.rotate_local(Vector3(0, 0, 1), additional_rotation.z);
+
+	stack->skeleton->set_bone_local_pose_override(bone_idx, new_bone_trans, stack->strength, true);
+	stack->skeleton->force_update_bone_children_transforms(bone_idx);
+
+	// If we completed it successfully, then we can set execution_error_found to false
+	execution_error_found = false;
+}
+
+void SkeletonModification3DLookAt::_setup_modification(SkeletonModificationStack3D *p_stack) {
+	stack = p_stack;
+
+	if (stack != nullptr) {
+		is_setup = true;
+		execution_error_found = false;
+		update_cache();
+	}
+}
+
+void SkeletonModification3DLookAt::set_bone_name(String p_name) {
+	bone_name = p_name;
+	if (stack) {
+		if (stack->skeleton) {
+			bone_idx = stack->skeleton->find_bone(bone_name);
+		}
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+String SkeletonModification3DLookAt::get_bone_name() const {
+	return bone_name;
+}
+
+int SkeletonModification3DLookAt::get_bone_index() const {
+	return bone_idx;
+}
+
+void SkeletonModification3DLookAt::set_bone_index(int p_bone_idx) {
+	ERR_FAIL_COND_MSG(p_bone_idx < 0, "Bone index is out of range: The index is too low!");
+	bone_idx = p_bone_idx;
+
+	if (stack) {
+		if (stack->skeleton) {
+			bone_name = stack->skeleton->get_bone_name(p_bone_idx);
+		}
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+void SkeletonModification3DLookAt::update_cache() {
+	if (!is_setup || !stack) {
+		_print_execution_error(true, "Cannot update target cache: modification is not properly setup!");
+		return;
+	}
+
+	target_node_cache = ObjectID();
+	if (stack->skeleton) {
+		if (stack->skeleton->is_inside_tree()) {
+			if (stack->skeleton->has_node(target_node)) {
+				Node *node = stack->skeleton->get_node(target_node);
+				ERR_FAIL_COND_MSG(!node || stack->skeleton == node,
+						"Cannot update target cache: Node is this modification's skeleton or cannot be found!");
+				ERR_FAIL_COND_MSG(!node->is_inside_tree(),
+						"Cannot update target cache: Node is not in the scene tree!");
+				target_node_cache = node->get_instance_id();
+
+				execution_error_found = false;
+			}
+		}
+	}
+}
+
+void SkeletonModification3DLookAt::set_target_node(const NodePath &p_target_node) {
+	target_node = p_target_node;
+	update_cache();
+}
+
+NodePath SkeletonModification3DLookAt::get_target_node() const {
+	return target_node;
+}
+
+Vector3 SkeletonModification3DLookAt::get_additional_rotation() const {
+	return additional_rotation;
+}
+
+void SkeletonModification3DLookAt::set_additional_rotation(Vector3 p_offset) {
+	additional_rotation = p_offset;
+}
+
+bool SkeletonModification3DLookAt::get_lock_rotation_to_plane() const {
+	return lock_rotation_plane;
+}
+
+void SkeletonModification3DLookAt::set_lock_rotation_to_plane(bool p_lock_rotation) {
+	lock_rotation_to_plane = p_lock_rotation;
+	notify_property_list_changed();
+}
+
+int SkeletonModification3DLookAt::get_lock_rotation_plane() const {
+	return lock_rotation_plane;
+}
+
+void SkeletonModification3DLookAt::set_lock_rotation_plane(int p_plane) {
+	lock_rotation_plane = p_plane;
+}
+
+void SkeletonModification3DLookAt::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("set_bone_name", "name"), &SkeletonModification3DLookAt::set_bone_name);
+	ClassDB::bind_method(D_METHOD("get_bone_name"), &SkeletonModification3DLookAt::get_bone_name);
+
+	ClassDB::bind_method(D_METHOD("set_bone_index", "bone_idx"), &SkeletonModification3DLookAt::set_bone_index);
+	ClassDB::bind_method(D_METHOD("get_bone_index"), &SkeletonModification3DLookAt::get_bone_index);
+
+	ClassDB::bind_method(D_METHOD("set_target_node", "target_nodepath"), &SkeletonModification3DLookAt::set_target_node);
+	ClassDB::bind_method(D_METHOD("get_target_node"), &SkeletonModification3DLookAt::get_target_node);
+
+	ClassDB::bind_method(D_METHOD("set_additional_rotation", "additional_rotation"), &SkeletonModification3DLookAt::set_additional_rotation);
+	ClassDB::bind_method(D_METHOD("get_additional_rotation"), &SkeletonModification3DLookAt::get_additional_rotation);
+
+	ClassDB::bind_method(D_METHOD("set_lock_rotation_to_plane", "lock_to_plane"), &SkeletonModification3DLookAt::set_lock_rotation_to_plane);
+	ClassDB::bind_method(D_METHOD("get_lock_rotation_to_plane"), &SkeletonModification3DLookAt::get_lock_rotation_to_plane);
+	ClassDB::bind_method(D_METHOD("set_lock_rotation_plane", "plane"), &SkeletonModification3DLookAt::set_lock_rotation_plane);
+	ClassDB::bind_method(D_METHOD("get_lock_rotation_plane"), &SkeletonModification3DLookAt::get_lock_rotation_plane);
+
+	ADD_PROPERTY(PropertyInfo(Variant::STRING_NAME, "bone_name"), "set_bone_name", "get_bone_name");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "bone_index"), "set_bone_index", "get_bone_index");
+	ADD_PROPERTY(PropertyInfo(Variant::NODE_PATH, "target_nodepath", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "Node3D"), "set_target_node", "get_target_node");
+}
+
+SkeletonModification3DLookAt::SkeletonModification3DLookAt() {
+	stack = nullptr;
+	is_setup = false;
+	bone_name = "";
+	bone_idx = -2;
+	additional_rotation = Vector3();
+	lock_rotation_to_plane = false;
+	enabled = true;
+}
+
+SkeletonModification3DLookAt::~SkeletonModification3DLookAt() {
+}

scene/resources/skeleton_modification_3d_lookat.h

@@ -0,0 +1,89 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_lookat.h                                    */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+#ifndef SKELETONMODIFICATION3DLOOKAT_H
+#define SKELETONMODIFICATION3DLOOKAT_H
+
+class SkeletonModification3DLookAt : public SkeletonModification3D {
+	GDCLASS(SkeletonModification3DLookAt, SkeletonModification3D);
+
+private:
+	String bone_name = "";
+	int bone_idx = -1;
+	NodePath target_node;
+	ObjectID target_node_cache;
+
+	Vector3 additional_rotation = Vector3(1, 0, 0);
+	bool lock_rotation_to_plane = false;
+	int lock_rotation_plane = ROTATION_PLANE_X;
+
+	void update_cache();
+
+protected:
+	static void _bind_methods();
+	bool _get(const StringName &p_path, Variant &r_ret) const;
+	bool _set(const StringName &p_path, const Variant &p_value);
+	void _get_property_list(List<PropertyInfo> *p_list) const;
+
+public:
+	enum ROTATION_PLANE {
+		ROTATION_PLANE_X,
+		ROTATION_PLANE_Y,
+		ROTATION_PLANE_Z
+	};
+
+	virtual void _execute(real_t p_delta) override;
+	virtual void _setup_modification(SkeletonModificationStack3D *p_stack) override;
+
+	void set_bone_name(String p_name);
+	String get_bone_name() const;
+
+	void set_bone_index(int p_idx);
+	int get_bone_index() const;
+
+	void set_target_node(const NodePath &p_target_node);
+	NodePath get_target_node() const;
+
+	void set_additional_rotation(Vector3 p_offset);
+	Vector3 get_additional_rotation() const;
+
+	void set_lock_rotation_to_plane(bool p_lock_to_plane);
+	bool get_lock_rotation_to_plane() const;
+	void set_lock_rotation_plane(int p_plane);
+	int get_lock_rotation_plane() const;
+
+	SkeletonModification3DLookAt();
+	~SkeletonModification3DLookAt();
+};
+
+#endif //SKELETONMODIFICATION3DLOOKAT_H

