set centerOfMassOffset in btDefaultMotionState

[xinguang]

Hi,

I am new to bullet and encounter a seeminly trivial problem. Is it a bug in the btDefaultMotionState or by design?

virtual void getWorldTransform(btTransform& centerOfMassWorldTrans ) const
{
centerOfMassWorldTrans = m_centerOfMassOffset.inverse() * m_graphicsWorldTrans ;
}

///synchronizes world transform from physics to user
///Bullet only calls the update of worldtransform for active objects
virtual void setWorldTransform(const btTransform& centerOfMassWorldTrans)
{
m_graphicsWorldTrans = centerOfMassWorldTrans * m_centerOfMassOffset ;
}

In the above, if m_centerOfMassOffset is not the identity, the following assertion will be false

btDefaultMotionState motionState( startTrans, centerOfMassOffset );

btTransform center1;
btTransform center2;
motionState.getWorldTransform( center1 );
motionState.setWorldTransform( center1 );
motionState.getWorldTransform( center2 );

assert( isEqual( center1, center2 ) );

Should setWorldTransform be
m_graphicsWorldTrans = m_centerOfMassOffset * centerOfMassWorldTrans;
instead of
m_graphicsWorldTrans = centerOfMassWorldTrans * m_centerOfMassOffset ;

Thanks,

xinguang