Mesh-Mesh collision (get triangle indices)

[kvasnevskyivlad]

Hi, I recently started experimenting with a bepuphysics2, and what I really need it to be able to do is detect collisions between two meshes. Also, my meshes might be concave (not convex). Is it possible at all? And I need to be able to detect the indices of collidable triangles on both meshes if there is a collision. Can you help me with it? Thanks in advance!

[RossNordby]

You can, but:

1. The API remains a bit annoying in this space, mostly because it assumes batched execution over multiple pairs.
2. Mesh-mesh collisions are much slower than they could be. They're way below the standard of the rest of the library because it's a rare and historically deprioritized use case. It's still typically fast enough for what it sounds like you might need, it could just be much faster.
3. Triangles are one sided and will not generate contacts whose collision normals would be associated with the triangle's backface. This can sometimes produce surprising results.

That said, check out the CollisionQueryDemo for an example that's adjacent. Notice the OnChildPairCompleted callback in the ICollisionCallbacks implementation; it'll report individual convex subpair test results. The childA and childB would be the indices of triangles if the shapes involved in the top-level test were meshes.

That demo is a little more complex than just testing two meshes against each other because it's querying the simulation with Simulation.BroadPhase.GetOverlaps(queryBoundsMin, queryBoundsMax, ref broadPhaseEnumerator). In your case, it sounds like you already know the shapes you want to test.