Computer Graphics World

and supplied lighting reference for the postproduction crew. At Tippett, real animals—a wood rat in a local wildlife rescue facility and three iguanas that visited the studio—provided modeling and animation reference. "None of us had seen a wood rat," says James Brown, who supervised the 16 animators on the fi lm. "We watched him burrow and climb around in his cage, and then used his mannerisms, his fast metabolism, and high tempo." e opposite was true for the iguana. " ey use as little energy as possible," Brown says. "Most animals settle them- selves into a comfortable position when they stop, but if an iguana is crooked, if its elbows are bent funny, it doesn't matter. ey don't move. We used that to our advantage; we really played up the contrast between the two." e technical challenges concerning the two characters centered on Chico's scales and Manuel's fur. Tippett uses a pipeline based on Autodesk's Maya, Apple's Shake, and Pixar's RenderMan. In ad- dition, modelers use Pixologic's ZBrush and Autodesk's Mudbox. Scott Liedtka, CG supervisor, managed the technology, working with R&D to create solutions for problems beyond those the commercial packages provided out of the box. For Chico's scales, the technical crew started by working with a procedural shader to cover his skin quickly, and then realized it wouldn't work. "He's an organic animal and every scale was dif- ferent from every other depending on where it was and how the anatomy fl owed," Liedtka says. "So, because we had spent time on the shader, we thought maybe the painters could use it as a starting point. But, we ended up throwing that shader out." Instead, the painters put scales onto the creature using dis- placement. en, to create the undercutting that is so diffi cult to achieve with traditional displacement, the technical crew de- vised a technique they call "vector displacement." "One of the ways we [create the undercutting] is to use ZBrush or Mudbox to create two models," Liedtka explains. " en, we diff erence the two models. We developed a shader that can take the diff erence and create a displacement along a vector rather than along a normal. It's a way to capture model detail in a displacement map. e modeler models. We process the models and turn them into vector displacement maps." A second Chico challenge was his dewlap. "Every time the iguana moves, this fl appy piece of skin has to move realistically underneath him," Liedtka says. Because the crew didn't want to spend computing resources by simulating the entire iguana model, the technical directors removed the dewlap, simulated it separately using Maya NCloth, and then stitched it back onto the model. For the creature's muscles, the TDs used the CMus- cle plug-in for Maya, now off ered by Autodesk. Rat Problems Manuel presented more problems. "Our main concern was that he was too ratty," Brown says. "We were afraid people would be disgusted by him and wouldn't empathize with him." Because an- imators work with a malleable rig, they adjusted the rat's behavior to make him more appealing, rather than asking the modelers to make changes. "We dipped his head down to make his eyes more prevalent and brought his ears forward so you'd see him as a big- ger, rounder shape, to make him a little cuter overall," Brown says. "We also didn't let his arms get too far from his body, because as soon as you do that, he becomes too human." e eff ort to make the rat more adorable also put pressure on the pipeline. " e art department kept pushing us to have more and more hair," Liedtka says. " ey wanted him to look softer and softer, cuter and cuter. We were running out of memory, but once the director signed off on the character, we had to fi gure out how to get the rat to render." First, Liedtka and his crew looked for other memory hogs— for all the problems they needed to solve. One issue was the number of layers. "We do breakouts for compositors when we create characters, and we were up to 27 breakouts between the fi ll lights, specu- lar, shadows, color codes for diff erent features, and so forth," Liedtka says. "If we turned all of them on, sometimes the sys- tem would crash." In addition, they looked for ways to reduce render times for Manuel close-ups, motion-blurred action shots, and other shot-specifi c problems. Lastly, they discovered that a Tippett created emotional performances for the two digital characters Chico (left) and Manuel (right) with support from a technical team that grappled with the creatures' CG scales and fur. Images ©2008 Walt Disney Pictures. Courtesy Tippett Studio. and supplied lighting reference for the postproduction crew. At Tippett, real animals—a wood rat in a local wildlife rescue facility and three iguanas that visited the studio—provided modeling and animation reference. "None of us had seen a wood rat," says James Brown, who supervised the 16 animators on the fi lm. "We watched him burrow and climb around in his cage, and then used his mannerisms, his fast metabolism, and high tempo." e opposite was true for the iguana. " ey use as little energy as possible," Brown says. "Most animals settle them- selves into a comfortable position when they stop, but if an iguana is crooked, if its elbows are bent funny, it doesn't matter. ey don't move. We used that to our advantage; we really played up the contrast between the two." e technical challenges concerning the two characters centered on Chico's scales and Manuel's fur. Tippett uses a pipeline based on Autodesk's Maya, Apple's Shake, and Pixar's RenderMan. In ad- Images ©2008 Walt Disney Pictures. Courtesy Tippett Studio. October 2008 35 Animal Modeling ■ ■ ■ ■

• Cover