heres my code im not sure how to get the world transform of the compoundshapes child
here my code
// make compound
btCompoundShape* g1 = new btCompoundShape();
btCollisionShape* boxshape = new btBoxShape(btVector3(20, 20, 20));
g1->addChildShape( startTransform , boxshape );
// add rigid body to world
g1->calculateLocalInertia(commass, cominer);
btRigidBody::btRigidBodyConstructionInfo fallRigidBodyCI(commass,comMotionState, g1, cominer);
btRigidBody* comRigidBody = new btRigidBody(fallRigidBodyCI);
dynamicsWorld->addRigidBody(comRigidBody);
// this all works fine this is where im not sure what to do
btTransform 2;
// getchildtransform returns the local transform on the child shape
btTransform 1 = g1->getChildTransform(1);
comRigidBody->getMotionState()->getWorldTransform(2)
// how do i calculate the child world transform from the compoundrigidbody world transform and the child local position
btTransform childworldtrans = 2 * 1;