Issue link: https://digital.copcomm.com/i/30784
CGI n n n n forth to a basic material. “The materials prop- erties are a script, a giant text file written in the Studio scripting language,” Hill says. “In that file, we describe the color, specularity, rough- ness, density, transmittance, all those things.” In practice, a materials artist might start with a base color, add three-dimensional noise to modulate that color channel, adjust the fre- quency of noise, and modulate the hue, satu- ration, and value of the color. Then, the artist might add another procedure that changed that result, and a third that modulates the re- sult of those two, and so forth. “To create pores, we throw on a cell-noise procedure, flip it around, and play with tan- gents and constants to get it to look like pores,” Hill says. Another procedure mixes two mate- rials to create, for example, rosy cheeks. And, using volume procedures, they can add freck- les and moles in specific areas. “Imagine a spherical volume with every- thing inside as a one and everything outside as a zero,” Hill explains. “I can pop Linda onto the screen, locate her cheek in space, and put a sphere there that I scale, rotate, and translate to a specific location. Then I can sculpt some cell noise to make freckles, and put little cells inside the sphere. We combine procedures in Rio in Stereo The stereo team starts laying out their cameras at the same time as the lay- out artists create the initial camera moves. “As soon as layout completes a sequence, we create the left eye,” says Dan Abramovich, lead stereoscopic technical director. “We have special tools all across the pipeline—proprietary software for the camera and how it interacts with the renderer, tools for set- ting up the camera and controlling the variables, sequence-based tools, view- ing tools, rendering tools. We’re able to view stereo imagery all the way from [Autodesk’s] Maya to [The Foundry’s] Nuke.” The major change with this film was in how the artists used depth of field. They began experimenting with the technique in the third Ice Age film but removed it, and then approached the idea again with Rio. “We defocus the background,” Abramovich says. “And, we use a lot of rack focus. In some sequences, defocus became a visual effect. Instead of re-ad- justing the defocus, we’d let it stay and offset colors to create a magical shim- mering effect. We leapt off into a new creative area. We had the defocus and the depth. Now we had beautiful light blooms. We animated colors between the left and right eyes. The slight offset gives the image a pixie-dust feeling that you see only in stereo.” The magic happened accidentally. “We discovered a slight difference be- tween left and right, and we decided to keep it if the background was de- focused because it felt magical. If they were in focus, it could be a problem. The shimmering lends itself to highly reflective material, like water. We also used it to create a nightclub feel, creating a stylized defocus with the club lights. It feels magical, but there’s a hugely technical process behind it. It’s never a home run. We had to put a lot of work into it.” –Barbara Robertson Animators could control nearly every feather on the wing by moving controls on a “quill.” That geom- etry then drove the position of all the little “hairs” in a so-called fur file, which described the feather. all sorts of ways.” An interactive renderer makes it possible for the materials artists to see the results of their tinkering quickly. “You can work strict- ly with the script, or, if you want to look and interact with an image, you can load up the quick render,” Hill says. “It grabs 10 or 15 machines to be your slave, and distrib- utes the rendering across those machines so you can render an area over and over as you tweak the numbers.” Cloth Simulation To move the characters’ costumes, the simu- lation crew evaluated several cloth simulators before settling on Maya nCloth. “We’re a Maya studio for the most part,” says Stichweh, “so staying within the same 3D package was a positive thing.” Then, they adapted the program to Blue Sky’s style of animation. “Our style is cartoony with squash and stretch, but simulation, by default, follows physically based rules,” Stich- weh says. “We created a lot of pre-simulation and post-simulation tools to adjust the sim to the animation style. Our bar for whether the simulation was successful was whether some- thing reads as cloth but isn’t distracting.” In sum, the system the crew created used garments rigged to move with a character’s body so that the animators could turn a switch and see that silhouette. “The cloth had the rig weighting of the body so, for example, a shirt bent with an arm,” Stichweh explains. “It wasn’t really simulation; it looked like Satur- day-morning cartoon cloth.” Then, a system called “Anim to Cloth” ran a script that automatically prepped the clothing for simulation. “We realized the task lists were the same all the time, so we automated the prep,” Stichweh says. “The system could even grab the default library for a particular garment, say Linda in a raincoat, and submit the simulation with- out anyone touching the file.” The rig had a switch that would send cloth- ing that didn’t need simulation—costumes worn by background characters in a crowd, for example—straight on to rendering. “If there was a simulation cache, it went to simulation,” Stichweh says. “No one had to keep track. If we cared about five characters out of 50 in a shot, we’d tag those up front.” Stichweh likes to think of the system they April 2011 15