Computer Graphics World

October 2008 19 CG I n n n n plains with clouds, the effects team began by creating 3D volumetric clouds and then later moved to matte paintings. "ere was so much complexity on the ground, we lowered the contrast and detail in the sky," Peterson says. e 3D clouds provided a starting point for the painters. "We could get amazing visual results and behaviors with the 3D clouds," Gluck- man says. "And, the clouds are objects, so set dressers could place them in the set like they do with trees. But it was an extraordi- nary effort to light the clouds all the way. So, we'd put light through the volumes, but not take it to 100 percent." e effects artists created the clouds us- ing volumes inside volumes. Peterson ex- plains by drawing one cloud circle. en, he draws little circles of clouds on the edges of that large circle, and draws more circles inside. "We rendered the clouds as spheres of density," he notes. "We had millions in a single cloud to provide detail." A new light- ing tool gathered light from the environ- ment and transmitted it into the clouds. Keeping It Simple In addition to the grass and clouds, the ef- fects department handled crowds, trees, flu- ids, cracked earth, smoke, mist, and dust. e studio's crowd system distributes and plays pre-baked animation cycles, but in the past, animators could change little more than eye direction in the simulated crowds. With this film, the animators gained the ability to use the data assigned to each character by the system, which gave them, in effect, a quick start for working with individual characters in small groups. "Toward the end of the movie, we have 20 tourists close to the camera," Gluckman says. "We used the crowd system to rough- in the animation, and then we handed it to animators to refine." For the trees, Peterson and the effects team completely changed the procedural system they had developed and used on previous films. Instead, using tools inside Maya, the artists interactively modeled the trees. "e modelers created the trunks for the procedural system anyway," Peterson says. "And, when we were trying to decide on the look for the new trees, we realized that they would model a branch, duplicate it, resize it, and stick it on itself." So, rather than using parameters and rules as before, they built a tool they call Bonsai that makes the model- ers' techniques for growing trees even easier. "We just click on a branch and add more," Peterson says. All told, the crew created close to 60 species of trees and five or six varieties within a species. "ere was a lot of copying and pasting going on," he says. Peterson also devised a simpler method for working with fluids, to splash lava from a volcano, pour water from a dam, and so forth. Working within Maya, the effects team used smooth-particle hydrodynamics to put fluid forces onto particles. And, they also used a new tool that Peterson created. "A lot of people do fluid research to sim- ulate fluid dynamics using physics," Peter- son explains. "But, I know how I want a splash to look. So, I thought, 'Let's build a force that puts particles into a fluid-like shape without regard to physics.' Because I'm not concerned about proper [physical] forces, it works very fast." To do that, Peterson wrote a field in Maya that creates chains, that is, strings of particles. "It looks at the particles and tries to find local patterns," he says, "and then nudges the particles into chains to enforce that grouping. It looks very natural." For the parched earth, however, the crew brought texture maps into Side Effects' Houdini to crack the ground geometry. ey created volcano steam with wispy curves rendered as tubes of density. And, a new tool written by effects artists Greg Hart and Nick Pavlov automatically rotat- ed particles in a dust cloud created by the plane crash to create a vortex. "We use our own tools for rendering, but for particle simulation, we use third- party tools," Peterson says. "We do a lot with particles in the render stage, though. We have filtering tools for clustering. We drive normals off particles and project par- ticles. And, we light all the geometry in proprietary software." e Madagascar 2 crew at PDI/Dream- Works, many of whom also worked on the first film, could have relied on tools and techniques that helped Madagascar score nine Annie nominations. Instead, they pushed the state of the art with new char- acters, a more demanding location, and a multilayered, emotional story. By incorpo- rating live-action camera techniques and the expertise of an Oscar-winning cinematogra- pher, they enlivened the visual quality of the film while simultaneously giving the layout artists a method for quick experiments. And the technical crew, while appreciating the need for realistic landscapes, found ways to accomplish the realism without using com- pute-intensive physical simulation. e movie may be wacky, but the home- spun production was definitely smart. n Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at BarbaraRR@comcast.net. Effects artists at PDI/DreamWorks typi- cally use commercial software for particle dynamics (at top), proprietary rendering software to add such effects as clustering to the particles (middle), and proprietary lighting tools to produce reflections for the final image (at bottom).

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