RigidBody2D: add and bind get_inertia() method.

You can't set this value very well, since it's automatically computed
from the mass and the collision shapes. But since the values are higher
than many people might suspect, so being able to read it helps estimate
the amount of torque you might need to apply.

doc/base/classes.xml

@@ -24867,13 +24867,15 @@ This method controls whether the position between two cached points is interpola
 		</constant>
 		<constant name="BODY_PARAM_MASS" value="2">
 		</constant>
-		<constant name="BODY_PARAM_GRAVITY_SCALE" value="3">
+		<constant name="BODY_PARAM_INERTIA" value="3">
 		</constant>
-		<constant name="BODY_PARAM_LINEAR_DAMP" value="4">
+		<constant name="BODY_PARAM_GRAVITY_SCALE" value="4">
 		</constant>
-		<constant name="BODY_PARAM_ANGULAR_DAMP" value="5">
+		<constant name="BODY_PARAM_LINEAR_DAMP" value="5">
 		</constant>
-		<constant name="BODY_PARAM_MAX" value="6">
+		<constant name="BODY_PARAM_ANGULAR_DAMP" value="6">
+		</constant>
+		<constant name="BODY_PARAM_MAX" value="7">
 		</constant>
 		<constant name="BODY_STATE_TRANSFORM" value="0">
 		</constant>
@@ -30035,6 +30037,13 @@ This method controls whether the position between two cached points is interpola
 			Return the body mass.
 			</description>
 		</method>
+		<method name="get_inertia" qualifiers="const">
+			<return type="float">
+			</return>
+			<description>
+			Return the body's moment of inertia. This is automatically computed from the mass and the shapes, so you can't set it. But at least you can find out what it's current value is...
+			</description>
+		</method>
 		<method name="set_weight">
 			<argument index="0" name="weight" type="float">
 			</argument>
@@ -30238,12 +30247,14 @@ This method controls whether the position between two cached points is interpola
 			<argument index="0" name="torque" type="float">
 			</argument>
 			<description>
+			Set a constant torque which will be applied to this body.
 			</description>
 		</method>
 		<method name="get_applied_torque" qualifiers="const">
 			<return type="float">
 			</return>
 			<description>
+			Return the torque which is being applied to this body.
 			</description>
 		</method>
 		<method name="set_sleeping">

scene/2d/physics_body_2d.cpp

@@ -602,6 +602,11 @@ real_t RigidBody2D::get_mass() const{
 	return mass;
 }
 
+real_t RigidBody2D::get_inertia() const{
+
+	return Physics2DServer::get_singleton()->body_get_param(get_rid(),Physics2DServer::BODY_PARAM_INERTIA);
+}
+
 void RigidBody2D::set_weight(real_t p_weight){
 
 	set_mass(p_weight/9.8);
@@ -868,6 +873,8 @@ void RigidBody2D::_bind_methods() {
 	ObjectTypeDB::bind_method(_MD("set_mass","mass"),&RigidBody2D::set_mass);
 	ObjectTypeDB::bind_method(_MD("get_mass"),&RigidBody2D::get_mass);
 
+	ObjectTypeDB::bind_method(_MD("get_inertia"),&RigidBody2D::get_inertia);
+
 	ObjectTypeDB::bind_method(_MD("set_weight","weight"),&RigidBody2D::set_weight);
 	ObjectTypeDB::bind_method(_MD("get_weight"),&RigidBody2D::get_weight);
 

scene/2d/physics_body_2d.h

@@ -217,6 +217,8 @@ public:
 	void set_mass(real_t p_mass);
 	real_t get_mass() const;
 
+	real_t get_inertia() const;  // read-only: auto-computed from mass & shapes.
+
 	void set_weight(real_t p_weight);
 	real_t get_weight() const;
 

servers/physics_2d/body_2d_sw.cpp

@@ -186,6 +186,10 @@ float Body2DSW::get_param(Physics2DServer::BodyParameter p_param) const {
 		case Physics2DServer::BODY_PARAM_MASS: {
 			return mass;
 		} break;
+		case Physics2DServer::BODY_PARAM_INERTIA: {
+			if(_inv_inertia == 0) return INFINITY;
+			else return 1.0 / _inv_inertia;
+		} break;
 		case Physics2DServer::BODY_PARAM_GRAVITY_SCALE: {
 			return gravity_scale;
 		} break;

servers/physics_2d_server.cpp

@@ -677,6 +677,7 @@ void Physics2DServer::_bind_methods() {
 	BIND_CONSTANT( BODY_PARAM_BOUNCE );
 	BIND_CONSTANT( BODY_PARAM_FRICTION );
 	BIND_CONSTANT( BODY_PARAM_MASS );
+	BIND_CONSTANT( BODY_PARAM_INERTIA );
 	BIND_CONSTANT( BODY_PARAM_GRAVITY_SCALE );
 	BIND_CONSTANT( BODY_PARAM_LINEAR_DAMP);
 	BIND_CONSTANT( BODY_PARAM_ANGULAR_DAMP);

servers/physics_2d_server.h

@@ -421,6 +421,7 @@ public:
 		BODY_PARAM_BOUNCE,
 		BODY_PARAM_FRICTION,
 		BODY_PARAM_MASS, ///< unused for static, always infinite
+		BODY_PARAM_INERTIA,  // read-only: computed from mass & shapes
 		BODY_PARAM_GRAVITY_SCALE,
 		BODY_PARAM_LINEAR_DAMP,
 		BODY_PARAM_ANGULAR_DAMP,