triangles instead of boxes in Glue/Fracture "basicDemo" code

[tramblin]

when using the "basicDemo" code at the bottom of this link:

http://code.google.com/p/bullet/issues/detail?id=90

if i replace the box shapes with this code below, (using triangles instead of box shapes) and i put it in Fracture mode. then fire off spheres at the triangles, the triangles break away naturally,
but when they fall to the two platforms i've set up, (for experimentation) one with mass one with no mass..
most of the Triangles pass right through the Box shape platforms like they were not there. what am i doing wrong in the code below?

(several of the extra settings (set away from default) are just experiments to see if i could improve on the triangle/platform dynamics)

see screen shot in file attachment...

(also many times the spheres will pass right through the triangles about 10% of the time)

Code: Select all

#define ARRAY_SIZE_X 10
#define ARRAY_SIZE_Y 10
#define ARRAY_SIZE_Z 3

#define SCALING 1.
#define START_POS_X -5
#define START_POS_Y 1
#define START_POS_Z 10


       btBoxShape *theGround2 = new btBoxShape(btVector3(btScalar(18.),btScalar(1.),btScalar(10.))); 
	theGround2->setMargin(0.004f);
	btCollisionShape* groundShape2 = theGround2;

	m_collisionShapes.push_back(groundShape2);

	{
		btTransform groundTransform;
		groundTransform.setIdentity();
		groundTransform.setOrigin(btVector3(0,-3,10));

		btScalar mass(0.0f);

		bool isDynamic = (mass != 0.f);
		btVector3 localInertia(0,0,0);
		if (isDynamic) groundShape2->calculateLocalInertia(mass,localInertia);

		btDefaultMotionState* myMotionState = new btDefaultMotionState(groundTransform);
		btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,groundShape2,localInertia);
		btRigidBody* body = new btRigidBody(rbInfo);

		m_dynamicsWorld->addRigidBody(body);
	}

	btBoxShape *theGround = new btBoxShape(btVector3(btScalar(15.),btScalar(1.),btScalar(7.))); 
	theGround->setMargin(0.04f);
	btCollisionShape* groundShape = theGround;

	m_collisionShapes.push_back(groundShape);

	btTransform groundTransform;
	groundTransform.setIdentity();
	groundTransform.setOrigin(btVector3(0,-1,10));

	{
		btScalar mass(3.5f);

		bool isDynamic = (mass != 0.f);
		btVector3 localInertia(0,0,0);
		if (isDynamic) groundShape->calculateLocalInertia(mass,localInertia);

		btDefaultMotionState* myMotionState = new btDefaultMotionState(groundTransform);
		btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,groundShape,localInertia);
		btRigidBody* body = new btRigidBody(rbInfo);

		m_dynamicsWorld->addRigidBody(body);
	}


	{
		btVector3 p1(-0.70f,-0.55f, 0);
		btVector3 p2( 1.30f,-0.55f, 0);
		btVector3 p3(-0.70f, 1.45f, 0);

		btTriangleShape *theTriangle = new btTriangleShape(p1,p2,p3); 

		theTriangle->setMargin(0.04f);

		btCollisionShape* colShape = theTriangle;

		m_collisionShapes.push_back(colShape);

		btTransform startTransform;
		startTransform.setIdentity();

		btScalar	mass(0.1f);

		bool isDynamic = (mass != 0.f);
		btVector3 localInertia(0,0,0);
		if (isDynamic) colShape->calculateLocalInertia(mass,localInertia);

		float start_x = START_POS_X - ARRAY_SIZE_X/2;
		float start_y = START_POS_Y;
		float start_z = START_POS_Z - ARRAY_SIZE_Z/2;

		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(SCALING*btVector3(
											btScalar(2.0*i + start_x),
											btScalar(2.0*k + start_y),
											btScalar(2.0*j + start_z)));

						btDefaultMotionState* myMotionState = new btDefaultMotionState(startTransform);
						btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,colShape,localInertia);
						btFractureBody* body = new btFractureBody(rbInfo, m_dynamicsWorld);

						sFractureBodies.push_back(body);

						btTransform tr;
						tr.setIdentity();
						btQuaternion orn(btVector3(1,0,0),45);
						tr.setRotation(orn);


						body->setWorldTransform(tr);
						
						body->setActivationState(ISLAND_SLEEPING);
						m_dynamicsWorld->addRigidBody(body);
						body->setActivationState(ISLAND_SLEEPING);

				}
			}
		}

[Erwin Coumans]

You should never use btTriangleShape, it is only for internal use for btBvhTriangleMeshShape.

For fracture, it is best to either use primitives or convex hull (btConvexHullShape) with volume.
Thanks,
Erwin

[tramblin]

is it because they have no volume? I'm going to look at ConvexHullShape, but I thought that this would not fracture with the basicDemo code into triangles? i will look to see how to fit hull shape in the code above to see if it will fracture to shards or individual triangles.. that seems like it would be back to the same problem but maybe not.

the idea/code above works rather well (ie looks rather natural as it breaks apart), i want to shatter into shards, triangles, like glass. but they float through the platform when they fall.