Box2D dev unveils contact recycling, making contact generation almost free in physics sims
EricLengyel · x · 2026-10-14
Erin Catto, author of Box2D/Box3D, published a write-up on Contact Recycling, a technique he developed that drastically improves rigid body simulation performance, making contact point computation almost free while improving stability.
- Motivation: in large stacks of bodies, stationary parts shouldn't have contact points recomputed every timestep — contact generation is one of the costliest stages; relatively-static pairs (a box on a moving train) should also be recycled.
- Approach: reuse contact points from the previous timestep, combining ideas from related techniques; as of March 2026 he hadn't seen this specific variant in other engines.
- The article includes background on contact manifolds and shipped in a Box2D PR merged in March 2026.
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