Computer Graphics World

January 2009 22 n n n n CG I details on the textures but retain the color palette." For this, the artists used Adobe's Photoshop and Maxon's BodyPaint 3D. Once completed, the textures moved through Maya into Pixar's RenderMan. e challenge was in the quantity: e artists needed to surface 40,000-plus unique assets, including props and charac- ters. "Everything in our sets was modeled," Bernasconi says. "All the objects in mouse world are human objects. Houses are made of drawers, with drapes on top. We had little buttons and little ropes, and little needles and carpets. And then we had rat world and the human world. Honestly, when I saw rat world, I thought, 'I'll never finish this.' " e artists couldn't paint each surface, of course, so the team developed procedural methods to drag and drop patterns that au- tomatically surfaced marble, stone, wood, rocks, and so forth with random variations. "Evgeni said, 'Yeah, that's nice, but it's too clean,' " Bernasconi recalls. "So, Tom Maw- bi wrote a shader that automatically created dirt in the corners and streaks of water when it rained." e surfacing artists could place the dirt and streaks, and control the shader's attributes. To speed rendering, the team baked the dirt map into point clouds. Lighting the Way Once surfacing was under control, Ber- nasconi moved on to lighting. Light, in fact, is a central theme of the film: Light going away, light coming back, and, of course, a little ray of emotional light called Despereaux. Tomov's designs based on the Flemish painters called for rich lighting with large areas falling into soft shadows. Barry Armour, who had worked at In- dustrial Light & Magic as a CG supervisor, joined the Despereaux crew in that role and later became visual effects supervisor for the project. "We used light very carefully," he explains. "We paid homage to the type of lighting in Vermeer paintings. What we did isn't groundbreaking technically, but it was a real pain to achieve with furry char- acters. e approach I used was to light the sets and pop in the characters using that lighting setup, and add fill lights when needed—and, hopefully, the first render out of the box would be decent. e char- acters would move in and out of the light and integrate into the scene." It would have been impossible to calculate ambient occlusion for every hair on a frame- by-frame basis for the mice and rats, so Ar- mour devised a clever method to achieve the same result. "We'd do an ambient occlusion pass of the character's skin without the fur," he says. "And then, we'd multiply in the fur as a modulator of that overall ambient oc- clusion. at gave us enough detail to retain the soft look and still retain the shape." To light the sets, the artists shot an envi- ronment map from a central location and used it as the ambient map. "at pro- duced some bounce light," Armour says. "We also could do indirect diffuse lighting using bright objects, like windows, to light rooms and produce the soft light you see in the film. e challenge was to keep the light soft enough to look like a motivated light source for these characters." To avoid the cost of rendering physically accurate volumetric light for the environ- ments, Bernasconi wrote a shader that sim- ulated volumetric light by spraying Render- Man Ri curves. e technique also gave the artists specific control. "e Ri curve is a normal curve that RenderMan can draw as a ribbon," Bernasconi explains. "So, I wrote a simple shader that allowed artists to change the shape to simulate a volumetric light, tapering at the source and falling off at the end." Artists could control the shape using Maya curve ramps by, for example, moving a point to change the falloff, and then could see how the ray would behave At top, Despereaux (left) lands in rat world, where his rescuer, Roscuro (right), shows him the one shaft of light in the dark world that was designed to look more Hieronymus Bosch than Vermeer. At bottom, lighting artists first lit the sets, and then moved the characters in and out of the lights.

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