[33a]

Posted a reply here https://news.ycombinator.com/item?id=40466855

This is a specific reference on how constraints model contact between rigid bodies https://box2d.org/files/ErinCatto_UnderstandingConstraints_G...

Most games since Half Life 2 use constraint forces like this to solve collisions. Springs/penalty forces are still used sometimes in commercial physics solvers since they're easier to couple with other simulations, but they require many small timesteps to ensure convergence.