bullet-featherstone: Use a single contact manifold for each convex decomposed mesh collision

[iche033]

🦟 Bug fix

Summary

Contact point optimization for convex decomposed mesh collisions in bullet-featherstone plugin. This PR reduces the number of contact points generated for convex decomposed mesh collision by using a single contact manifold.

Previously when a mesh collision is decomposed into multiple convex hull shape, each convex hull shape has a corresponding contact manifold which can generate up to 4 contact points (4 is the default limit in bullet). This slows down sim especially when querying contact points (via GetContactsFromLastStep). This PR overrides the btCollisionDispatcher class in order to update the contact manifolds stored in bullet. It post processes the contact points, generates a single contact manifold for each collision associated with convex hull shapes, and clears the exiting contact manifolds.

Note: it would be more efficient if we can do this inside bullet to avoid generating all the contact manifolds in the first place.

Before: many points can be generated from one convex decomposed mesh collision.

After: limit contact points to <= 4

Here're remotery graphs showing before and after the fix for a scene with multiple convex decomposed meshes. Note objects were auto-deactivated when these graphs were captured.

Before: >200 contact points

After: 20 contact points

Notable speedups are:

• PhysicsPrivate::Step: 0.153ms -> 0.097ms
• PhysicsPrivate::UpdateCollision: 0.528ms -> 0.135ms

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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[azeey]

Looks like there are several test failures in windows and I don't see any in the stable branch (https://build.osrfoundation.org/view/gz-harmonic/job/gz_physics-7-win/)

[iche033]

Looks like there are several test failures in windows and I don't see any in the stable branch (https://build.osrfoundation.org/view/gz-harmonic/job/gz_physics-7-win/)

Fixed and this PR is ready for review again. The test failures were due to RTTI access violation when doing a dynamic_cast from btCollisionShape to btCompoundShape. I saw a similar issue reported in dartsim and fixed by adding pragmas in base classes but that's not viable here so I switched to static_cast.