scene/resources/skeleton_modification_3d_stackholder.cpp

@@ -0,0 +1,104 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_stackholder.cpp                             */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "scene/resources/skeleton_modification_3d_stackholder.h"
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+bool SkeletonModification3DStackHolder::_set(const StringName &p_path, const Variant &p_value) {
+	String path = p_path;
+
+	if (path == "held_modification_stack") {
+		set_held_modification_stack(p_value);
+	}
+	return true;
+}
+
+bool SkeletonModification3DStackHolder::_get(const StringName &p_path, Variant &r_ret) const {
+	String path = p_path;
+
+	if (path == "held_modification_stack") {
+		r_ret = get_held_modification_stack();
+	}
+	return true;
+}
+
+void SkeletonModification3DStackHolder::_get_property_list(List<PropertyInfo> *p_list) const {
+	p_list->push_back(PropertyInfo(Variant::OBJECT, "held_modification_stack", PROPERTY_HINT_RESOURCE_TYPE, "SkeletonModificationStack3D", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_DO_NOT_SHARE_ON_DUPLICATE));
+}
+
+void SkeletonModification3DStackHolder::_execute(real_t p_delta) {
+	ERR_FAIL_COND_MSG(!stack || !is_setup || stack->skeleton == nullptr,
+			"Modification is not setup and therefore cannot execute!");
+
+	if (held_modification_stack.is_valid()) {
+		held_modification_stack->execute(p_delta, execution_mode);
+	}
+}
+
+void SkeletonModification3DStackHolder::_setup_modification(SkeletonModificationStack3D *p_stack) {
+	stack = p_stack;
+
+	if (stack != nullptr) {
+		is_setup = true;
+
+		if (held_modification_stack.is_valid()) {
+			held_modification_stack->set_skeleton(stack->get_skeleton());
+			held_modification_stack->setup();
+		}
+	}
+}
+
+void SkeletonModification3DStackHolder::set_held_modification_stack(Ref<SkeletonModificationStack3D> p_held_stack) {
+	held_modification_stack = p_held_stack;
+
+	if (is_setup && held_modification_stack.is_valid()) {
+		held_modification_stack->set_skeleton(stack->get_skeleton());
+		held_modification_stack->setup();
+	}
+}
+
+Ref<SkeletonModificationStack3D> SkeletonModification3DStackHolder::get_held_modification_stack() const {
+	return held_modification_stack;
+}
+
+void SkeletonModification3DStackHolder::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("set_held_modification_stack", "held_modification_stack"), &SkeletonModification3DStackHolder::set_held_modification_stack);
+	ClassDB::bind_method(D_METHOD("get_held_modification_stack"), &SkeletonModification3DStackHolder::get_held_modification_stack);
+}
+
+SkeletonModification3DStackHolder::SkeletonModification3DStackHolder() {
+	stack = nullptr;
+	is_setup = false;
+	enabled = true;
+}
+
+SkeletonModification3DStackHolder::~SkeletonModification3DStackHolder() {
+}

scene/resources/skeleton_modification_3d_stackholder.h

@@ -0,0 +1,59 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_stackholder.h                               */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+#ifndef SKELETONMODIFICATION3DSTACKHOLDER_H
+#define SKELETONMODIFICATION3DSTACKHOLDER_H
+
+class SkeletonModification3DStackHolder : public SkeletonModification3D {
+	GDCLASS(SkeletonModification3DStackHolder, SkeletonModification3D);
+
+protected:
+	static void _bind_methods();
+	bool _get(const StringName &p_path, Variant &r_ret) const;
+	bool _set(const StringName &p_path, const Variant &p_value);
+	void _get_property_list(List<PropertyInfo> *p_list) const;
+
+public:
+	Ref<SkeletonModificationStack3D> held_modification_stack;
+
+	virtual void _execute(real_t p_delta) override;
+	virtual void _setup_modification(SkeletonModificationStack3D *p_stack) override;
+
+	void set_held_modification_stack(Ref<SkeletonModificationStack3D> p_held_stack);
+	Ref<SkeletonModificationStack3D> get_held_modification_stack() const;
+
+	SkeletonModification3DStackHolder();
+	~SkeletonModification3DStackHolder();
+};
+
+#endif //SKELETONMODIFICATION3DSTACKHOLDER_H

