Abstract: 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. Movie-quality 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'.

One-line summary: Overview of ray tracing in PRMan, and the use of ray tracing in 'Cars'.

Published in: Proceedings of the IEEE Symposium on Interactive Ray Tracing 2006, pages 1-6. IEEE, September 2006. (Salt Lake City, USA, September 18-20.)

Download paper here: paper.pdf.

More information about the technology used for 'Cars' can be found in e.g. these SIGGRAPH 2006 presentations:

• Tim Milliron and Gary Schultz. Special Session: "Vroom Vroom: SIGGRAPH at 500 Horsepower".
• Ferdi Scheepers and Andy Whittock. "The wrecked road in 'Cars,' or How to damage perfectly good geometry".
• Erik Smitt. "One thousand lights at 200 mph".

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