Thanks to a discovery by Petra Gospodnetic during her GSOC
project, I was able to substantially improve light tree sampling
for lambert surfaces. As part of this, the part of the surface
closure API relevant to light tree sampling has been adjusted to
be more flexible.
These improvements do not yet affect GTR surface light tree
sampling.
They are now generated by a build.rs script from nothing but the
colorspace's primaries, which makes it super easy to add more
colorspaces. So easy that I added three more: ACES AP0, ACES AP1
and Rec.2020.
This lays the foundation for supporting output to different
colorspaces.
If the average surface area of all the time samples is close enough
to the surface area of their union, just take the union and use that.
This both makes the BVH smaller in memory (time samples don't
propigate up the tree beyond their usefulness) and makes it
faster since traversal can avoid interpolating BBoxes when there's
only one BBox for a node.
The bug was in the previous commit, where I thought I was
preventing out-of-bounds access during traversal by limiting
the tree depth. While the idea was correct, I forgot that the
traversal stack needs _2_ extra slots on top of the tree depth,
not just 1. Fixed.
BVH traversal still happens in local space, but final actual
surface intersection calculations are done in world space by
transforming the triangle into world space. This is to improve
numerical consistency between intersections.
This, of course, depends on the simd ops being there, which
currently they are not. But in the future, hopefully this will
make things speedy. Will need to test, of course.