scene/resources/skeleton_modification_3d_twoboneik.cpp

@@ -0,0 +1,599 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_twoboneik.cpp                               */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "scene/resources/skeleton_modification_3d_twoboneik.h"
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+bool SkeletonModification3DTwoBoneIK::_set(const StringName &p_path, const Variant &p_value) {
+	String path = p_path;
+
+	if (path == "use_tip_node") {
+		set_use_tip_node(p_value);
+	} else if (path == "tip_node") {
+		set_tip_node(p_value);
+	} else if (path == "auto_calculate_joint_length") {
+		set_auto_calculate_joint_length(p_value);
+	} else if (path == "use_pole_node") {
+		set_use_pole_node(p_value);
+	} else if (path == "pole_node") {
+		set_pole_node(p_value);
+	} else if (path == "joint_one_length") {
+		set_joint_one_length(p_value);
+	} else if (path == "joint_two_length") {
+		set_joint_two_length(p_value);
+	} else if (path == "joint_one/bone_name") {
+		set_joint_one_bone_name(p_value);
+	} else if (path == "joint_one/bone_idx") {
+		set_joint_one_bone_idx(p_value);
+	} else if (path == "joint_one/roll") {
+		set_joint_one_roll(Math::deg2rad(real_t(p_value)));
+	} else if (path == "joint_two/bone_name") {
+		set_joint_two_bone_name(p_value);
+	} else if (path == "joint_two/bone_idx") {
+		set_joint_two_bone_idx(p_value);
+	} else if (path == "joint_two/roll") {
+		set_joint_two_roll(Math::deg2rad(real_t(p_value)));
+	}
+
+	return true;
+}
+
+bool SkeletonModification3DTwoBoneIK::_get(const StringName &p_path, Variant &r_ret) const {
+	String path = p_path;
+
+	if (path == "use_tip_node") {
+		r_ret = get_use_tip_node();
+	} else if (path == "tip_node") {
+		r_ret = get_tip_node();
+	} else if (path == "auto_calculate_joint_length") {
+		r_ret = get_auto_calculate_joint_length();
+	} else if (path == "use_pole_node") {
+		r_ret = get_use_pole_node();
+	} else if (path == "pole_node") {
+		r_ret = get_pole_node();
+	} else if (path == "joint_one_length") {
+		r_ret = get_joint_one_length();
+	} else if (path == "joint_two_length") {
+		r_ret = get_joint_two_length();
+	} else if (path == "joint_one/bone_name") {
+		r_ret = get_joint_one_bone_name();
+	} else if (path == "joint_one/bone_idx") {
+		r_ret = get_joint_one_bone_idx();
+	} else if (path == "joint_one/roll") {
+		r_ret = Math::rad2deg(get_joint_one_roll());
+	} else if (path == "joint_two/bone_name") {
+		r_ret = get_joint_two_bone_name();
+	} else if (path == "joint_two/bone_idx") {
+		r_ret = get_joint_two_bone_idx();
+	} else if (path == "joint_two/roll") {
+		r_ret = Math::rad2deg(get_joint_two_roll());
+	}
+
+	return true;
+}
+
+void SkeletonModification3DTwoBoneIK::_get_property_list(List<PropertyInfo> *p_list) const {
+	p_list->push_back(PropertyInfo(Variant::BOOL, "use_tip_node", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+	if (use_tip_node) {
+		p_list->push_back(PropertyInfo(Variant::NODE_PATH, "tip_node", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "Node3D", PROPERTY_USAGE_DEFAULT));
+	}
+
+	p_list->push_back(PropertyInfo(Variant::BOOL, "auto_calculate_joint_length", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+	if (!auto_calculate_joint_length) {
+		p_list->push_back(PropertyInfo(Variant::FLOAT, "joint_one_length", PROPERTY_HINT_RANGE, "-1, 10000, 0.001", PROPERTY_USAGE_DEFAULT));
+		p_list->push_back(PropertyInfo(Variant::FLOAT, "joint_two_length", PROPERTY_HINT_RANGE, "-1, 10000, 0.001", PROPERTY_USAGE_DEFAULT));
+	}
+
+	p_list->push_back(PropertyInfo(Variant::BOOL, "use_pole_node", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+	if (use_pole_node) {
+		p_list->push_back(PropertyInfo(Variant::NODE_PATH, "pole_node", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "Node3D", PROPERTY_USAGE_DEFAULT));
+	}
+
+	p_list->push_back(PropertyInfo(Variant::STRING_NAME, "joint_one/bone_name", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+	p_list->push_back(PropertyInfo(Variant::INT, "joint_one/bone_idx", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+	p_list->push_back(PropertyInfo(Variant::FLOAT, "joint_one/roll", PROPERTY_HINT_RANGE, "-360, 360, 0.01", PROPERTY_USAGE_DEFAULT));
+
+	p_list->push_back(PropertyInfo(Variant::STRING_NAME, "joint_two/bone_name", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+	p_list->push_back(PropertyInfo(Variant::INT, "joint_two/bone_idx", PROPERTY_HINT_NONE, "", PROPERTY_USAGE_DEFAULT));
+	p_list->push_back(PropertyInfo(Variant::FLOAT, "joint_two/roll", PROPERTY_HINT_RANGE, "-360, 360, 0.01", PROPERTY_USAGE_DEFAULT));
+}
+
+void SkeletonModification3DTwoBoneIK::_execute(real_t p_delta) {
+	ERR_FAIL_COND_MSG(!stack || !is_setup || stack->skeleton == nullptr,
+			"Modification is not setup and therefore cannot execute!");
+
+	if (!enabled) {
+		return;
+	}
+
+	if (_print_execution_error(joint_one_bone_idx < 0 || joint_two_bone_idx < 0,
+				"One (or more) of the bones in the modification have invalid bone indexes. Cannot execute modification!")) {
+		return;
+	}
+
+	if (target_node_cache.is_null()) {
+		_print_execution_error(true, "Target cache is out of date. Attempting to update...");
+		update_cache_target();
+		return;
+	}
+
+	// Update joint lengths (if needed)
+	if (auto_calculate_joint_length && (joint_one_length < 0 || joint_two_length < 0)) {
+		calculate_joint_lengths();
+	}
+
+	// Adopted from the links below:
+	// http://theorangeduck.com/page/simple-two-joint
+	// https://www.alanzucconi.com/2018/05/02/ik-2d-2/
+	// With modifications by TwistedTwigleg
+	Node3D *target = Object::cast_to<Node3D>(ObjectDB::get_instance(target_node_cache));
+	if (_print_execution_error(!target || !target->is_inside_tree(), "Target node is not in the scene tree. Cannot execute modification!")) {
+		return;
+	}
+	Transform3D target_trans = stack->skeleton->world_transform_to_global_pose(target->get_global_transform());
+
+	Transform3D bone_one_trans;
+	Transform3D bone_two_trans;
+
+	// Make the first joint look at the pole, and the second look at the target. That way, the
+	// TwoBoneIK solver has to really only handle extension/contraction, which should make it align with the pole.
+	if (use_pole_node) {
+		if (pole_node_cache.is_null()) {
+			_print_execution_error(true, "Pole cache is out of date. Attempting to update...");
+			update_cache_pole();
+			return;
+		}
+
+		Node3D *pole = Object::cast_to<Node3D>(ObjectDB::get_instance(pole_node_cache));
+		if (_print_execution_error(!pole || !pole->is_inside_tree(), "Pole node is not in the scene tree. Cannot execute modification!")) {
+			return;
+		}
+		Transform3D pole_trans = stack->skeleton->world_transform_to_global_pose(pole->get_global_transform());
+
+		bone_one_trans = stack->skeleton->local_pose_to_global_pose(joint_one_bone_idx, stack->skeleton->get_bone_local_pose_override(joint_one_bone_idx));
