Speed up convex-convex collisions.

PiperOrigin-RevId: 613450874
Change-Id: Ie66e0a078e2ff51a136b949dd9459847e1fe957d

doc/changelog.rst

@@ -2,6 +2,14 @@
 Changelog
 =========
 
+Upcoming version (not yet released)
+-----------------------------------
+
+MJX
+^^^
+
+1. Improved performance of SAT for convex collisions.
+
 Version 3.1.3 (March 5th, 2024)
 -----------------------------------
 

doc/mjx.rst

@@ -299,8 +299,8 @@ Collisions between large meshes
   SAT works well for smaller meshes but suffers in both runtime and memory for larger meshes.
 
   For
-  collisions between convex meshes and primitives (spheres, capsules, planes), use **3000 vertices or less** for your convex meshes.
-  For collisions between convex meshes and other convex meshes, use **30 vertices or less**.
+  collisions with convex meshes, the convex decompositon of the mesh should have
+  roughly **200 vertices or less** for reasonable performance.
   With careful
   tuning, MJX can simulate scenes with mesh collisions -- see the MJX
   `shadow hand <https://github.com/google-deepmind/mujoco/tree/main/mjx/mujoco/mjx/benchmark/model/shadow_hand>`__