Issue link: https://digital.copcomm.com/i/6960
February 2010 28 n n n n Simulations e character developers skinned the low- resolution model, which allowed for quicker iterations, and animators created the per- formance using that model in Maya. en, the team moved the high-resolution ZBrush model to Maya and used a wrap deformer to have the low-resolution model drive it. In oth- er words, the high-resolution model moved using the low-resolution model's performance. In addition, the artists layered a static displace- ment map on top. at system worked for all three characters, but Hades, which is made of lumpy, cracked charcoal, with lava oozing in the cracks, had an additional complication: He appears out of a bonfire. And fire envelops his wings. "We see the fire close up," Rocheron says. "So, we spent a lot of time trying to get the simulations to be in as high resolution as pos- sible. Generally, fire is on a large scale, and what matters is the overall motion of the fire, not the details in the fire. But, this fire is big in terms of scale, and it's in front of the camera, so you can read the details within the fire." us, rather than simulating the fire at a res- olution sufficient for overall motion and then using 3D textures to add details, the effects art- ists decided to run the simulations at extremely high resolution. "Usually, we simulate fluids at a voxel size of five to ten centimeters," Roche- ron says. "is time, we brought the size down to a millimeter, or less on some shots." e crew used Scanline's Flowline software for the simulation. "e good thing is that with the last version of Flowline, we aren't limited to a bouncing box for the simulation," Rocheron says. "e software builds the vol- ume as the fire expands." Crowding the Face A second challenge for Hades was that the character sometimes looks like actor Steve Coogan, and sometimes like the big, burnt, lord of the dead, and this CG version needed to perform with Coogan's expressions. To cre- ate the performance, the crew used Mova's Contour Reality Capture system. "We captured Steve [Coogan] saying all the lines of dialog and doing a range of facial ex- pressions using the FACS system," Rocheron explains. "en we retargeted the 593 control points to our Hades model, and they drove the deformation of the skin. We wanted to avoid going through a blendshape system. We tried to keep as much of the original performance as we could." In addition, to tweak Hades' performance in areas and for angles they couldn't see in the captured performance, the crew used Alice, the studio's crowd software system. "When you an- imate crowds, you work with motion-capture clips and the software figures out how to blend them together," Rocheron says. "So we used the crowd software to blend motion-capture clips and to work with layers of animation. We could use a clip from a performance on one part of the shot and another clip from the second part of the shot, and blend them together." For the fiery skin, the artists converted the fire simulations into point clouds in Pixar's RenderMan, and used RenderMan's color- bleeding functions to apply color from the fire onto the character. "Usually, you have lights around a character, but for this character, the main light source is his fire," Rocheron says. Rocheron counts art-directing the fire as the biggest challenge for the show. "e fire was such an important component of the character," he says. "But art-directing fluid simulations in a precise manner is very difficult and tricky. When Hades leans forward, we needed the fire to grow in that direction. When he's angry, the fire need- ed to move faster. It took time to identify which components of fire made the difference, but once we found the rules, it became quicker." "is project has so many choice bits," Mack adds. "It's just jam-packed with in- credibly amazing characters and shots. Chris Columbus allowed us an amazing freedom to contribute creatively to this project, and these facilities did great work." Although the ambitious CG characters will likely have the biggest impact on audi- ences, visual effects artists will more likely remember the creative application of fluid simulations and the seamless work. Not to mention the fact that these artists produced all these effects in less than a year. n Barbara Robertson is an award-winning writer and a contributing editor for Computer Graphics World. She can be reached at BarbaraRR@comcast.net. Going to Hell When director Chris Columbus asked visual effects supervisor Kevin Mack to brainstorm some ideas for a sequence in which Percy Jackson goes to the under- world, Mack created a drawing on a marker board of Los Angeles with chasms. "The idea was that as they'd fly in a boat to the underworld, they'd pass by all this personal stuff—hats, wallets, diplomas, old photographs, walkers, guitars, and so on," Mack says. "I did a huge drawing, and Chris loved it. And then before anyone could photograph it, someone erased it to put up the new schedule." With Mack's idea in mind, Pixomondo developed previs and then created the shot using 3D matte paintings, CG objects, and photographs. The crew filmed the actors in a boat dangling from a crane on a hydraulic rig. "We went to a prop house in Vancouver and shot tons and tons of things from a ll periods," Mack says, "cell phones, old typewriters . . . it all floats in a kind of river in the sky. As Percy passes through it, he grabs a pocket watch. When he looks down, he sees thousands of lost souls on pillars or rocks, and one pillar in the middle with Hades' mansion on it modeled after the Hearst Castle. The dock at the mansion and the doorway façade is a set. The rest is all-CG." –B. Robertson Luma fastened the snakes onto Uma Thurman's head and animated the creatures as if they represented Medusa's multiple personalities. They adore Medusa, caress her, and rub her cheeks, but when she decides she wants them to turn someone to stone, they rear into a synchronized performance.