MotionState Data Structure

[Herleson]

Hello Friends,

Going deeper in Bullet studies, I was studying MotionState, what is an incredible feature. However, the Manual and Wiki has a introduction perspective of it. I was wondering how MotionState stores and processes object data. What is the Data Structure used by Bullet to handle object data in MotionState? Is there any link that gives more details about it?

Regards!

[Antonz]

What are you really want to achieve? btMotionState is just a two-funcs interfaces: one for getting "user" matrix from user to physics (usually kinematic objects), and one for setting it from physics to user (dynamic objects).

Obviously it's better to extend/wrap this class for additional functionality. I'm using such class for a subscription-based notifications. Subscribers that want physics->user transform update notification are inherit from IMotionStateCallback . Small note: I'm using Marmalade SDK CIwArray container here, you should update this code for STL or other containers a bit.

Code: Select all

//===========================================================================
class IMotionStateCallback
{
public:
	virtual void		OnMotionStateChanged ( const btTransform& worldTrans ) = 0;
};

//===========================================================================
class MotionState : public btMotionState
{
public:
						MotionState			( const btTransform& startTrans = btTransform::getIdentity())
						: worldTrans_		( startTrans )
						, stateChangedCallbacks_ ()
						{ }

	//---------------------------------------------------------------------------
	// btMotionState interface.

	/// Synchronizes world transform from user to physics
	virtual void		getWorldTransform	( btTransform& centerOfMassWorldTrans ) const 
	{
		centerOfMassWorldTrans = worldTrans_;
	}

	///synchronizes world transform from physics to user
	///Bullet only calls the update of worldtransform for active objects
	virtual void		setWorldTransform	( const btTransform& centerOfMassWorldTrans )
	{
		worldTrans_ = centerOfMassWorldTrans;
		if (!stateChangedCallbacks_.empty())
		{
			for (MotionStateCallbacks_t::const_iterator it = stateChangedCallbacks_.begin(),
					it_end = stateChangedCallbacks_.end(); it != it_end; ++it)
			{
				(*it)->OnMotionStateChanged (worldTrans_);
			}
		}
	}

	// Internal interface.
	const btTransform&	getWorldTransform	() const
	{
		return worldTrans_;
	}

	void				setWorldTransform	( const btTransform& centerOfMassWorldTrans
											, bool invokeCallbacks = true )
	{
		worldTrans_ = centerOfMassWorldTrans;
		if (invokeCallbacks && !stateChangedCallbacks_.empty())
		{
			for (MotionStateCallbacks_t::const_iterator it = stateChangedCallbacks_.begin(),
					it_end = stateChangedCallbacks_.end(); it != it_end; ++it)
			{
				(*it)->OnMotionStateChanged (worldTrans_);
			}
		}
	}

	void				AddMotionStateCallback ( IMotionStateCallback* callback )
	{
		IwAssert(PHYSICS, stateChangedCallbacks_.find ( callback ) < 0);
		stateChangedCallbacks_.push_back ( callback );
	}

	void				RemoveMotionStateCallback ( IMotionStateCallback* callback )
	{
		IwAssert(PHYSICS, stateChangedCallbacks_.find (callback) >= 0);
		stateChangedCallbacks_.find_and_remove_fast ( callback );
	}

private:
	typedef CIwArray<IMotionStateCallback*>	MotionStateCallbacks_t;

	btTransform								worldTrans_;
	MotionStateCallbacks_t					stateChangedCallbacks_;
};