Computer Graphics World

June 2009 15 Character Modeling•Animation n n n n and who was art supervisor for such films as e ree Caballeros and Saludos Amigos, set in South America. ey also looked at George Booth cartoons, and Hank Ket- chum's "Dennis the Menace." To create storybook backgrounds, the artists used simple shapes for bushes in the jungle, eliminating any leaf that didn't face the camera, and stylized the shading and modeling for Carl's house. "We wanted Carl's house to feel small, like a dollhouse," notes Steve May, supervising technical di- rector, "as if big hands made small pieces and placed them by hand." e trim around the fireplace doesn't quite line up. e fireplace has soot, but if you look closely, you see that the soot is ac- tually brush strokes made with a dry brush, as are the bark on the trees and the dirt on Russell's face. "You'll see this style everywhere in the movie," May says. "We used a variety of procedural and paint components in the shaders, but generally we had a painted brush stroke in a paint pass with every shader." In addition to Carl, Ellie, Russell, and Charles Muntz, the main characters include a 13-foot-tall bird that emerges from the jungle after the balloon-driven house lands on a tabletop mountain in Venezuela. Rus- sell names the bird Kevin, but the dog that also pops out from the brilliant jungle names himself: Dug wears a collar that translates his thoughts into words. Sud- denly, Carl now has two "family members" circling him. Kevin is colorful and silly, with a round body and long neck, and Dug is an enthusiastic, overweight golden retriever/lab mix that loves everyone. Carl's a tough old cookie. It takes more than one "buddy" to bring him back to life. For the characters, modelers working in Autodesk's Maya adopted a "less is more" philosophy. Carl is three heads tall with stocky arms and legs. Russell is a little egg. Dug has a big, round nose. "We removed anything extra," May says. e characters don't have ear holes or nostrils, for exam- ple, not even Dug. It was character supervisor omas Jor- dan's team of approximately 30 people who had first turned the concept art, maquettes, and expression sculpts for characters into 3D models that could move and that met the design goals. Each of the main charac- ters had its own unique problems to solve. "It was more of a challenge than usual to finalize these characters," Jordan says. "No one can tell you what simplexity means. We had to find it. e sketches and maquettes didn't work in 3D once we started animat- ing them." Animators gave the riggers drawings of expressions they wanted to hit, and the riggers, working in Pixar's proprietary soft- Carl and Russell travel in Carl's balloon-powered house through skies filled with clouds in approximately 150 shots—fluffy, white clouds and dark, stormy clouds. The clouds are volumetric, constructed from spheres using a system developed by TD Alexis Angelidis. In the entire film, 400,000 different spheres create the clouds; the storm alone uses 85,000. "Alexis can place a sphere, maybe even as large as a football field," explains Gary Bruins, effects supervisor, "and then run a script that breaks it into a fractal distribution of spheres with different radiuses. The scripts helped with general modeling, but Alexis built the clouds by mostly adding sphere onto sphere." The various-sized large spheres described the overall cloud shape; the smaller spheres added detail. Each cloud model had two shader versions, one for the surface and another for the interior. The interior allowed object matting—the house, for instance—but no camera motion blur. The surface supported camera motion blur but didn't allow embedded objects. "We had a switch that we could flip on a per-shot basis," Bruins says. To scatter light within the clouds, TD John Pottebaum created a 3D density map. "In addition to lighting artists using their tools and John's 3D density map, Alexis replicated, in the shader, the lighting response of water droplets in the cloud," Bruins explains. "And, his volumetric caching system was a huge help in optimizing rendering." –Barbara Robertson

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