Nice. I played with a similar thing years ago: rigid bodies connected with various constraints. The simple solving for the acceleration of the point masses under the forces from the connections that this computation seems to do works fine as long as the cloth is elastic. If you try to compute the dynamics of points connected by rigid rods, the large forces makes the system really stiff and your integration time step drops precipitously. In that case you have to generate a large linear system of equations and solve for the global motion of the system. It's quite a bit trickier. It's also interesting how situations that are familiar from real life, like a drawer getting stuck diagonally in the slot, really are singularities in the equations.<p>I realized this was actually an area of research, and found a bunch of papers by this guy: <a href="http://www.cs.cmu.edu/~baraff/pbm/pbm.html" rel="nofollow">http://www.cs.cmu.edu/~baraff/pbm/pbm.html</a>