For distribution ray tracing in production scenes, the bottleneck is the time spent evaluating complex shaders at the ray hit points. We speed up this shader evaluation time for global illumination by separating out the view-independent component and caching its result --- the radiosity. Our cache contains three resolutions of the radiosity; the resolution used for a given ray is selected using the ray's differential. The resulting single-pass global illumination method is fast and flexible enough to be used in movie production, both for interactive lighting design and final rendering. It is currently being used in production at several studios.
The multiresolution cache is also used to store shader opacity
results for faster ray-traced shadows, ambient occlusion and volume
extinction, and to store irradiance for efficient ray-traced
Additional materials: [siggraphtalk.pdf], [subsurf.m4v], [globillum.m4v], [siggraphslides.pdf]
Available as Pixar Technical Memo #12-06