Collisions with btGImpactMeshShape objects

[karnivaurus]

I want to create two rigid objects, each described by a triangle mesh. One is a static plane, and the other is a dynamic cube which falls under gravity. What I want to happen is for the cube to hit the plane and then rest on the plane. However, in my implementation, the cube just passes straight through the plane and continues to fall the other side.

I have visualised this and the cube and the plane definitely collide, so it is not an issue with the vertex coordinates. I have used btGImpactMeshShape for the shape of both the plane and the cube, and then btDefaultCollisionConfiguration to detect collisions. Are these two compatible?

I know that I can make a plane using something much more simple than a triangle mesh, but this is just a toy example, simplified from something more complex I am trying to make.

Below is my code for setting up Bullet and creating the two objects. After stepping through the simulation of the dynamics world, I get the behaviour describe above where the cube passes right through the plane.

Any help? Thank you!

Code: Select all

    // Set up Bullet
    btDefaultCollisionConfiguration* collision_configuration = new btDefaultCollisionConfiguration();
    btCollisionDispatcher* dispatcher = new btCollisionDispatcher(collision_configuration);
    btBroadphaseInterface* broadphase = new btDbvtBroadphase();
    btSequentialImpulseConstraintSolver* solver = new btSequentialImpulseConstraintSolver;
    dynamics_world = new btDiscreteDynamicsWorld(dispatcher, broadphase, solver, collision_configuration);
    dynamics_world->setGravity(btVector3(0, -9.81, 0));

    // Make the Plane
    btTriangleIndexVertexArray* plane_mesh = MakePlaneMesh(); // My own function to create a thin plane mesh
    btGImpactMeshShape* plane_shape = new btGImpactMeshShape(plane_mesh);
    plane_shape->setLocalScaling(btVector3(1., 1., 1.));
    plane_shape->setMargin(0.04f);
    plane_shape->updateBound();
    btVector3 plane_inertia(0,0,0);
    btScalar plane_mass(0.0f); // Zero mass so that the plane is static
    plane_shape->calculateLocalInertia(plane_mass, plane_inertia);
    btTransform plane_start_transform;
    plane_start_transform.setFromOpenGLMatrix(GetPlanePose()); // GetPlanePose() is my own function to get the pose of the plane, which is set to be below the cube
    btDefaultMotionState* plane_start_motion_state = new btDefaultMotionState(plane_start_transform);
    btRigidBody* plane = new btRigidBody(plane_mass, plane_start_motion_state, plane_shape, plane_inertia);
    plane->setFriction(0.5);
    plane->setRestitution(0.5);
    dynamics_world->addRigidBody(plane);

    // Make the Cube
    btTriangleIndexVertexArray* cube_mesh = MakeCubeMesh(); // My own function to create a cube mesh
    btGImpactMeshShape* cube_shape = new btGImpactMeshShape(cube_mesh);
    cube_shape->setLocalScaling(btVector3(1., 1., 1.));
    cube_shape->setMargin(0.04f);
    cube_shape->updateBound();
    btVector3 cube_inertia(0,0,0);
    btScalar cube_mass(1.0f);
    cube_shape->calculateLocalInertia(cube_mass, cube_inertia);
    btTransform cube_start_transform;
    cube_start_transform.setFromOpenGLMatrix(GetCubePose()); // GetCubePose() is my own function to get the pose of the cube, which is set to be above the plane
    btDefaultMotionState* cube_start_motion_state = new btDefaultMotionState(cube_start_transform);
    btRigidBody* cube = new btRigidBody(cube_mass, cube_start_motion_state, cube_shape, cube_inertia);
    cube->setFriction(0.5);
    cube->setRestitution(0.5);
    dynamics_world->addRigidBody(cube);