godot/modules/bullet/godot_motion_state.h

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/*  godot_motion_state.h                                                 */
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#ifndef GODOT_MOTION_STATE_H
#define GODOT_MOTION_STATE_H

#include "rigid_body_bullet.h"

#include <LinearMath/btMotionState.h>

class RigidBodyBullet;

// This class is responsible to move kinematic actor
// and sincronize rendering engine with Bullet
/// DOC:
/// http://www.bulletphysics.org/mediawiki-1.5.8/index.php/MotionStates#What.27s_a_MotionState.3F
class GodotMotionState : public btMotionState {
	/// This data is used to store the new world position for kinematic body
	btTransform bodyKinematicWorldTransf;
	/// This data is used to store last world position
	btTransform bodyCurrentWorldTransform;

	RigidBodyBullet *owner = nullptr;

public:
	GodotMotionState(RigidBodyBullet *p_owner) :
			bodyKinematicWorldTransf(btMatrix3x3(1., 0., 0., 0., 1., 0., 0., 0., 1.), btVector3(0., 0., 0.)),
			bodyCurrentWorldTransform(btMatrix3x3(1., 0., 0., 0., 1., 0., 0., 0., 1.), btVector3(0., 0., 0.)),
			owner(p_owner) {}

	/// IMPORTANT DON'T USE THIS FUNCTION TO KNOW THE CURRENT BODY TRANSFORM
	/// This class is used internally by Bullet
	/// Use GodotMotionState::getCurrentWorldTransform to know current position
	///
	/// This function is used by Bullet to get the position of object in the world
	/// if the body is kinematic Bullet will move the object to this location
	/// if the body is static Bullet doesn't move at all
	virtual void getWorldTransform(btTransform &worldTrans) const {
		worldTrans = bodyKinematicWorldTransf;
	}

	/// IMPORTANT: to move the body use: moveBody
	/// IMPORTANT: DON'T CALL THIS FUNCTION, IT IS CALLED BY BULLET TO UPDATE RENDERING ENGINE
	///
	/// This function is called each time by Bullet and set the current position of body
	/// inside the physics world.
	/// Don't allow Godot rendering scene takes world transform from this object because
	/// the correct transform is set by Bullet only after the last step when there are sub steps
	/// This function must update Godot transform rendering scene for this object.
	virtual void setWorldTransform(const btTransform &worldTrans) {
		bodyCurrentWorldTransform = worldTrans;

		owner->notify_transform_changed();
	}

public:
	/// Use this function to move kinematic body
	/// -- or set initial transform before body creation.
	void moveBody(const btTransform &newWorldTransform) {
		bodyKinematicWorldTransf = newWorldTransform;
	}

	/// It returns the current body transform from last Bullet update
	const btTransform &getCurrentWorldTransform() const {
		return bodyCurrentWorldTransform;
	}
};

#endif // GODOT_MOTION_STATE_H