+		bone_one_trans = bone_one_trans.looking_at(pole_trans.origin, Vector3(0, 1, 0));
+		bone_one_trans.basis = stack->skeleton->global_pose_z_forward_to_bone_forward(joint_one_bone_idx, bone_one_trans.basis);
+		stack->skeleton->update_bone_rest_forward_vector(joint_one_bone_idx);
+		bone_one_trans.basis.rotate_local(stack->skeleton->get_bone_axis_forward_vector(joint_one_bone_idx), joint_one_roll);
+		stack->skeleton->set_bone_local_pose_override(joint_one_bone_idx, stack->skeleton->global_pose_to_local_pose(joint_one_bone_idx, bone_one_trans), stack->strength, true);
+		stack->skeleton->force_update_bone_children_transforms(joint_one_bone_idx);
+
+		bone_two_trans = stack->skeleton->local_pose_to_global_pose(joint_two_bone_idx, stack->skeleton->get_bone_local_pose_override(joint_two_bone_idx));
+		bone_two_trans = bone_two_trans.looking_at(target_trans.origin, Vector3(0, 1, 0));
+		bone_two_trans.basis = stack->skeleton->global_pose_z_forward_to_bone_forward(joint_two_bone_idx, bone_two_trans.basis);
+		stack->skeleton->update_bone_rest_forward_vector(joint_two_bone_idx);
+		bone_two_trans.basis.rotate_local(stack->skeleton->get_bone_axis_forward_vector(joint_two_bone_idx), joint_two_roll);
+		stack->skeleton->set_bone_local_pose_override(joint_two_bone_idx, stack->skeleton->global_pose_to_local_pose(joint_two_bone_idx, bone_two_trans), stack->strength, true);
+		stack->skeleton->force_update_bone_children_transforms(joint_two_bone_idx);
+	} else {
+		bone_one_trans = stack->skeleton->local_pose_to_global_pose(joint_one_bone_idx, stack->skeleton->get_bone_local_pose_override(joint_one_bone_idx));
+		bone_two_trans = stack->skeleton->local_pose_to_global_pose(joint_two_bone_idx, stack->skeleton->get_bone_local_pose_override(joint_two_bone_idx));
+	}
+
+	Transform3D bone_two_tip_trans;
+	if (use_tip_node) {
+		if (tip_node_cache.is_null()) {
+			_print_execution_error(true, "Tip cache is out of date. Attempting to update...");
+			update_cache_tip();
+			return;
+		}
+		Node3D *tip = Object::cast_to<Node3D>(ObjectDB::get_instance(tip_node_cache));
+		if (_print_execution_error(!tip || !tip->is_inside_tree(), "Tip node is not in the scene tree. Cannot execute modification!")) {
+			return;
+		}
+		bone_two_tip_trans = stack->skeleton->world_transform_to_global_pose(tip->get_global_transform());
+	} else {
+		stack->skeleton->update_bone_rest_forward_vector(joint_two_bone_idx);
+		bone_two_tip_trans = bone_two_trans;
+		bone_two_tip_trans.origin += bone_two_trans.basis.xform(stack->skeleton->get_bone_axis_forward_vector(joint_two_bone_idx)).normalized() * joint_two_length;
+	}
+
+	real_t joint_one_to_target_length = bone_one_trans.origin.distance_to(target_trans.origin);
+	if (joint_one_length + joint_two_length < joint_one_to_target_length) {
+		// Set the target *just* out of reach to straighten the bones
+		joint_one_to_target_length = joint_one_length + joint_two_length + 0.01;
+	} else if (joint_one_to_target_length < joint_one_length) {
+		// Place the target in reach so the solver doesn't do crazy things
+		joint_one_to_target_length = joint_one_length;
+	}
+
+	// Get the square lengths for all three sides of the triangle we'll use to calculate the angles
+	real_t sqr_one_length = joint_one_length * joint_one_length;
+	real_t sqr_two_length = joint_two_length * joint_two_length;
+	real_t sqr_three_length = joint_one_to_target_length * joint_one_to_target_length;
+
+	// Calculate the angles for the first joint using the law of cosigns
+	real_t ac_ab_0 = Math::acos(CLAMP(bone_two_tip_trans.origin.direction_to(bone_one_trans.origin).dot(bone_two_trans.origin.direction_to(bone_one_trans.origin)), -1, 1));
+	real_t ac_at_0 = Math::acos(CLAMP(bone_one_trans.origin.direction_to(bone_two_tip_trans.origin).dot(bone_one_trans.origin.direction_to(target_trans.origin)), -1, 1));
+	real_t ac_ab_1 = Math::acos(CLAMP((sqr_two_length - sqr_one_length - sqr_three_length) / (-2.0 * joint_one_length * joint_one_to_target_length), -1, 1));
+
+	// Calculate the angles of rotation. Angle 0 is the extension/contraction axis, while angle 1 is the rotation axis to align the triangle to the target
+	Vector3 axis_0 = bone_one_trans.origin.direction_to(bone_two_tip_trans.origin).cross(bone_one_trans.origin.direction_to(bone_two_trans.origin));
+	Vector3 axis_1 = bone_one_trans.origin.direction_to(bone_two_tip_trans.origin).cross(bone_one_trans.origin.direction_to(target_trans.origin));
+
+	// Make a quaternion with the delta rotation needed to rotate the first joint into alignment and apply it to the transform.
+	Quaternion bone_one_quat = bone_one_trans.basis.get_rotation_quaternion();
+	Quaternion rot_0 = Quaternion(bone_one_quat.inverse().xform(axis_0).normalized(), (ac_ab_1 - ac_ab_0));
+	Quaternion rot_2 = Quaternion(bone_one_quat.inverse().xform(axis_1).normalized(), ac_at_0);
+	bone_one_trans.basis.set_quaternion(bone_one_quat * (rot_0 * rot_2));
+
+	stack->skeleton->update_bone_rest_forward_vector(joint_one_bone_idx);
+	bone_one_trans.basis.rotate_local(stack->skeleton->get_bone_axis_forward_vector(joint_one_bone_idx), joint_one_roll);
+
+	// Apply the rotation to the first joint
+	bone_one_trans = stack->skeleton->global_pose_to_local_pose(joint_one_bone_idx, bone_one_trans);
+	bone_one_trans.origin = Vector3(0, 0, 0);
+	stack->skeleton->set_bone_local_pose_override(joint_one_bone_idx, bone_one_trans, stack->strength, true);
+	stack->skeleton->force_update_bone_children_transforms(joint_one_bone_idx);
+
+	if (use_pole_node) {
+		// Update bone_two_trans so its at the latest position, with the rotation of bone_one_trans taken into account, then look at the target.
+		bone_two_trans = stack->skeleton->local_pose_to_global_pose(joint_two_bone_idx, stack->skeleton->get_bone_local_pose_override(joint_two_bone_idx));
+		stack->skeleton->update_bone_rest_forward_vector(joint_two_bone_idx);
+		Vector3 forward_vector = stack->skeleton->get_bone_axis_forward_vector(joint_two_bone_idx);
+		bone_two_trans.basis.rotate_to_align(forward_vector, bone_two_trans.origin.direction_to(target_trans.origin));
+
+		stack->skeleton->update_bone_rest_forward_vector(joint_two_bone_idx);
+		bone_two_trans.basis.rotate_local(stack->skeleton->get_bone_axis_forward_vector(joint_two_bone_idx), joint_two_roll);
+
+		bone_two_trans = stack->skeleton->global_pose_to_local_pose(joint_two_bone_idx, bone_two_trans);
+		stack->skeleton->set_bone_local_pose_override(joint_two_bone_idx, bone_two_trans, stack->strength, true);
+		stack->skeleton->force_update_bone_children_transforms(joint_two_bone_idx);
+	} else {
+		// Calculate the angles for the second joint using the law of cosigns, make a quaternion with the delta rotation needed to rotate the joint into
+		// alignment, and then apply it to the second joint.
