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n n n n Simulation To handle the fire and other volumetrics, Animal Logic’s R&D team created an in- house fluid-dynamics system they call Snap, for the 40 effects technical directors on the film to use. “Tey wrote it from scratch us- ing SIGGRAPH papers,” Green says, “and added it to ALF (Animal Logic Fundamen- tals), a node-based procedural system.” To achieve the high-resolution detail for fire and smoke, Snap distributes the simulations on 32 to 64 processors. “Te fire on this film is amazing,” Guns- berger points out. “I haven’t seen any other film with the kinds of fire effects we have. Especially in stereo.” Green describes one scene in which an owl surfs a wall of fire curved like a wave. “Te Snap developers would start with a regular expensive fire simulation and then push velocities around in a curve,” Green says. “We used a lot of wavelet turbulence so we could run the simulations at low res to check the bending and that it was moving at the right speed, then we added detail to get a defined shape.” For rendering, the crew used Pixar’s At top, modelers, riggers, and surfacing artists created perched and flying versions of each owl to use as benchmarks. At bottom, the owls fly through painted and volumetric skies, and over landscapes in various levels of detail. bushes and smaller plants. Ten, they saved that information in Animal Logic’s in-house shading system, using proprietary shaders to apply materials and textures. “Every limb of the Great Ga’Hoole Tree is like a forest,” Jowell says. “It has multiple lay- ers of plants—vines, ivy, moss—all this crazy stuff.” Because the foliage is procedural, the artists added wind at render time that rippled through the vegetation. Most of the environments in Legend are organic, even those with architecture of a sort constructed by the owls. “Te idea was that if this was constructed by anything, it was con- structed by ancient owls,” Jowell says. “So there are slight owl shapes in the designs. Tere are a lot of carvings and the sense of an historic coliseum, but it is all rubble.” Jowell’s team discovered that creating an organic environment was more difficult than they had expected. “Rocks, in particular, have erratic flows,” he says. “Tey don’t have lines that complement each other, but they do have a specific look, and it’s obvious when they don’t look right. Surfacing-wise, it’s all chal- lenging.” As much as possible, the crew relied on procedural surfacing, with hand painting to add details. 16 October 2010 To make it easy for the animators to load the complex environments, the crew provided maps. “We broke the environments into sec- tions,” Jowell says, “and for every environment in a scene, we passed along a section map to give the animators an idea of what was in the background that they didn’t need to be con- cerned with.” To animators working on scenes, the forest trees and vegetation could appear as bounding boxes to lighten the scene. For the far backgrounds, the team used matte paintings. “In some places, we projected matte paint- ings on top of geometry,” says Jowell. “Te art- ists painted a lot of sky backgrounds. But, the owls fly through volumetrics. Every time we see the sky, we’re seeing a combination of volumet- rics and matte paintings.” Setting the Atmosphere Nearly every sequence in the film has some kind of atmospheric effect—clouds, fog, fire, and other volumetrics. “People thought we were mad,” says Miles Green, one of three ef- fects leads on the film. “We were starting a film and didn’t have a fluid system for fire or smoke. But, two years later, we had a fully working pipeline. It was a major achievement.” RenderMan, the studio’s proprietary Maya- to-RenderMan software, called MayaMan, and a proprietary shading environment. “We’ve always had a node-based approach to shaders,” Gunsberger says. “Rather than hav- ing shader TDs write one shader with many controls, our shading system builds networks from components. If we have particular shad- ers with complex networks, like the feather shaders, we will give that to a shader TD to optimize and bake out as a single shader.” ALF created the feathers on the fly at speci- fied levels of detail, drawing every barb and feather with curves when close, and slowly changing the detail to flat geometry as the bird moves away. “We also used image compositing exten- sively,” Gunsberger says. “If there were slight animation tweaks, we didn’t want to re-render volumes. We rendered deep passes, sampling data along the entire depth of the pixel.” Whether Legend achieves the same success as did Happy Feet remains to be seen, but for the crew at Animal Logic, the work achieved is a feather in their caps. “Every time we were asked to do something, like the fire or the feathers, we’d think, ‘Tis is impossible,’ ” Green says. “But we carried on and went for- ward another step.” n Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at

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