Hi,
I'm having a problem with restitution when using small time steps. I've modified BasicDemo.cpp to demonstrate. I'm having problems actually uploading the file, but the important lines are below There's a static box (ground), and a sphere, each with a restitution coefficient of .98. So the sphere should be pretty bouncy, but it doesn't bounce at all. If I change the internal time step from 1/1000 to 1/60 (the default), there is some bounce, but for a restitution of .98 the bounce doesn't seem high enough to me. Am I misunderstanding something?
Thanks for the help!
Code:
m_dynamicsWorld->stepSimulation(ms / 1000000.f, 10000, 1/1000.);
This line seems to be causing the problem. If I change it to
Code:
m_dynamicsWorld->stepSimulation(ms / 1000000.f, 10000, 1/60.);
the ball bounces.
Code:
btCollisionShape* groundShape = new btBoxShape(btVector3(btScalar(50.),btScalar(50.),btScalar(50.)));
// btCollisionShape* groundShape = new btStaticPlaneShape(btVector3(0,1,0),50);
m_collisionShapes.push_back(groundShape);
btTransform groundTransform;
groundTransform.setIdentity();
groundTransform.setOrigin(btVector3(0,-50,0));
//We can also use DemoApplication::localCreateRigidBody, but for clarity it is provided here:
{
btScalar mass(0.);
//rigidbody is dynamic if and only if mass is non zero, otherwise static
bool isDynamic = (mass != 0.f);
btVector3 localInertia(0,0,0);
if (isDynamic)
groundShape->calculateLocalInertia(mass,localInertia);
//using motionstate is recommended, it provides interpolation capabilities, and only synchronizes 'active' objects
btDefaultMotionState* myMotionState = new btDefaultMotionState(groundTransform);
btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,groundShape,localInertia);
btRigidBody* body = new btRigidBody(rbInfo);
body->setRestitution(.98);
//add the body to the dynamics world
m_dynamicsWorld->addRigidBody(body);
}
{
//create a few dynamic rigidbodies
// Re-using the same collision is better for memory usage and performance
btCollisionShape* colShape = new btSphereShape(5);
//btCollisionShape* colShape = new btSphereShape(btScalar(1.));
m_collisionShapes.push_back(colShape);
/// Create Dynamic Objects
btTransform startTransform;
startTransform.setIdentity();
btScalar mass(1.f);
//rigidbody is dynamic if and only if mass is non zero, otherwise static
bool isDynamic = (mass != 0.f);
btVector3 localInertia(0,0,0);
if (isDynamic)
colShape->calculateLocalInertia(mass,localInertia);
startTransform.setOrigin(btVector3(5,20,5));
//using motionstate is recommended, it provides interpolation capabilities, and only synchronizes 'active' objects
btDefaultMotionState* myMotionState = new btDefaultMotionState(startTransform);
btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,colShape,localInertia);
btRigidBody* body = new btRigidBody(rbInfo);
body->setRestitution(.98);
m_dynamicsWorld->addRigidBody(body);
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