Issue link: https://digital.copcomm.com/i/77744
CG Animation n n n n as well. Again using the phone cord example, if you were to fling a phone cord very fast, it would uncurl and then bounce back into place. With the system Witkin devised, the same thing happens with Merida's curls: They length- en, but at a certain point, snap back into place. "This was Andy's model," Chung says. "He was all about phone cords. His way of explain- ing things was the key to understanding what the problems were." Sadly, the new system, named Taz, was The tailors created the kilts by stitching together 2D panels into an accordion shape, and then had the cloth simulator relax the accordion into soft folds. curve," he explains. "Then, we bend them. It's very interactive. We define the curl and sculpt how we want the curve to flow." Shapes de- signed around each key hair define a shell that fills with interpolated hair at render time. "We spent months and months sculpt- moving into full production when Witkin died, September 12, 2010, in a scuba diving accident. "I remember about that time doing weekly walk-throughs with Andy," Chung says. "He would visit every technical artist and help us figure out whether a problem was a production problem or a core problem. He was very much like a teacher. The very fact that I can explain this to you now is because he was able to explain it to me." Hair She Is To create Merida's curly hair, Elinor's long braids, Angus's main and tail, or all the oth- er characters' hair that Taz would move as the characters delivered their performances, groomers started with a bald model and then placed and defined key hairs. "Merida's hair was hardest," Chung says. "Angus's was the most complex." Indeed, Merida's hair stylists spent months placing curves on her scalp that represented the curls—1,500 curves that became 111,000 curves in the final render. To create Angus the Clydesdale's hair, groomers hand-placed 111,000 curves that became 1.8 million in the final render. Wise describes the process: "We lay down a curve in 3D space in Maya, and click, click, click, put control points on the ing and tweaking to get the parameters just right," Wise says. "Merida's hair was directed to within an inch of its life. This forelock must go here. It must be this thick. It must curl that way." The groomers Merida's scalp starting with the innermost layers, working up her head to the outermost, positioning the key hairs with the simulator in mind. "Mer ida's curly hair was so massive and attached the hairs to interwoven together, the challenge for Lena [Petrovitch] was in keeping it from becom- ing a rat's nest," Chung says. "To have control over the artistic design, she decided to groom Merida's hair in an antigravity way, almost as if Merida had touched a light socket." Once the groomers finished styling Merida's curly mop, they sent all the data to the simula- tor and turned on gravity. When the hair re- laxed, the artists evaluated the look. Did it sag too much, as if she had just gotten out of the shower? Is it too stiff? "We had a whole suite of calisthenic tests slow-motion shots to be sure the simulator could handle those situations and that the parameter settings were correct. People say, '[With simulation] you get the motion for free.' That's the funniest thing. Yeah, it's for free—after three years of development and months of iterations." Once the crew untangled the challenges in that we ran the characters through to see how the hair behaved," Wise says. "We turned their heads left and right, animated them jumping up and down, twisted their torsos with their arms out to the side. It's an iterative cycle that goes on until we have it just right. Later in production, we ran fast-motion and creating Merida's curly hair, they moved on to Angus's straight hair. "Those were our test pieces," Chung says. "Once we figured those out, our other characters fell into place." The groomers grew Angus's hair in exactly the way a horse's hair would grow, following the contour of his muscles. The challenge was in creating appropriate motion for his long, silky mane and tail. "We wanted it to move and hang luxuriously," Wise says. "It was less of a grooming challenge and more of a param- eter-tweaking challenge. He has some of the most extreme motion in the film." Angus might be swishing his tail in one frame, galloping through the forest in another at speeds no horse could achieve, and coming to a stop more quickly than would be possible in reality. However, the simulation engine uses the laws of physics, those for velocity and grav- ity, to move the digital hair, which sometimes resulted in hair moving in non-artistic ways. So, the artists essentially tricked the simulator, using various knobs, levers, and parameters to dampen the motion when necessary and move the hair with "cartoon physics" instead. That was true for the other characters, as well. For example, Merida might turn her head quickly, causing her hair to cover an eye during an important emotional moment. June/July 2012 17