+		real_t ba_bc_0 = Math::acos(CLAMP(bone_two_trans.origin.direction_to(bone_one_trans.origin).dot(bone_two_trans.origin.direction_to(bone_two_tip_trans.origin)), -1, 1));
+		real_t ba_bc_1 = Math::acos(CLAMP((sqr_three_length - sqr_one_length - sqr_two_length) / (-2.0 * joint_one_length * joint_two_length), -1, 1));
+		Quaternion bone_two_quat = bone_two_trans.basis.get_rotation_quaternion();
+		Quaternion rot_1 = Quaternion(bone_two_quat.inverse().xform(axis_0).normalized(), (ba_bc_1 - ba_bc_0));
+		bone_two_trans.basis.set_quaternion(bone_two_quat * rot_1);
+
+		stack->skeleton->update_bone_rest_forward_vector(joint_two_bone_idx);
+		bone_two_trans.basis.rotate_local(stack->skeleton->get_bone_axis_forward_vector(joint_two_bone_idx), joint_two_roll);
+
+		bone_two_trans = stack->skeleton->global_pose_to_local_pose(joint_two_bone_idx, bone_two_trans);
+		bone_two_trans.origin = Vector3(0, 0, 0);
+		stack->skeleton->set_bone_local_pose_override(joint_two_bone_idx, bone_two_trans, stack->strength, true);
+		stack->skeleton->force_update_bone_children_transforms(joint_two_bone_idx);
+	}
+}
+
+void SkeletonModification3DTwoBoneIK::_setup_modification(SkeletonModificationStack3D *p_stack) {
+	stack = p_stack;
+
+	if (stack != nullptr) {
+		is_setup = true;
+		execution_error_found = false;
+		update_cache_target();
+		update_cache_tip();
+	}
+}
+
+void SkeletonModification3DTwoBoneIK::update_cache_target() {
+	if (!is_setup || !stack) {
+		_print_execution_error(true, "Cannot update target cache: modification is not properly setup!");
+		return;
+	}
+
+	target_node_cache = ObjectID();
+	if (stack->skeleton) {
+		if (stack->skeleton->is_inside_tree() && target_node.is_empty() == false) {
+			if (stack->skeleton->has_node(target_node)) {
+				Node *node = stack->skeleton->get_node(target_node);
+				ERR_FAIL_COND_MSG(!node || stack->skeleton == node,
+						"Cannot update target cache: Target node is this modification's skeleton or cannot be found. Cannot execute modification");
+				ERR_FAIL_COND_MSG(!node->is_inside_tree(),
+						"Cannot update target cache: Target node is not in the scene tree. Cannot execute modification!");
+				target_node_cache = node->get_instance_id();
+
+				execution_error_found = false;
+			}
+		}
+	}
+}
+
+void SkeletonModification3DTwoBoneIK::update_cache_tip() {
+	if (!is_setup || !stack) {
+		_print_execution_error(true, "Cannot update tip cache: modification is not properly setup!");
+		return;
+	}
+
+	tip_node_cache = ObjectID();
+	if (stack->skeleton) {
+		if (stack->skeleton->is_inside_tree()) {
+			if (stack->skeleton->has_node(tip_node)) {
+				Node *node = stack->skeleton->get_node(tip_node);
+				ERR_FAIL_COND_MSG(!node || stack->skeleton == node,
+						"Cannot update tip cache: Tip node is this modification's skeleton or cannot be found!");
+				ERR_FAIL_COND_MSG(!node->is_inside_tree(),
+						"Cannot update tip cache: Tip node is not in the scene tree. Cannot execute modification!");
+				tip_node_cache = node->get_instance_id();
+
+				execution_error_found = false;
+			}
+		}
+	}
+}
+
+void SkeletonModification3DTwoBoneIK::update_cache_pole() {
+	if (!is_setup || !stack) {
+		_print_execution_error(true, "Cannot update pole cache: modification is not properly setup!");
+		return;
+	}
+
+	pole_node_cache = ObjectID();
+	if (stack->skeleton) {
+		if (stack->skeleton->is_inside_tree()) {
+			if (stack->skeleton->has_node(pole_node)) {
+				Node *node = stack->skeleton->get_node(pole_node);
+				ERR_FAIL_COND_MSG(!node || stack->skeleton == node,
+						"Cannot update pole cache: Pole node is this modification's skeleton or cannot be found!");
+				ERR_FAIL_COND_MSG(!node->is_inside_tree(),
+						"Cannot update pole cache: Pole node is not in the scene tree. Cannot execute modification!");
+				pole_node_cache = node->get_instance_id();
+
+				execution_error_found = false;
+			}
+		}
+	}
+}
+
+void SkeletonModification3DTwoBoneIK::set_target_node(const NodePath &p_target_node) {
+	target_node = p_target_node;
+	update_cache_target();
+}
+
+NodePath SkeletonModification3DTwoBoneIK::get_target_node() const {
+	return target_node;
+}
+
+void SkeletonModification3DTwoBoneIK::set_use_tip_node(const bool p_use_tip_node) {
+	use_tip_node = p_use_tip_node;
+	notify_property_list_changed();
+}
+
+bool SkeletonModification3DTwoBoneIK::get_use_tip_node() const {
+	return use_tip_node;
+}
+
+void SkeletonModification3DTwoBoneIK::set_tip_node(const NodePath &p_tip_node) {
+	tip_node = p_tip_node;
+	update_cache_tip();
+}
+
+NodePath SkeletonModification3DTwoBoneIK::get_tip_node() const {
+	return tip_node;
+}
+
+void SkeletonModification3DTwoBoneIK::set_use_pole_node(const bool p_use_pole_node) {
+	use_pole_node = p_use_pole_node;
+	notify_property_list_changed();
+}
+
+bool SkeletonModification3DTwoBoneIK::get_use_pole_node() const {
+	return use_pole_node;
+}
+
+void SkeletonModification3DTwoBoneIK::set_pole_node(const NodePath &p_pole_node) {
+	pole_node = p_pole_node;
+	update_cache_pole();
+}
+
+NodePath SkeletonModification3DTwoBoneIK::get_pole_node() const {
+	return pole_node;
+}
+
+void SkeletonModification3DTwoBoneIK::set_auto_calculate_joint_length(bool p_calculate) {
+	auto_calculate_joint_length = p_calculate;
+	if (p_calculate) {
+		calculate_joint_lengths();
+	}
+	notify_property_list_changed();
+}
+
+bool SkeletonModification3DTwoBoneIK::get_auto_calculate_joint_length() const {
+	return auto_calculate_joint_length;
+}
+
+void SkeletonModification3DTwoBoneIK::calculate_joint_lengths() {
+	if (!is_setup) {
+		return; // fail silently, as we likely just loaded the scene.
+	}
+	ERR_FAIL_COND_MSG(!stack || stack->skeleton == nullptr,
+			"Modification is not setup and therefore cannot calculate joint lengths!");
+	ERR_FAIL_COND_MSG(joint_one_bone_idx <= -1 || joint_two_bone_idx <= -1,
+			"One of the bones in the TwoBoneIK modification are not set! Cannot calculate joint lengths!");
+
+	Transform3D bone_one_rest_trans = stack->skeleton->get_bone_global_pose(joint_one_bone_idx);
+	Transform3D bone_two_rest_trans = stack->skeleton->get_bone_global_pose(joint_two_bone_idx);
+
+	joint_one_length = bone_one_rest_trans.origin.distance_to(bone_two_rest_trans.origin);
+
+	if (use_tip_node) {
+		if (tip_node_cache.is_null()) {
+			update_cache_tip();
+			WARN_PRINT("Tip cache is out of date. Updating...");
+		}
+
+		Node3D *tip = Object::cast_to<Node3D>(ObjectDB::get_instance(tip_node_cache));
+		if (tip) {
+			Transform3D bone_tip_trans = stack->skeleton->world_transform_to_global_pose(tip->get_global_transform());
+			joint_two_length = bone_two_rest_trans.origin.distance_to(bone_tip_trans.origin);
+		}
+	} else {
+		// Attempt to use children bones to get the length
+		Vector<int> bone_two_children = stack->skeleton->get_bone_children(joint_two_bone_idx);
