Fixed single bone IK with flipping and y-up coordinate systems.

spine-as3/spine-as3/src/spine/IkConstraint.as

@@ -77,7 +77,9 @@ public class IkConstraint {
 	static public function apply1 (bone:Bone, targetX:Number, targetY:Number, alpha:Number) : void {
 		var parentRotation:Number = (!bone._data.inheritRotation || bone._parent == null) ? 0 : bone._parent._worldRotation;
 		var rotation:Number = bone.rotation;
-		var rotationIK:Number = Math.atan2(targetY - bone._worldY, targetX - bone._worldX) * radDeg - parentRotation;
+		var rotationIK:Number = Math.atan2(targetY - bone._worldY, targetX - bone._worldX) * radDeg;
+		if (bone._worldFlipX != (bone._worldFlipY != Bone.yDown)) rotationIK = -rotationIK;
+		rotationIK -= parentRotation;
 		bone.rotationIK = rotation + (rotationIK - rotation) * alpha;
 	}
 

spine-c/src/spine/IkConstraint.c

@@ -69,7 +69,9 @@ void spIkConstraint_apply (spIkConstraint* self) {
 void spIkConstraint_apply1 (spBone* bone, float targetX, float targetY, float alpha) {
 	float parentRotation = (!bone->data->inheritRotation || !bone->parent) ? 0 : bone->parent->worldRotation;
 	float rotation = bone->rotation;
-	float rotationIK = ATAN2(targetY - bone->worldY, targetX - bone->worldX) * RAD_DEG - parentRotation;
+	float rotationIK = ATAN2(targetY - bone->worldY, targetX - bone->worldX) * RAD_DEG;
+	if (bone->worldFlipX != (bone->worldFlipY != yDown)) rotationIK = -rotationIK;
+	rotationIK -= parentRotation;
 	bone->rotationIK = rotation + (rotationIK - rotation) * alpha;
 }
 

spine-csharp/src/IkConstraint.cs

@@ -82,7 +82,9 @@ namespace Spine {
 		static public void apply (Bone bone, float targetX, float targetY, float alpha) {
 			float parentRotation = (!bone.data.inheritRotation || bone.parent == null) ? 0 : bone.parent.worldRotation;
 			float rotation = bone.rotation;
-			float rotationIK = (float)Math.Atan2(targetY - bone.worldY, targetX - bone.worldX) * radDeg - parentRotation;
+			float rotationIK = (float)Math.Atan2(targetY - bone.worldY, targetX - bone.worldX) * radDeg;
+			if (bone.worldFlipX != (bone.worldFlipY != Bone.yDown)) rotationIK = -rotationIK;
+			rotationIK -= parentRotation;
 			bone.rotationIK = rotation + (rotationIK - rotation) * alpha;
 		}
 

spine-js/spine.js

@@ -226,7 +226,9 @@ spine.IkConstraint.prototype = {
 spine.IkConstraint.apply1 = function (bone, targetX, targetY, alpha) {
 	var parentRotation = (!bone.data.inheritRotation || !bone.parent) ? 0 : bone.parent.worldRotation;
 	var rotation = bone.rotation;
-	var rotationIK = Math.atan2(targetY - bone.worldY, targetX - bone.worldX) * spine.radDeg - parentRotation;
+	var rotationIK = Math.atan2(targetY - bone.worldY, targetX - bone.worldX) * spine.radDeg;
+	if (bone.worldFlipX != (bone.worldFlipY != spine.Bone.yDown)) rotationIK = -rotationIK;
+	rotationIK -= parentRotation;
 	bone.rotationIK = rotation + (rotationIK - rotation) * alpha;
 };
 /** Adjusts the parent and child bone rotations so the tip of the child is as close to the target position as possible. The

spine-lua/IkConstraint.lua

@@ -72,7 +72,11 @@ function IkConstraint.apply1 (bone, targetX, targetY, alpha)
 		parentRotation = bone.parent.worldRotation
 	end
 	local rotation = bone.rotation
-	local rotationIK = math.atan2(targetY - bone.worldY, targetX - bone.worldX) * radDeg - parentRotation
+	local rotationIK = math.atan2(targetY - bone.worldY, targetX - bone.worldX) * radDeg
+	if bone.worldFlipX ~= bone.worldFlipY then
+		rotationIK = -rotationIK
+	end
+	rotationIK = rotationIK - parentRotation
 	bone.rotationIK = rotation + (rotationIK - rotation) * alpha
 end