Problem with triangle meshes and collision only

[chaosavy]

Hi, I'm using collision only aspect of Bullet, following the collision only demo to integrate Bullet with Ogre, I'm also using btOgre to convert my collision shapes from Ogre meshes to Bullet meshes. Everything works as expected when I use convex shapes, however when I switch to trimesh I no longer get collisions (any collisions).

Is there something I"m missing when using triangle shapes as opposed to using convex shapes?

Here is the code that I'm using:



Initializing bullet

Code: Select all

	btDefaultCollisionConfiguration* collisionConfiguration = new btDefaultCollisionConfiguration();
	btCollisionDispatcher* dispatcher = new btCollisionDispatcher(collisionConfiguration);
	btVector3	worldAabbMin(-20000,-20000,-20000);
	btVector3	worldAabbMax(20000,20000,20000);

	btAxisSweep3*	broadphase = new btAxisSweep3(worldAabbMin,worldAabbMax);

	collisionWorld = new btCollisionWorld(dispatcher,broadphase,collisionConfiguration);

Adding collision shape

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	BtOgre::StaticMeshToShapeConverter converter(entity);

	btBvhTriangleMeshShape* shapeTMP=converter.createTrimesh();

	btMatrix3x3 basisA;
	basisA.setIdentity();

	newBody.btColObj = new btCollisionObject;
	newBody.btColObj->getWorldTransform().setBasis(basisA);
	newBody.btColObj->setCollisionShape(shapeTMP);
	collisionWorld->addCollisionObject(newBody.btColObj);

	//Initial position
	newBody.btColObj->getWorldTransform().setOrigin(btVector3(newBody.prevPos.x, newBody.prevPos.y, newBody.prevPos.z));

Testing for collisions

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	if (collisionWorld)
		collisionWorld->performDiscreteCollisionDetection();


	int numManifolds = collisionWorld->getDispatcher()->getNumManifolds();
	int i;
	for (i=0;i<numManifolds;i++)
	{
		btPersistentManifold* contactManifold = collisionWorld->getDispatcher()->getManifoldByIndexInternal(i);
		btCollisionObject* obA = static_cast<btCollisionObject*>(contactManifold->getBody0());
		btCollisionObject* obB = static_cast<btCollisionObject*>(contactManifold->getBody1());

		Ogre::Entity *a=static_cast<Ogre::Entity*>(obA->getUserPointer());
		Ogre::Entity *b=static_cast<Ogre::Entity*>(obB->getUserPointer());

		int mover = findBody(a); //Need to get the previous position, entities and scene nodes
		int hit = findBody(b); //Need to get the previous position, entities and scene nodes

		//This gets collisions to be much closer
		/* Check all contacts points */
		int numContacts = contactManifold->getNumContacts();
		for (int j=0;j<numContacts;j++)
		{
			btManifoldPoint& pt = contactManifold->getContactPoint(j);

			if (pt.getDistance()<0.f)
			{
				collision(timeSinceLastFrame, mover, a, hit, b);
				break;
	      		}
		 }
	}

any ideas? thanks

[Mattg]

I don't think mesh vs. mesh collision is supported if that's what you're doing.

[chaosavy]

are you saying that triangle mesh to triangle mesh collision is not supported?

[Mattg]

Yes but I'm not sure. I know that triangle meshes aren't supported for dynamic bodies. Therefore there's no case where bullet need to do triangle mesh vs. triangle mesh collision which makes me think it's not supported/not implemented.

[chaosavy]

Looks like that's the deal, thanks for the help, I did some searching and found this

http://bulletphysics.org/Bullet/phpBB3/ ... ape#p15622

The issue I'm having is that I'm trying to create a carrier type space ship, that has an opening for fighter ships to land/pass through.

What I think I'll do is shoot a triangle detecting ray when I collide with these types of ships as a fighter ship to see if I should be going through the opening.