27fc091be8
The original paper uses the single scattering albedo `sigma_s/sigma_t` to pick a channel for sampling the scattering distance. However, this only considers the situation where there is scattering inside the volume. If some channel has an extinction coefficient of zero, the light passes through without attenuation for that channel. We assign such channel with a weight of 1 instead of 0 to make sure it can be sampled. Pull Request: https://projects.blender.org/blender/blender/pulls/131741