The first step generates a point cloud (surfel) representation of the directly illuminated geometry in the scene. The surfels in the point cloud are organized in an octree, and the power from the surfels in each octree node is approximated either as a single large surfel or using spherical harmonics. To compute the indirect illumination at a receiving point, we rasterize the light from all surfels using three degrees of accuracy: ray tracing, disk approximation, and clusters. Huge point clouds are handled by reading the octree nodes and surfels on demand and caching them.
The method is integrated into Pixar's RenderMan renderer (PRMan) and
has been used in the production of more than 35 feature films to date.
Additional materials: [Slides.pdf]