Blender Git Loki

Improved triangle sampling for mesh lights

This implements Arvo's "Stratified sampling of spherical triangles". Similar to how we sample rectangular area lights, this is sampling triangles over their solid angle. It does significantly improve sampling close to the triangle, but doesn't do much for more distant triangles. So I added a simple heuristic to switch between the two methods. Unfortunately, I expect this to add render time in any case, even when it does not make any difference whatsoever. It'll take some benchmarking with various scenes and hardware to estimate how severe the impact is and if it is worth the change.

Reviewers: #cycles, brecht

Reviewed By: #cycles, brecht

Subscribers: Vega-core, brecht, SteffenD

Tags: #cycles

Differential Revision: https://developer.blender.org/D2730