The Linux engine in Cars

Jun. 21, 2006

Ever wonder how Lightning McQueen and friends looked so good in the movie Cars? A lot of that spit and polish came from the Pixar Animation Studio's Linux workstations and servers.

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 light's path in a frame, so that it looks like you're seeing a real object lit up by the appropriate light sources. That doesn't sound too hard. Pixar has been doing that basic kind of thing since its early hopping lamp short films.

What's new about Cars is the level of lighting and color detail that Pixar brought to its four-wheeled cast. Earlier films, such as the The Incredibles, took only a fraction of the time to render even though they were produced with older technology.

To do this, Pixar uses 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 of a computer animation project; and RenderMan, a rendering software system for producting high quality photo-realistic 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.

Thus, while Pixar has its own versions of RenderMan, there are other RenderMan-compliant renderers. Some of these, such as Pixie, are open-source. Almost all of them run on Linux.

Marionette, however, is all Pixar's and no one else's. It's used by Pixar for articulating, animating, and lighting its computer animations. Thus, it's the primary software tool for animators and technical directors at Pixar. Marionette, which runs on Linux, Solaris, and IRIX OS-powered workstations, has been designed and optimized for character articulation and animation.

Unfortunately, if you don't work at Pixar, you're not going to be able to use it. Or even see it in operation, for that matter, since Pixar is a closed studio.

Finally, Ringmaster is a production management and distributed rendering system for scheduling, coordinating and tracking animation projects. Ringmaster co-ordinates each frame's rendering on an array of Linux processors.

These clustered systems, which do nothing but render 24-hours a day, are known as a RenderFarm.

Open-source users will be disappointed to know that there are no signs that Pixar, now being bought out by Disney, will be open-sourcing any of its products.

Still, it is good to know that when the world's leading computer animation company needs to produce computer graphics, it turns to Linux for its operating system of choice.


-- Steven J. Vaughan-Nichols