a466d7ae24
Previously we picked one of the RGB channels with equal probability, but this works poorly in a dense volume after many bounces. Now we take into account the throughput and single scattering albedo. This makes it a little more practical to do brute force SSS with volumes, but is still very inefficient because we do direct light sampling at every volume bounce even when inside an opaque mesh. In theory there could be a light inside the mesh so we can't automatically disable direct lighting.