Computer Graphics World

touille's characters, Presto is stationary for a long time, and then he accelerates fast and moves quickly. When that happened, the skin went through the cloth before the cloth knew what was happening, and the skin stayed on the wrong side. "We had to go back and do simulations at high speeds or fi x simulations after they'd been done," Apodaca says. "It was really a question of speed. You can run a simulation at four or eight times the frame rate so the skin doesn't move far enough to penetrate the cloth, but even then you get funny folds or little pokes, or things get snagged." Also, cloth fi x tools used in Ratatouille helped the team pin, glue, and grab pieces of the mesh in Menv to pull them into order. e curtain was equally diffi cult, but for diff erent reasons. "It's deceptive," Apodaca says. "In terms of tailoring, it's as simple as you can get. It's a big, square piece of cloth. But, it's extremely heavy and very long, and the numerical calculations don't appreciate all that weight." As a result, it was diffi cult to get it to hang like a real curtain and fold properly when opened, a problem solved only with much iteration. Moreover, the curtain had tassels. "We wanted it to look like gravity placed the tassels, not like someone placed them in computer graphics," Apodaca says. "So we held the tassels above the ground, with the big ball at the top of each and all the little fringes hanging down from that, and then used cloth sim to slowly push them to the ground. e inter-fringe collisions gave each one a nice random shape. Even though they just sit there for most of the fi lm, if we had put them in place with Maya, they would have looked mechanical." For the theater crowds, created with a li- brary of mix-and-match heads, hair types, jewelry, and body shapes, the crew used the crowd animation system from Cars. Animators created such actions as clap- ping, head turning, and so forth, as well as a standing ovation. "We tossed them onto the characters at random," Apodaca says. "It was a relatively old-school simulation." Because the initial storyboards had several shots of Presto looking into the crowds, to make it possible to render the 2500 theatergoers, the crew put higher- resolution characters in the fi rst few rows, lower-resolution characters behind them, and then had consistent shading across the entire audience. "As the story evolved, we had fewer shots of the crowd because it detracted from the pacing," Apodaca says. "If we had known, we would have put less eff ort into them and they would have looked worse. So, it was a happy accident." A ' Toon Type of Motion Blur e biggest technical innovation for the fi lm was in how the crew handled mo- tion blur. In 2D animation, a cone-shaped streak with speed lines indicates fast mo- tion. Apodaca didn't want to replicate that look, which would have given the fi lm a 2.5D appearance, but he wanted to get the sense of cartoon motion blur. Dana Batali, head of the PR Ren- derMan group, helped provide one answer: "We changed the shape of the motion blur in the shutter of RenderMan to a more triangular shape," Apodaca explains. "It spends more time sampling at the end of the frame, the fi nal position, than the front, so the front edge is dense and opaque, and the back edge wispy, undersampled, and transparent." en, the second answer: ey blended a non-motion blurred frame that had sharp edges with the new triangular motion blur streak. e result produced an image in which you could see the characters' silhouettes, but with enough blur so when they moved, it gave the impression of speed. "We did this only on the charac- ters, not the background," Apodaca says. " at's also an homage to the way cel is done, with beautiful watercolor paint- ings in the background." Being able to create a 'toon was a joyful experience for many on the crew. "Many of us are in animation to begin with because of cartoons, but we're never able to do them," Sweetland says. " ere was noth- ing better I could ever witness as a direc- tor than to see people hurl themselves at the work with unbridled abandon. I think 'Presto' is a really good combination of an old cartoon and a Pixar movie." At the end of the fi lm, Alec gets his reward. e rabbit has replaced the hat on Presto's poster, and a bouquet of carrots sits next to the bouquet of fl owers. As for the Pixar crew? eir rewards have only just begun. ■ Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at BarbaraRR@comcast.net. The storyboard and production design sketches show the elaborate stage on which Presto performs, the size of the theater, and the number of people in the audience. Top, the spotlight shows how far Presto will fall. Bottom, the heavy curtain became an interesting challenge for the cloth-simulation team, as did the crowd creation and simulation. ■ ■ ■ ■ CG Short Films February 2009 24

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