Issue link: https://digital.copcomm.com/i/77744
CG Animation n n n n by hand," Sheffler says. "Now we fill a new character full of a kind of jelly, put an armature inside, pose the armature via simulation, and use that to extract shapes for rigging. We can have a fully, nicely simulated, rigged character in a couple days." The new system also automates the process of balancing blendshapes in faces and makes the process of rigging multiple characters easier. "You could think about a character as the sum of artistic opinions," Sheffler says, explaining that a character's rig file contains those artistic opinions, the decisions made as the rig evolves. "It's like a painting or drawing, except with a lot of ones and zeros," Sheffler says. "If you were to look at it over time, like a time-lapse, you would see the artistic opinions in a par- ticular syntax iterate and change slowly. You want to have a nice way to put those opinions in a global repository." Presto provides that global repository, Presto integrates simulation—volumetric flesh and ballistic skin—more closely. This was par- ticularly important in Brave for Merida's pow- erful horse Angus and the svelte mother bear. In addition, the new system provides inputs to external, proprietary cloth and hair simula- tion systems, each of which incorporated new methods and technology developed for Brave, and the various other simulation systems used at the studio, as well. All the departments, including simulation, shading, lighting, and effects, needed to redo workflows to connect with the new animation system. No question, a major undertaking. work from one to multiple places in a dynamic fashion. Now, we can mix and match layers and define how one inherits another—the shape of a face, maybe, or a control within a face. We have a space in which the system can interpolate those artistic opinions." To flex characters' muscles and jiggle skin, Bear-ly There To move muscle and skin for those characters, Pixar used the PhysBam system (developed at Stanford) for the second time. "We had started working with muscle rigs for Bob in The Incredibles," Wise says. "But the first time we used the PhysBam volume simulator was to create big and jiggly humans in Wall-E, the Captain in particular. We wanted him to have believable mass, weight, and jiggliness. We also used it in the big final sequence with the humans sliding down and piling on top of each other. But, we hadn't used it since, until Brave. So, using PhysBam was not new, but we spent a lot of time experimenting with simu- lated muscle rigs." To make Angus's muscles look as if they ex- pand and contract as he gallops through the forest, the team ran volume simulations atop an articulated, underlying musculature. "We' build a 3D volume out of the high-resolution skin mesh, fill it with tetrahedrals, and con- form it to the shape of the final skin mesh," Wise says. "We ran the volume sim on that 3D tetrahedral mesh and warped the skin mesh to the results of the simulation." As a result, the skin looks as if it stretched over the muscles appropriately. To jiggle the skin, the team used a second simulation. "We take the surface mesh, after it has been warped with the volume simulation, and then run a skin simulation," Wise says. "That simulation slides in the plane. It doesn't break the silhouette; it slides along the surface. We attach hair to the result of that simulation, and then run the hair simulator." The bear was a different challenge. "The bear has looser skin and flesh," Wise says. "Having the bear feel alive, getting the feeling of mass and weight, meant feeling that flesh move. So, we used more traditional articulation with vol- ume and skin simulations, less-defined muscu- lature, and thicker fur." d Hair Brains At top, tailors modeled the clothes using 3D tools for the Brave characters, rather than creating costumes from 2D patterns, as on previous films. At bottom, traditional articulation with volume and skin simulations, less-defined musculature, and thick fur helped give the bears mass and volume. which gives character riggers flexibility and speed: They can move rigs in part or wholly from one character to another. "Say you want to see the work on master characters propagat- ed into hundreds," Sheffler says. "This is a class system we couldn't do in the past—pushing plex we've made," Sheffler says. "We're consis- tently upping the bar internally. And if that weren't hard enough, rebuilding the tools to do the film was an additional challenge. It was a large tax on the technical side in many ways." "The characters in Brave are the most com- The studio estimates that 96 percent of the shots in Brave had some form of simulation. To handle hair and cloth simulation, Claudia Chung led a team of 16 simulation artists, five tailors and four groomers, and four simula- tion leads. In addition to work specifically on shots, the team handled changes to the pipe- line caused by the switch to Presto. "We have people with varied backgrounds," Chung says. "Artists and tailors, and one has a masters' degree in physics. Some have back- grounds in computer science and program- ming. We built our team to have a full gamut of backgrounds and to rely on one another. June/July 2012 15