Chaos cloth simulations with temporal AA render incorrectly. It seems like the simulation resets the seed with each subsample. As a consequence in rendered material the cloth is twitching and not behaving naturally.
The only method to make it work is caching the chaos sim
Steps to Reproduce
Render the simulated cloth with standard deferred rendering as a reference, then render the same sequence adding antialiasing to render settings, and setting temporal samples to 16 and spatial samples to 1, and AA override set to none.
When using temporal samples, the simulation is sub-stepped to the number of sub-samples.
This is the equivalent of running the same simulation with the number of solver substeps mulitplied by 16.
This has the side effect of reducing the size of the simulation timesteps and of causing a greater convergence. Greater convergence means the spring constraints get tighter and any overconstraint in your setup will appear like twitching.
The solution in this case is to rework the solver and constraint parameters for this asset so that the simulation behaves correctly with the reduced timestep.
You can start by reducing the number of iterations and substeps, then if it is not enough, you might have to readjust and lower the stiffness of all your constraints (stretch, bending, long range attachment, … etc.).
Thanks Kriss,
That’s a helpful insights!
Let me look into that and get back to you