+		if (bone_two_children.size() > 0) {
+			joint_two_length = 0;
+			for (int i = 0; i < bone_two_children.size(); i++) {
+				joint_two_length += bone_two_rest_trans.origin.distance_to(
+						stack->skeleton->local_pose_to_global_pose(bone_two_children[i], stack->skeleton->get_bone_rest(bone_two_children[i])).origin);
+			}
+			joint_two_length = joint_two_length / bone_two_children.size();
+		} else {
+			WARN_PRINT("TwoBoneIK modification: Cannot auto calculate length for joint 2! Auto setting the length to 1...");
+			joint_two_length = 1.0;
+		}
+	}
+	execution_error_found = false;
+}
+
+void SkeletonModification3DTwoBoneIK::set_joint_one_bone_name(String p_bone_name) {
+	joint_one_bone_name = p_bone_name;
+	if (stack && stack->skeleton) {
+		joint_one_bone_idx = stack->skeleton->find_bone(p_bone_name);
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+String SkeletonModification3DTwoBoneIK::get_joint_one_bone_name() const {
+	return joint_one_bone_name;
+}
+
+void SkeletonModification3DTwoBoneIK::set_joint_one_bone_idx(int p_bone_idx) {
+	joint_one_bone_idx = p_bone_idx;
+	if (stack && stack->skeleton) {
+		joint_one_bone_name = stack->skeleton->get_bone_name(p_bone_idx);
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+int SkeletonModification3DTwoBoneIK::get_joint_one_bone_idx() const {
+	return joint_one_bone_idx;
+}
+
+void SkeletonModification3DTwoBoneIK::set_joint_one_length(real_t p_length) {
+	joint_one_length = p_length;
+}
+
+real_t SkeletonModification3DTwoBoneIK::get_joint_one_length() const {
+	return joint_one_length;
+}
+
+void SkeletonModification3DTwoBoneIK::set_joint_two_bone_name(String p_bone_name) {
+	joint_two_bone_name = p_bone_name;
+	if (stack && stack->skeleton) {
+		joint_two_bone_idx = stack->skeleton->find_bone(p_bone_name);
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+String SkeletonModification3DTwoBoneIK::get_joint_two_bone_name() const {
+	return joint_two_bone_name;
+}
+
+void SkeletonModification3DTwoBoneIK::set_joint_two_bone_idx(int p_bone_idx) {
+	joint_two_bone_idx = p_bone_idx;
+	if (stack && stack->skeleton) {
+		joint_two_bone_name = stack->skeleton->get_bone_name(p_bone_idx);
+	}
+	execution_error_found = false;
+	notify_property_list_changed();
+}
+
+int SkeletonModification3DTwoBoneIK::get_joint_two_bone_idx() const {
+	return joint_two_bone_idx;
+}
+
+void SkeletonModification3DTwoBoneIK::set_joint_two_length(real_t p_length) {
+	joint_two_length = p_length;
+}
+
+real_t SkeletonModification3DTwoBoneIK::get_joint_two_length() const {
+	return joint_two_length;
+}
+
+void SkeletonModification3DTwoBoneIK::set_joint_one_roll(real_t p_roll) {
+	joint_one_roll = p_roll;
+}
+
+real_t SkeletonModification3DTwoBoneIK::get_joint_one_roll() const {
+	return joint_one_roll;
+}
+
+void SkeletonModification3DTwoBoneIK::set_joint_two_roll(real_t p_roll) {
+	joint_two_roll = p_roll;
+}
+
+real_t SkeletonModification3DTwoBoneIK::get_joint_two_roll() const {
+	return joint_two_roll;
+}
+
+void SkeletonModification3DTwoBoneIK::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("set_target_node", "target_nodepath"), &SkeletonModification3DTwoBoneIK::set_target_node);
+	ClassDB::bind_method(D_METHOD("get_target_node"), &SkeletonModification3DTwoBoneIK::get_target_node);
+
+	ClassDB::bind_method(D_METHOD("set_use_pole_node", "use_pole_node"), &SkeletonModification3DTwoBoneIK::set_use_pole_node);
+	ClassDB::bind_method(D_METHOD("get_use_pole_node"), &SkeletonModification3DTwoBoneIK::get_use_pole_node);
+	ClassDB::bind_method(D_METHOD("set_pole_node", "pole_nodepath"), &SkeletonModification3DTwoBoneIK::set_pole_node);
+	ClassDB::bind_method(D_METHOD("get_pole_node"), &SkeletonModification3DTwoBoneIK::get_pole_node);
+
+	ClassDB::bind_method(D_METHOD("set_use_tip_node", "use_tip_node"), &SkeletonModification3DTwoBoneIK::set_use_tip_node);
+	ClassDB::bind_method(D_METHOD("get_use_tip_node"), &SkeletonModification3DTwoBoneIK::get_use_tip_node);
+	ClassDB::bind_method(D_METHOD("set_tip_node", "tip_nodepath"), &SkeletonModification3DTwoBoneIK::set_tip_node);
+	ClassDB::bind_method(D_METHOD("get_tip_node"), &SkeletonModification3DTwoBoneIK::get_tip_node);
+
+	ClassDB::bind_method(D_METHOD("set_auto_calculate_joint_length", "auto_calculate_joint_length"), &SkeletonModification3DTwoBoneIK::set_auto_calculate_joint_length);
+	ClassDB::bind_method(D_METHOD("get_auto_calculate_joint_length"), &SkeletonModification3DTwoBoneIK::get_auto_calculate_joint_length);
+
+	ClassDB::bind_method(D_METHOD("set_joint_one_bone_name", "bone_name"), &SkeletonModification3DTwoBoneIK::set_joint_one_bone_name);
+	ClassDB::bind_method(D_METHOD("get_joint_one_bone_name"), &SkeletonModification3DTwoBoneIK::get_joint_one_bone_name);
+	ClassDB::bind_method(D_METHOD("set_joint_one_bone_idx", "bone_idx"), &SkeletonModification3DTwoBoneIK::set_joint_one_bone_idx);
+	ClassDB::bind_method(D_METHOD("get_joint_one_bone_idx"), &SkeletonModification3DTwoBoneIK::get_joint_one_bone_idx);
+	ClassDB::bind_method(D_METHOD("set_joint_one_length", "bone_length"), &SkeletonModification3DTwoBoneIK::set_joint_one_length);
+	ClassDB::bind_method(D_METHOD("get_joint_one_length"), &SkeletonModification3DTwoBoneIK::get_joint_one_length);
+
+	ClassDB::bind_method(D_METHOD("set_joint_two_bone_name", "bone_name"), &SkeletonModification3DTwoBoneIK::set_joint_two_bone_name);
+	ClassDB::bind_method(D_METHOD("get_joint_two_bone_name"), &SkeletonModification3DTwoBoneIK::get_joint_two_bone_name);
+	ClassDB::bind_method(D_METHOD("set_joint_two_bone_idx", "bone_idx"), &SkeletonModification3DTwoBoneIK::set_joint_two_bone_idx);
+	ClassDB::bind_method(D_METHOD("get_joint_two_bone_idx"), &SkeletonModification3DTwoBoneIK::get_joint_two_bone_idx);
+	ClassDB::bind_method(D_METHOD("set_joint_two_length", "bone_length"), &SkeletonModification3DTwoBoneIK::set_joint_two_length);
+	ClassDB::bind_method(D_METHOD("get_joint_two_length"), &SkeletonModification3DTwoBoneIK::get_joint_two_length);
+
+	ClassDB::bind_method(D_METHOD("set_joint_one_roll", "roll"), &SkeletonModification3DTwoBoneIK::set_joint_one_roll);
+	ClassDB::bind_method(D_METHOD("get_joint_one_roll"), &SkeletonModification3DTwoBoneIK::get_joint_one_roll);
+	ClassDB::bind_method(D_METHOD("set_joint_two_roll", "roll"), &SkeletonModification3DTwoBoneIK::set_joint_two_roll);
+	ClassDB::bind_method(D_METHOD("get_joint_two_roll"), &SkeletonModification3DTwoBoneIK::get_joint_two_roll);
+
+	ADD_PROPERTY(PropertyInfo(Variant::NODE_PATH, "target_nodepath", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "Node3D"), "set_target_node", "get_target_node");
+	ADD_GROUP("", "");
+}
+
+SkeletonModification3DTwoBoneIK::SkeletonModification3DTwoBoneIK() {
+	stack = nullptr;
+	is_setup = false;
+}
+
+SkeletonModification3DTwoBoneIK::~SkeletonModification3DTwoBoneIK() {
+}

