Issue link: https://digital.copcomm.com/i/18322
CG Characters n n n n To create Kitty Galore, the Tippett crew watched countless videos of Sphynx cats, a rare breed known for its lack of a coat. Compositor Shel- ley Campbell, who owns such a pet, brought it into the studio so the team could see up close how much muscle shape and movement was visible at the skin’s surface, and how the skin wrinkled. “Having refer- ence like this was priceless,” says Eric Jeffery, lead character rigger. Te CG Kitty Galore was built in Autodesk’s Maya. For the muscu- lature, the puppet department created a detailed muscle system using Maya Muscle for simulating muscle bunching and jiggling. Te artists also used the muscle system to simulate bones—such as the scapula— moving under the skin. According to Jeffery, due to the countless variables at play in a cat’s anatomy, a Sphynx cat’s wrinkles rarely appear the same way. “Because we were able to spend time watching our reference cat, we were able to isolate the most commonly occurring wrinkle patterns and re-create them onto our digital Kitty puppet,” he says. To achieve the realistic wrinkling, the group had to develop a tech- nique that used tangent space vector displacement driven by a com- bination of strain from the mesh and a pose space system for prob- lem areas that needed specific sculpts. In addition, Kitty required fur system development, skin-shading improvements, and a beefy muscle system—in addition to the studio’s facial animation system and anima- tion rig to support her over-the-top acting. “All the departments were pushed pretty hard to get her to work,” Liedtka says. Specifically what made Kitty Galore so difficult to create, according to Mike Farnsworth, graphics software engineer at Tippett, was the fact that she had so many wrinkles and that her muscular definition changed as she moved, making it too difficult to track those variations manually. Alternatively for her skin wrinkles, the modelers created a form of vec- tor displacement for use in Pixar’s RenderMan that followed her anima- tion and enabled them to mix as many as 75 displacement maps based on her movement and dialog. Te data for mixing the wrinkle and muscle sculpts was generated with custom Maya plug-ins that analyzed her skin stretching and facial poses. Te sculpts themselves, which were the basis of the maps, were created in Pixologic’s ZBrush and Autodesk’s Mudbox as high-resolution meshes distilled down to fairly large EXR images with a custom tool that operated on the GPU. “Our incarnation of vector displacement is encoded in tangent space, with some special handling for texture seams. It works fairly well on subdivision surfaces, our primary mesh type,” says Farnsworth. “Te pose plug-in within Maya handled natural transitioning between sculpt mixes. We don’t know of anybody using that same flavor of solver that we used on Kitty.” Te final displacement shader was somewhat complicated, says Farn- sworth, as it took into account all the mixing data and all the displace- ment maps. “It had to be optimized to minimize the number of dis- placement maps used, or the texture-caching system would have slowed to a crawl,” he adds. It was important that the shader synchronize with Tippett’s fur sys- tem so that the fur on Kitty’s body tracked with the wrinkles. Tus, The CG Kitty Galore interacts with the CG mouse, Scrumptious. Images courtesy Warner Bros. Pictures. October 2010 35