Help with ball platform game

[d.oratio22]

Hi,
First of all congrats to everyone involved into the creation and maintenance of the bullet library.
I am trying to make a small game using bullet.
You control a flat box which you can rotate (pitch,roll) using the mouse. On top of the box is a ball.
So you have to balance the ball not fall outside.
I am trying to work out the mechanics so thats why the gameplay is not that great

I used a modification of the BasicDemo, with a few bits of the CCDDemo.
In essence I use a KINEMATIC boxshape as the platform and a sphere shape as a dynamic object. I change every frame the rotation of the kinematic object. the Gravity is 0,-10,0.

The problem is that If I rotate slightly the box the ball does not follow the box smoothly but makes little bounces giving the impression of unsmooth ball motion. If you make a big rotation the ball goes completely out of control.
This looks very unnatural and I am looking for a way to make the ball stick always onto the platform and to disallow bouncing. Any pointers how I could do that.

I am attaching a small executable which shows what I am taking about. Try to use the mouse to make the ball go from the left to the right side, or any sudden movements and you will see what I talking about.

Thanks for any help in advance
Oratio

Here are some various peaces of code which I use:

Code: Select all

void BasicDemo::clientMoveAndDisplay()
{
...
	//KINEMATIC GROUND
	btQuaternion kinRotationZ(btVector3(0,0,1),rotZ);
	btQuaternion kinRotationX(btVector3(1,0,0),rotX);

	//kinematic object
	btCollisionObject* colObj = m_dynamicsWorld->getCollisionObjectArray()[0];
	
	if (btRigidBody::upcast(colObj))
	{
		btTransform newTrans;
		btTransform newTrans2(kinRotationX);
		btRigidBody::upcast(colObj)->getMotionState()->getWorldTransform(newTrans);
		newTrans.setRotation (kinRotationZ);
		newTrans *= newTrans2;
		btRigidBody::upcast(colObj)->getMotionState()->setWorldTransform(newTrans);
	} 
...
	float dt = m_clock.getTimeMicroseconds() * 0.000001f;
	m_clock.reset();
	int maxSimSubSteps = 1;//m_idle ? 1 : 1;
	if (m_dynamicsWorld)
	    m_dynamicsWorld->stepSimulation(dt, maxSimSubSteps, 1./60);
	 
	renderme(); 
	glFlush();
	glutSwapBuffers();
}

Code: Select all

void	BasicDemo::initPhysics()
{
...
    m_collisionConfiguration = new btDefaultCollisionConfiguration();
	m_dispatcher = new	btCollisionDispatcher(m_collisionConfiguration);
     
#define maxProxies 8192
	btVector3 worldAabbMin(-10000,-10000,-10000);
	btVector3 worldAabbMax(10000,10000,10000);
	m_overlappingPairCache = new btAxisSweep3(worldAabbMin,worldAabbMax,maxProxies);

	btSequentialImpulseConstraintSolver* sol = new btSequentialImpulseConstraintSolver;
	m_solver = sol;

	m_dynamicsWorld = new btDiscreteDynamicsWorld(m_dispatcher,m_overlappingPairCache,m_solver,m_collisionConfiguration);

	m_dynamicsWorld->getDispatchInfo().m_enableSPU = true;
	m_dynamicsWorld->setGravity(btVector3(0,-10,0));

	//KINEMATIC GROUND
	btCollisionShape* groundShape = new btBoxShape(btVector3(btScalar(30.),btScalar(1.),btScalar(30.)));
	m_collisionShapes.push_back(groundShape);
	
	btTransform groundTransform;
	groundTransform.setIdentity();
	groundTransform.setOrigin(btVector3(0,-8,0));

	btRigidBody* body = localCreateRigidBody(btScalar(0.),groundTransform,groundShape);
	body->setCollisionFlags( body->getCollisionFlags() | btCollisionObject::CF_KINEMATIC_OBJECT);
	body->setActivationState(DISABLE_DEACTIVATION);
	body->setRestitution (btScalar(0.f));

	//create a few dynamic sphere rigidbodies (re-using the same sphere shape)
	btCollisionShape* colShape = new btSphereShape(btScalar(2.0));
	m_collisionShapes.push_back(colShape);
	
	/// Create Dynamic Objects
	btTransform startTransform;
	startTransform.setIdentity();
        btRigidBody* body2;

	...
		for (int k=0;k<ARRAY_SIZE_Y;k++)
		{
			for (int i=0;i<ARRAY_SIZE_X;i++)
			{
				for(int j = 0;j<ARRAY_SIZE_Z;j++)
				{
					startTransform.setOrigin(btVector3(
										2.0*i + start_x,
										2.0*k + start_y,
										2.0*j + start_z));

					body2 = localCreateRigidBody(1, startTransform,colShape);
					body2->setRestitution (btScalar(0.f));
				}
			}
		}
...
	clientResetScene();
}