protected void applyAnisotropicFriction( btCollisionObject colObj, ref btVector3 frictionDirection
, btCollisionObject.AnisotropicFrictionFlags frictionMode )
{
if( colObj != null && colObj.hasAnisotropicFriction( frictionMode ) )
{
// transform to local coordinates
btVector3 loc_lateral;// = frictionDirection * colObj.getWorldTransform().getBasis();
colObj.m_worldTransform.m_basis.Apply( ref frictionDirection, out loc_lateral );
//btVector3 friction_scaling; = colObj.getAnisotropicFriction();
//apply anisotropic friction
loc_lateral.Mult( ref colObj.m_anisotropicFriction, out loc_lateral );
// ... and transform it back to global coordinates
colObj.m_worldTransform.m_basis.Apply( ref loc_lateral, out frictionDirection );
//frictionDirection = colObj.getWorldTransform().getBasis() * loc_lateral;
}
}