Contact Recycling

Contact recycling is a technique I developed for Box2D and Box3D. Contact recycling can drastically improve rigid body simulation performance, making the process of computing contact points almost free. Further, recycling can significantly improve stability.
Contact recycling combines ideas from other techniques. I had not seen this specific technique used in other physics engines as of March 2026 when I added it to Box2D in this pull request. There are similar solutions to the same problem but they have some fundamental differences.