Computer Graphics World

July 2009 52 n n n n CG I Steamy, Snowy Atmosphere Although proud of the performances that the animators created for the film, Das- trup and Gabor are quick to praise the rest of the crew. "e other departments did such an amazing job with the look of the film," Dastrup says. "We so often have sequences with a stylized look that's better than real life. It really draws you into the environment." Helping to create that environment was an effects crew comprising 12 TDs and two effects animators. "We were used to creating effects for the ice world," says Kirk Garfield, visual effects supervisor, "but the lost world contained effects we hadn't done before. In a nutshell, the biggest hurdle was the sheer volume of effects." Garfield e-mailed a list of 64 effects that the crew created—from bubbles to various types of water, with snow, stink bombs, steam, dust, mist, lava rivers, lava falls, lava pools, and many other effects in between. For the volumetrics, which include steam, smoke, and clouds, the studio had used an in-house technique called "smaug" in the past, in which they'd texture inter- secting spheres in 3D—in other words, at- tach attributes such as density and color to geometric primitives. "at limited the motion and look we could create," Garfield says, "so for this film, we evolved Smaug into SmaugVox. at allowed us to generate voxel data with Maya fluids that we exported to our [proprietary] Studio format, and render in voxel space within our renderer. In terms of motion, Smaug rendered Maya particles as foggy blobs that moved in whatever way a technical director might move the particles, which worked well for small effects. However, for larger areas and for interaction with characters, it was lim- ited. "e sheer number of foggy Smaug blobs you would need would cause render times to spike," says Andrew Schneider, ef- fects TD. On the other hand, "SmaugVox takes a Maya fluid volume and renders it as fog," he says. Because it is one volume, it renders faster without gaps. "In addition, you get a lot of cool billowing fluid motion for free, and the effects TDs don't have to force Maya particles to move naturally." As for the look, Hugo Ayala in the R&D department states that previously, when the objects described were semi-transparent, the raytracker had to push through the geom- etry and compute the contribution of all the elements inside in little increments as they moved through the volume. In SmaugVox, the process is simpler: Each time the tracker needs to compute a value, it interpolates it from the grid, the volume, rather than loop through all the Smaug geometry. is was especially important for a "Mist Monster" sequence during one of Buck's flashbacks, but the crew also used it for snow, dust, and other effects when it needed interaction between characters and these effects. Footprints in the Snow In the ice-age world, one interaction be- tween the characters and the frozen world happened constantly: footprints in the snow. In the past, some were texture- based, and some were 2D fluid simula- tions. None were interactive. "We needed something more robust for this picture because we had 100 shots to do," Garfield says. "We worked with R&D to come up with a tool that allowed more detailed control and interactivity." e tool, a plug-in for Maya, looks at the intersection of the geometry and the ground plane, and creates a displacement on the fly that a user could see within a couple of hours in Maya before rendering. Attaching snow to fur was another prob- lem solved in an efficient way for this film. Working with the R&D department, the team created a method, using Blue Sky's fur- generator technology, for retrieving the posi- tion of every hair on an animated character. With that information in hand, they could add or remove snow from the characters as they walked or fell through the snow, based on animated signals in Maya or at render time; or, they could accumulate it on the fur during a snowstorm and remove it when the characters brushed themselves off. According to Sean Palmer in the R&D department, they fed the point data into the studio's voxel-based particle renderer. "Rendering fur and particles in voxel space allows us to have millions or even billions of source points or curves that can be aver- aged into and rendered as a single grid," he New technology allowing more detailed control and interactivity than before helped technical directors at Blue Sky Studios put footprints in the snow for Manny and Ellie (above, left) and Sid's new family (above, right).

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