Gotta Have Shaders

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Rudy Poat's CG short, Fruits of Labor, which screened at thisyear's Siggraph Electronic Theater, has received attention forcombining radiosity rendering techniques with extended shading modelsto produce near-photo-real surfaces. Poat, who is currently digitalcreative director at San Francisco's Wild Brain, wrote and directed thefilm in collaboration with Atlanta-based Giant Studios after previouslyworking as CG color and lighting supervisor on The Matrix. Now,Poat and Giant are extending the Fruits story and advancing theradiosity/shading approach with a new 20-minute film.

The original film detailed the fate of a stick-like man who gets hishead stuck inside an apple on a picnic table. The new film will followthe little guy as he embarks on a quest through a dark labyrinth world,guided by strange, recurring dreams.

Poat hopes the extended film will interest the animation communitybecause of its attempt to create “photo-real, visualfeasts” by combining volumetric shader systems and radiositywork. Poat uses Softimage XSI as a foundational lighting tool becauseits built-in, interactive rendering feature allows animators to drawregion boxes around objects, build render trees, and achieve fastrenders of specific areas. Poat says the approach essentially uses XSI“as a front-end shader lighting tool” for outputrendering.

“The first film was an in-house test at Giant to prove thatthis specific shading system we developed would work withradiosity,” Poat explains. “The concept of adding layers,using volumetric shading techniques, to surfaces lit with radiosity isfairly new, and we wanted to prove the concept. The idea is to use thesame techniques you would use with real-world lighting, so onFruits, we used bounce cards to let the software calculate anddistribute all those light bounces, which meant writing a lot of code.Now, with the new film, we hope to go even further.”

Poat's team is doing that by liberally mixing rendering toolsthrough the XSI interface.

“We can use RenderMan and Mental Ray together, all throughXSI,” says Poat. “We are writing code to use them in XSI ina way that is transparent to the user. That will permit animators touse the best parts of multiple rendering tools to build volumetricshaders that react seamlessly with radiosity. That way, we can buildmore layers into the surfaces. With this approach, volumetric shaderscan now become practical for radiosity scenes, where we might ray-marchthrough a single surface 30 times for realistic results, adding all thecorrect sub-surface scatter and outer microscopic grime anddust.”


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