scene/resources/skeleton_modification_3d_twoboneik.h

@@ -0,0 +1,118 @@
+/*************************************************************************/
+/*  skeleton_modification_3d_twoboneik.h                                 */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "scene/3d/skeleton_3d.h"
+#include "scene/resources/skeleton_modification_3d.h"
+
+#ifndef SKELETONMODIFICATION3DTWOBONEIK_H
+#define SKELETONMODIFICATION3DTWOBONEIK_H
+
+class SkeletonModification3DTwoBoneIK : public SkeletonModification3D {
+	GDCLASS(SkeletonModification3DTwoBoneIK, SkeletonModification3D);
+
+private:
+	NodePath target_node;
+	ObjectID target_node_cache;
+
+	bool use_tip_node = false;
+	NodePath tip_node;
+	ObjectID tip_node_cache;
+
+	bool use_pole_node = false;
+	NodePath pole_node;
+	ObjectID pole_node_cache;
+
+	String joint_one_bone_name = "";
+	int joint_one_bone_idx = -1;
+	String joint_two_bone_name = "";
+	int joint_two_bone_idx = -1;
+
+	bool auto_calculate_joint_length = false;
+	real_t joint_one_length = -1;
+	real_t joint_two_length = -1;
+
+	real_t joint_one_roll = 0;
+	real_t joint_two_roll = 0;
+
+	void update_cache_target();
+	void update_cache_tip();
+	void update_cache_pole();
+
+protected:
+	static void _bind_methods();
+	bool _get(const StringName &p_path, Variant &r_ret) const;
+	bool _set(const StringName &p_path, const Variant &p_value);
+	void _get_property_list(List<PropertyInfo> *p_list) const;
+
+public:
+	virtual void _execute(real_t p_delta) override;
+	virtual void _setup_modification(SkeletonModificationStack3D *p_stack) override;
+
+	void set_target_node(const NodePath &p_target_node);
+	NodePath get_target_node() const;
+
+	void set_use_tip_node(const bool p_use_tip_node);
+	bool get_use_tip_node() const;
+	void set_tip_node(const NodePath &p_tip_node);
+	NodePath get_tip_node() const;
+
+	void set_use_pole_node(const bool p_use_pole_node);
+	bool get_use_pole_node() const;
+	void set_pole_node(const NodePath &p_pole_node);
+	NodePath get_pole_node() const;
+
+	void set_auto_calculate_joint_length(bool p_calculate);
+	bool get_auto_calculate_joint_length() const;
+	void calculate_joint_lengths();
+
+	void set_joint_one_bone_name(String p_bone_name);
+	String get_joint_one_bone_name() const;
+	void set_joint_one_bone_idx(int p_bone_idx);
+	int get_joint_one_bone_idx() const;
+	void set_joint_one_length(real_t p_length);
+	real_t get_joint_one_length() const;
+
+	void set_joint_two_bone_name(String p_bone_name);
+	String get_joint_two_bone_name() const;
+	void set_joint_two_bone_idx(int p_bone_idx);
+	int get_joint_two_bone_idx() const;
+	void set_joint_two_length(real_t p_length);
+	real_t get_joint_two_length() const;
+
+	void set_joint_one_roll(real_t p_roll);
+	real_t get_joint_one_roll() const;
+	void set_joint_two_roll(real_t p_roll);
+	real_t get_joint_two_roll() const;
+
+	SkeletonModification3DTwoBoneIK();
+	~SkeletonModification3DTwoBoneIK();
+};
+
+#endif //SKELETONMODIFICATION3DTWOBONEIK_H

