Using bullet for overlapping bodies, begin/end_collision

[Phillemann]

Hi

I'd like to use bullet not for collision response but only for collision detection, but with moving bodies. How do I do that? In particular, it would be nice if I could receive callbacks only for "begin collision" and "end collision" not each time a body pair overlaps.

[Erwin Coumans]

It is not clear what you mean by 'begin collision' and 'end collision'.

Bullet can report when contact points are added, updated and removed. For all of those there are contact callbacks:

ContactAddedCallback gContactAddedCallback;
ContactDestroyedCallback gContactDestroyedCallback;
ContactProcessedCallback gContactProcessedCallback;

Just assign the callback, and flag objects that require a callback:

Code: Select all

body->setCollisionFlags(body->getCollisionFlags() | btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK);

See attached BasicDemo for example usage.

In general, it is better to iterate over the overlapping pairs, and just check the number of contacts the the contact manifold. See Bullet/Demos/CollisionInterfaceDemo.
Hope this helps,
Erwin