Even on high-end Linux systems, though, each frame of the animated movie took about 8 hours to render.
Much of that CPU time was consumed by ray tracing.
Ray tracing models lights path in a frame, so that it looks like youre seeing a real object lit up by the appropriate light sources. That doesnt sound too hard. Pixar has been doing that basic kind of thing since its early hopping lamp short films.
Whats new about Cars is the level of lighting and color detail that Pixar brought to its four-wheeled cast. Earlier films, such as The Incredibles, took only a fraction of the time to render even though they were produced with older technology.
To do this, Pixar used three of its own proprietary software packages, which run on Linux.
These are: Marionette, an animation software system for articulating, animating and lighting; Ringmaster, a production management software system for scheduling, coordinating and tracking a computer animation project; and RenderMan, a rendering software system for producing high-quality photorealistic images.
RenderMan, the most well-known of these programs, is also a standard interface for modeling programs and rendering programs capable of producing photorealistic quality images.