scene/resources/skeleton_modification_stack_3d.cpp

@@ -0,0 +1,222 @@
+/*************************************************************************/
+/*  skeleton_modification_stack_3d.cpp                                   */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "skeleton_modification_stack_3d.h"
+#include "scene/3d/skeleton_3d.h"
+
+///////////////////////////////////////
+// ModificationStack3D
+///////////////////////////////////////
+
+void SkeletonModificationStack3D::_get_property_list(List<PropertyInfo> *p_list) const {
+	for (uint32_t i = 0; i < modifications.size(); i++) {
+		p_list->push_back(
+				PropertyInfo(Variant::OBJECT, "modifications/" + itos(i),
+						PROPERTY_HINT_RESOURCE_TYPE,
+						"SkeletonModification3D",
+						PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_DEFERRED_SET_RESOURCE | PROPERTY_USAGE_DO_NOT_SHARE_ON_DUPLICATE));
+	}
+}
+
+bool SkeletonModificationStack3D::_set(const StringName &p_path, const Variant &p_value) {
+	String path = p_path;
+
+	if (path.begins_with("modifications/")) {
+		int mod_idx = path.get_slicec('/', 1).to_int();
+		set_modification(mod_idx, p_value);
+		return true;
+	}
+	return true;
+}
+
+bool SkeletonModificationStack3D::_get(const StringName &p_path, Variant &r_ret) const {
+	String path = p_path;
+
+	if (path.begins_with("modifications/")) {
+		int mod_idx = path.get_slicec('/', 1).to_int();
+		r_ret = get_modification(mod_idx);
+		return true;
+	}
+	return true;
+}
+
+void SkeletonModificationStack3D::setup() {
+	if (is_setup) {
+		return;
+	}
+
+	if (skeleton != nullptr) {
+		is_setup = true;
+		for (uint32_t i = 0; i < modifications.size(); i++) {
+			if (!modifications[i].is_valid()) {
+				continue;
+			}
+			modifications[i]->_setup_modification(this);
+		}
+	} else {
+		WARN_PRINT("Cannot setup SkeletonModificationStack3D: no skeleton set!");
+	}
+}
+
+void SkeletonModificationStack3D::execute(real_t p_delta, int p_execution_mode) {
+	ERR_FAIL_COND_MSG(!is_setup || skeleton == nullptr || is_queued_for_deletion(),
+			"Modification stack is not properly setup and therefore cannot execute!");
+
+	if (!skeleton->is_inside_tree()) {
+		ERR_PRINT_ONCE("Skeleton is not inside SceneTree! Cannot execute modification!");
+		return;
+	}
+
+	if (!enabled) {
+		return;
+	}
+
+	for (uint32_t i = 0; i < modifications.size(); i++) {
+		if (!modifications[i].is_valid()) {
+			continue;
+		}
+
+		if (modifications[i]->get_execution_mode() == p_execution_mode) {
+			modifications[i]->_execute(p_delta);
+		}
+	}
+}
+
+void SkeletonModificationStack3D::enable_all_modifications(bool p_enabled) {
+	for (uint32_t i = 0; i < modifications.size(); i++) {
+		if (!modifications[i].is_valid()) {
+			continue;
+		}
+		modifications[i]->set_enabled(p_enabled);
+	}
+}
+
+Ref<SkeletonModification3D> SkeletonModificationStack3D::get_modification(int p_mod_idx) const {
+	const int modifications_size = modifications.size();
+	ERR_FAIL_INDEX_V(p_mod_idx, modifications_size, nullptr);
+	return modifications[p_mod_idx];
+}
+
+void SkeletonModificationStack3D::add_modification(Ref<SkeletonModification3D> p_mod) {
+	p_mod->_setup_modification(this);
+	modifications.push_back(p_mod);
+}
+
+void SkeletonModificationStack3D::delete_modification(int p_mod_idx) {
+	const int modifications_size = modifications.size();
+	ERR_FAIL_INDEX(p_mod_idx, modifications_size);
+	modifications.remove(p_mod_idx);
+}
+
+void SkeletonModificationStack3D::set_modification(int p_mod_idx, Ref<SkeletonModification3D> p_mod) {
+	const int modifications_size = modifications.size();
+	ERR_FAIL_INDEX(p_mod_idx, modifications_size);
+
+	if (p_mod == nullptr) {
+		modifications.remove(p_mod_idx);
+	} else {
+		p_mod->_setup_modification(this);
+		modifications[p_mod_idx] = p_mod;
+	}
+}
+
+void SkeletonModificationStack3D::set_modification_count(int p_count) {
+	modifications.resize(p_count);
+	notify_property_list_changed();
+}
+
+int SkeletonModificationStack3D::get_modification_count() const {
+	return modifications.size();
+}
+
+void SkeletonModificationStack3D::set_skeleton(Skeleton3D *p_skeleton) {
+	skeleton = p_skeleton;
+}
+
+Skeleton3D *SkeletonModificationStack3D::get_skeleton() const {
+	return skeleton;
+}
+
+bool SkeletonModificationStack3D::get_is_setup() const {
+	return is_setup;
+}
+
+void SkeletonModificationStack3D::set_enabled(bool p_enabled) {
+	enabled = p_enabled;
+
+	if (!enabled && is_setup && skeleton != nullptr) {
+		skeleton->clear_bones_local_pose_override();
+	}
+}
+
+bool SkeletonModificationStack3D::get_enabled() const {
+	return enabled;
+}
+
+void SkeletonModificationStack3D::set_strength(real_t p_strength) {
+	ERR_FAIL_COND_MSG(p_strength < 0, "Strength cannot be less than zero!");
+	ERR_FAIL_COND_MSG(p_strength > 1, "Strength cannot be more than one!");
+	strength = p_strength;
+}
+
+real_t SkeletonModificationStack3D::get_strength() const {
+	return strength;
+}
+
+void SkeletonModificationStack3D::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("setup"), &SkeletonModificationStack3D::setup);
+	ClassDB::bind_method(D_METHOD("execute", "delta", "execution_mode"), &SkeletonModificationStack3D::execute);
+
+	ClassDB::bind_method(D_METHOD("enable_all_modifications", "enabled"), &SkeletonModificationStack3D::enable_all_modifications);
+	ClassDB::bind_method(D_METHOD("get_modification", "mod_idx"), &SkeletonModificationStack3D::get_modification);
+	ClassDB::bind_method(D_METHOD("add_modification", "modification"), &SkeletonModificationStack3D::add_modification);
+	ClassDB::bind_method(D_METHOD("delete_modification", "mod_idx"), &SkeletonModificationStack3D::delete_modification);
+	ClassDB::bind_method(D_METHOD("set_modification", "mod_idx", "modification"), &SkeletonModificationStack3D::set_modification);
+
+	ClassDB::bind_method(D_METHOD("set_modification_count"), &SkeletonModificationStack3D::set_modification_count);
+	ClassDB::bind_method(D_METHOD("get_modification_count"), &SkeletonModificationStack3D::get_modification_count);
+
+	ClassDB::bind_method(D_METHOD("get_is_setup"), &SkeletonModificationStack3D::get_is_setup);
+
+	ClassDB::bind_method(D_METHOD("set_enabled", "enabled"), &SkeletonModificationStack3D::set_enabled);
+	ClassDB::bind_method(D_METHOD("get_enabled"), &SkeletonModificationStack3D::get_enabled);
+
+	ClassDB::bind_method(D_METHOD("set_strength", "strength"), &SkeletonModificationStack3D::set_strength);
+	ClassDB::bind_method(D_METHOD("get_strength"), &SkeletonModificationStack3D::get_strength);
+
+	ClassDB::bind_method(D_METHOD("get_skeleton"), &SkeletonModificationStack3D::get_skeleton);
+
+	ADD_PROPERTY(PropertyInfo(Variant::BOOL, "enabled"), "set_enabled", "get_enabled");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "strength", PROPERTY_HINT_RANGE, "0, 1, 0.001"), "set_strength", "get_strength");
+	ADD_PROPERTY(PropertyInfo(Variant::INT, "modification_count", PROPERTY_HINT_RANGE, "0, 100, 1"), "set_modification_count", "get_modification_count");
+}
+
+SkeletonModificationStack3D::SkeletonModificationStack3D() {
+}

scene/resources/skeleton_modification_stack_3d.h

@@ -0,0 +1,91 @@
+/*************************************************************************/
+/*  skeleton_modification_stack_3d.h                                     */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef SKELETONMODIFICATIONSTACK3D_H
+#define SKELETONMODIFICATIONSTACK3D_H
+
+#include "core/templates/local_vector.h"
+#include "scene/3d/skeleton_3d.h"
+
+class Skeleton3D;
+class SkeletonModification3D;
+
+class SkeletonModificationStack3D : public Resource {
+	GDCLASS(SkeletonModificationStack3D, Resource);
+	friend class Skeleton3D;
+	friend class SkeletonModification3D;
+
+protected:
+	static void _bind_methods();
+	virtual void _get_property_list(List<PropertyInfo> *p_list) const;
+	virtual bool _set(const StringName &p_path, const Variant &p_value);
+	virtual bool _get(const StringName &p_path, Variant &r_ret) const;
+
+public:
+	Skeleton3D *skeleton = nullptr;
+	bool is_setup = false;
+	bool enabled = false;
+	real_t strength = 1.0;
+
+	enum EXECUTION_MODE {
+		execution_mode_process,
+		execution_mode_physics_process,
+	};
+
+	LocalVector<Ref<SkeletonModification3D>> modifications = LocalVector<Ref<SkeletonModification3D>>();
+	int modifications_count = 0;
+
+	virtual void setup();
+	virtual void execute(real_t p_delta, int p_execution_mode);
+
+	void enable_all_modifications(bool p_enable);
+	Ref<SkeletonModification3D> get_modification(int p_mod_idx) const;
+	void add_modification(Ref<SkeletonModification3D> p_mod);
+	void delete_modification(int p_mod_idx);
+	void set_modification(int p_mod_idx, Ref<SkeletonModification3D> p_mod);
+
+	void set_modification_count(int p_count);
+	int get_modification_count() const;
+
+	void set_skeleton(Skeleton3D *p_skeleton);
+	Skeleton3D *get_skeleton() const;
+
+	bool get_is_setup() const;
+
+	void set_enabled(bool p_enabled);
+	bool get_enabled() const;
+
+	void set_strength(real_t p_strength);
+	real_t get_strength() const;
+
+	SkeletonModificationStack3D();
+};
+
+#endif // SKELETONMODIFICATIONSTACK3D_H

scene/scene_string_names.cpp

@@ -63,6 +63,7 @@ SceneStringNames::SceneStringNames() {
 	animation_started = StaticCString::create("animation_started");
 
 	pose_updated = StaticCString::create("pose_updated");
+	bone_pose_changed = StaticCString::create("bone_pose_changed");
 
 	mouse_entered = StaticCString::create("mouse_entered");
 	mouse_exited = StaticCString::create("mouse_exited");

scene/scene_string_names.h

@@ -98,6 +98,7 @@ public:
 	StringName animation_started;
 
 	StringName pose_updated;
+	StringName bone_pose_changed;
 
 	StringName body_shape_entered;
 	StringName body_entered;