ABSTRACT Ray Tracing for the Movie ‘Cars’

This paper describes how we extended Pixar’s RenderMan renderer with ray tracing abilities. In order to ray trace highly complex scenes we use multiresolution geometry and texture caches, and use ray differentials to determine the appropriate resolution. With this method we are able to efficiently ray trace scenes with much more geometry and texture data than there is main memory. Moviequality rendering of scenes of such complexity had only previously been possible with pure scanline rendering algorithms. Adding ray tracing to the renderer enables many additional effects such as accurate reflections, detailed shadows, and ambient occlusion. The ray tracing functionality has been used in many recent movies, including Pixar’s latest movie ‘Cars’. This paper also describes some of the practical ray tracing issues from the production of ‘Cars’.

An Irradiance Atlas for Global Illumination in Complex Production Scenes

We introduce a tiled 3D MIP map representation of global illumination data. The representation is an adaptive, sparse octree with a “brick ” at each octree node; each brick consists of 8 3 voxels with sparse irradiance values. The representation is designed to enable efficient caching. Combined with photon tracing and recent advances in distribution ray tracing of very complex scenes, the result is a method for efficient and flexible computation of global illumination in very complex scenes. The method can handle scenes with many more textures, geometry, and photons than could fit in memory. We show an example of a CG movie scene that has been retrofitted with global illumination shading using our method. 1

Ray differentials and multiresolution geometry caching for distribution ray tracing in complex scenes

When rendering only directly visible objects, ray tracing a few levels of specular reflection from large, lowcurvature surfaces, and ray tracing shadows from point-like light sources, the accessed geometry is coherent and a geometry cache performs well. But in many other cases, the accessed geometry is incoherent and a standard geometry cache performs poorly: ray tracing of specular reflection from highly curved surfaces, tracing rays that are many reflection levels deep, and distribution ray tracing for wide glossy reflection, global illumination, wide soft shadows, and ambient occlusion. Fortunately, less geometric accuracy is necessary in the incoherent cases. This observation can be formalized by looking at the ray differentials for different types of scattering: coherent rays have small differentials, while incoherent rays have large differentials. We utilize this observation to obtain efficient multiresolution caching of geometry and textures (including displacement maps) for classic and distribution ray tracing in complex scenes. We use an existing multiresolution caching scheme (originally developed for scanline rendering) for textures and displacement maps, and introduce a multiresolution geometry caching scheme for tessellated surfaces. The multiresolution geometry caching scheme makes it possible to efficiently render scenes that, if fully tessellated, would use 100 times more memory than the geometry cache size. 1