Introduction: We describe a multiresolution radiosity caching method that enables efficient computation of global illumination (GI) in a single pass in complex CG movie production scenes. For ray-traced GI in scenes with complex geometry and shaders, the bottleneck is not the ``raw'' ray tracing (acceleration structure traversal and ray hit tests), but the evaluation of displacement, light source, and surface shaders at the ray hit points. We reduce this time by dividing the shader calculations into view-dependent and view-independent components, and caching the view-independent part (radiosity) needed for GI. During distribution ray tracing these radiosities are computed on demand and reused many times. The cache contains multiple resolutions of the radiosity on the surface patches in the scene; the resolution for each cache lookup is selected using ray differentials. Our GI method is implemented in PRMan and used for interactive material/lighting design and final rendering at several studios.

One-line summary: Radiosity caching speeds up distribution ray traced global illumination by more than 30 times in production shots.

Published in: SIGGRAPH 2012 Talks. ACM, August 2012. (Los Angeles, USA, August 5-9.)

Download the talk extended abstract and slides: talk and slides (look under supplemental material).

More information (and videos) in: Pixar Technical Memo #12-06.

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