void RigidBodyDerivatives( const float t, const void *clientData, const float *state, float *derivatives ) {
	const idPhysics_RigidBody *p = (idPhysics_RigidBody *) clientData;
	rigidBodyIState_t *s = (rigidBodyIState_t *) state;
	// NOTE: this struct should be build conform rigidBodyIState_t
	struct rigidBodyDerivatives_s {
		idVec3				linearVelocity;
		idMat3				angularMatrix;
		idVec3				force;
		idVec3				torque;
	} *d = (struct rigidBodyDerivatives_s *) derivatives;
	idVec3 angularVelocity;
	idMat3 inverseWorldInertiaTensor;

	inverseWorldInertiaTensor = s->orientation * p->inverseInertiaTensor * s->orientation.Transpose();
	angularVelocity = inverseWorldInertiaTensor * s->angularMomentum;
	// derivatives
	d->linearVelocity = p->inverseMass * s->linearMomentum;
	d->angularMatrix = SkewSymmetric( angularVelocity ) * s->orientation;
	d->force = - p->linearFriction * s->linearMomentum + p->current.externalForce;
	d->torque = - p->angularFriction * s->angularMomentum + p->current.externalTorque;
}