Previously we used a 1D sequence to select a light, and another 2D sequence to sample a point on the light. For multiple lights this meant each light would get a random subset of a 2D stratified sequence, which is not guaranteed to be stratified anymore. Now we use only a 2D sequence, split into segments along the X axis, one for each light. The samples that fall within a segment then each are a stratified sequence, at least in the limit. So for example for two lights, we split up the unit square into two segments [0,0.5[ x [0,1[ and [0.5,1[ x [0,1[. This doesn't make much difference in most scenes, mainly helps if you have a few large area lights or some types of HDR backgrounds.
11 KiB
11 KiB