LJ Interviews Larry Gritz

Amy Wood, the graphics/layout artist for Linux Journal interviewed Larry Gritz of Pixar Animation Studios on August 16.

AmyI understand that you were a Technical Director for the latest great animation feature film, Toy Story. Can you tell us what you did in that role?

LarryI was one of 30 or so technical directors (TDs) who worked on that film. TD is the job title for people who create the models, write shaders and light the shots. Essentially, they are technical folks responsible for the visual look of the film. Another group, the animators—typically with classical animation rather than technical backgrounds—is responsible for the motion or acting of the characters. There are also countless other people writing the story, designing the look, painting, developing software and so on. In all, it's quite a big team of incredibly talented people. I came into the project fairly late in the production, after modeling was mostly done, but I got to work on shaders and lighting.

What is your background? How did you get involved with graphics?

I started out interested mainly in compilers, but I took a course in computer graphics when I was an undergraduate at Cornell, and I've been hooked ever since. I started tinkering around with writing renderers, and concentrated on graphics in graduate school at George Washington University, doing my MS thesis about a new way of calculating a particular kind of light propagation. I stayed for a PhD (which I am still in the process of wrapping up), doing more research in animation techniques, among other things.

Can you tell us about your Blue Moon Rendering Tools software?

BMRT is a high quality renderer which supports ray tracing and radiosity, area lights, volumetric effects and other advanced features. It runs on several Unix platforms, including SGI, Sun, HP, NEXTSTEP, and of course, Linux. It's cheap shareware, and is free for academic and non-commercial usage. Features that set it apart from most other renderers include support of curved high level surfaces such as bicubic patches and trimmed NURBS, good anti-aliasing support and programmable shading (users can write little programs called “shaders” which control the appearances of surfaces and lights). These features aren't found in many renderers (including big commercial packages), but they are essential to high-end, professional quality rendering.

BMRT is fully compliant with the RenderMan Interface Specification, developed by Pixar. RenderMan is a standard way for modelers to talk to renderers, sort of like PostScript, but for describing 3-D photo-realistic scenes. By being RenderMan compliant, BMRT is largely compatible with Pixar's PhotoRealistic RenderMan product (PRMan, for short), which is probably the most commonly used renderer for feature film effects work (and of course, was used to render Toy Story).

BMRT is not particularly easy to use; it's really more of a developer's product. But it's extremely powerful—much more so than any of the other free renderers out on the net, which are more oriented toward hobbyists.

The BMRT home page, www.seas.gwu.edu/student/gritz/bmrt.html, has several pictures that have been rendered using my software.

Why did you pick Linux as a platform for Blue Moon?

A couple of years ago, I was introduced to Linux by Youngser Park, a fellow graduate student at GWU. He asked me to port BMRT to Linux so that he and other students could run the renderer (as well as our other lab tools) at home. I remember the first time I was at his place and saw Linux running on his computer. I'd heard of Linux before, but never imagined that it could be a robust implementation. When I saw X11 running and realized how easy it was to set up an environment just like I was used to on the SGI, I knew I needed to be running it on my home machine, as well.

What are some interesting projects where the BMRT have been/are used? Is BMRT a popular package? Do you know of any studios that use it running under Linux?

BMRT is fairly popular in the high end. It's rather hard for beginners to use, so it doesn't come close to say, POV-Ray, in terms of the number of people who use it. But because it's so powerful, and RenderMan compliant, it's gotten noticed by a lot of production houses. Judging by the mail I receive, several well-known studios have at least tried it out. Pixar's renderer is much faster, and is less prone to some very subtle artifacts, so no studios would want to use my software instead of PRMan. But since the algorithms are very different, many houses use them together—PRMan for the bulk of the work, and BMRT for those pesky scenes when they just have to have ray tracing or area lights or something. I can't name the studios, but I know BMRT has been used for a couple TV commercials and for an episode of Star Trek: Voyager. I don't think it's been used for final frames of any feature films yet, but I wouldn't be surprised if that happened soon.

I don't know any studios currently using Linux “officially”, but many people who work at production houses run Linux at home and like to be able to continue to tinker with shaders and such.

How do you think Linux compares to other platforms?

I think it's a more robust Unix-like OS than many I've seen from the big commercial workstation vendors. I also like the spirit of community and the kind of high-quality, low cost software that is available for Linux. I've tried to contribute to that with the availability of my software for Linux.

Do you think your decision to offer a commercial graphical/rendering tool for Linux will inspire others to make more packages available?

I hope so. With high end Intel chips being a very cost-effective way to get lots of computational power, I wouldn't be surprised to see studios using large farms of Intel-based hardware for their rendering or other graphics tasks. If this is the case, I'd much rather see these machines running Linux than NT.

And in the vein of Barbara Walters, if you had to be one character in Toy Story, who would you be?

Probably Sid, though perhaps without the sadistic streak. I like the tinkerer in him. He has sort of a God complex, but he sure does make interesting toys.

Note that RenderMan is a registered trademark of Pixar, and Toy Story is registered and copyrighted by Walt Disney Corporation. The RenderMan Companion by Steve Upstill (Addison-Wesley, 1990) is a good reference for more information about the RenderMan standard.