Computer Graphics World

September 2009 19 CG I•Stereo n n n n from camera and the hairs became too small, the system automatically thickened them and used transparency to render the fatter hair. "We accumulated a lot of transparency," Kramer says. "But we didn't have aliasing artifacts, which would have been expen- sive. e big challenge with inexperienced lighters was optimizing scenes to make the raytracing efficient." Arnold provided other advantages, though. Because the raytracer rendered en- tire scenes, and because the modelers built entire city blocks, the artists could freely move the camera and see fully rendered scenes. Kramer provides an example: "We were test-shattering a building by dropping a banana into it. e rendering artist placed cameras all around the building so we could intercut close up and far away to create the shot. To our surprise, when we looked at the backside of the building, we saw glass busting out. We didn't know that was hap- pening. Being able to set up lights for one simulation and get coverage without having to explicitly dial each view was cool." Food Fight Although modelers, animators, and light- ers adhered closely to the production art- work in order to create the stylized, satu- rated look of the film, effects artists were left largely spinning on their own. "e only area where production designers gave us guidance, but didn't take us all the way through, was in the area of effects," Bredow says. "ey'd give us inspirational paintings, and our effects supervisor Dan Kramer and his team worked out how things moved. It was great to give them a playground for blowing our socks off." At first, normal-size food rains down, but in the third act, the townspeople must fend off massive amounts of colossal chow. "We drop food that's made of more than one piece, and that interacts with whatever it hits," Bredow says. "A pancake hits a school. A jalapeño pepper explodes into a giant fire- ball. e interactions are extreme." To handle the dynamics—the dropping food and the destruction it caused—the crew used the open dynamics engine (ODE), a rigid-body dynamics solver that the studio had integrated into Houdini for previous films. By connecting many rigid bodies with joints, they could simulate soft bodies, like food, as well as hard bodies, like buildings, and more easily simulate the interaction between them. In sum, operators in Houdini shattered objects into complex, low-resolution parts connected with breakable constraints, simulated through ODE, and parented team used multiple cameras to help enhance story points. "Sometimes you might increase the interocular to make a character round, but that makes the whole scene too deep and separates the characters too much in depth. So, we might use multiple pairs of cameras to adjust convergence and interocular for characters and objects independently in the background, midground, and foreground." In one shot, for example, the mayor, who had been a small man, has eaten so much free food that he's grown im- mensely. "Flint barely recognizes him," Anderson says. "So we really tried to play with his roundness." One difficulty the stereo team had with Cloudy was that the scenes were so complex they couldn't always dial in the cameras interactively. "The entire town was a model," Anderson says. "It took so long to open the files, I'd give a camera artist parameters, say, an 8.6-pixel offset. The artist would make the change, and then we'd bring up the scene and review it." The huge town also made bal- ancing the depth in the establish- ing shots tricky. "The city scenes used such wide lenses, we didn't have a lot of depth at that distance," Anderson says. "But, if we gave too much depth to objects far away, they looked like miniatures." One thing the crew learned with this film, though, is that they can push the depth back farther than they once thought. "We've learned that our eyes are more flexible than we've given them credit for," Anderson says. "This stuff is all so new that for the first set of films, we concentrated on get- ting stereo 3D right technically. Now, we can start breaking the conventions to use it creatively." No better event than a food fight. —Barbara Robertson The subject matter of this film, falling food creating catastrophic weather, created the perfect opportunity for stereo gags.

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