By a completely random event I found out during the same day about Metropolis light system, that old blender patch and a really nice paper “Specular Manifold Sampling for Rendering High-Frequency Caustics and Glints”.
As far as I can understand it, it’s a faster system that can be integrated into a classical unidirectional path tracer (like cycle) and work in team with the “default” system. It can help to generate caustic more quickly, help with Glints and seem well suited for an integration with the branched path tracer. Doing so, we could use a settings to specify how many bounces to use for SMS (0 = disable, 1 = only one refraction/reflection, etc…).
It seem that this solution is way better than the work on T38401 because it doesn’t require a long pre-computation step and can be integrated without being a separate integrator.
I know, it’s probably a huge task to do it right but I’m willing to help. I just got too excited and lost in the source code of Blender (and cycle). The source code is available for their algorithm and I already looked the “Multi-scattering caustic SMS”, “Glint SMS” and the combined path tracer. But my knowledge of the internal mechanism of cycle is the main turn down that keep me from trying to port a working system for now.
And, because this task is not as simple as adding just a magic button, I prefer to get cycle’s developers advises and comment before. It may be something that isn’t interesting (in that current form) for cycle. Do you thing it can be interesting ? Can be done ? What should I consider if you give me a positive feedback ?