Issue link: https://digital.copcomm.com/i/77744
VFX•CG Films n n n n be achieved by first simulating a flat surface for the hair to ride on, and then simulating the hair on top of that as a second pass," says Maxwell. The group faced a similar issue to Granny's neck jiggle for Flynn, a blubbery seal, who had to look as though he had underlying fat as he bobbled around on land and on the ship. "Flynn was our first character with fat simu- lation," says Maxwell. The trick was to give him believable, wobbly blubber and retain his mass. When faced with large voxel volumes, the effects department devised two different tools that could be used: one that contracted the simulation grid in areas that were either ob- scured by geometry or the fluid simulation it- self, and another that optimized the sim based on the camera pixel size. Schneider explains how it worked: "A large destruction sequence called for dust to emit from rigid-body simulations of collapsing for- mations of rock and ice. Our fluid simulations were fed by voxel fields, which were generated at the moment of fracture from the interior faces of the fractured geometry used in the rigid-body simulation." Any data that was not necessary for the render was excluded, making the information more manageable. In addition, the group made improvements Maurer. To get more interactivity for the pine trees, the team moved from a sprite-based so- lution to one involving voxelized fur for the pine needles. This enabled the artists to easily generate particles for snow on the trees, which were then meshed and rendered as subdivision surfaces. In the past, they had hand-modeled snow clumps onto the NURBS sheets. to the voxel storage format for SMOGVOX, a volumetric procedure developed by Trevor Thomson in Blue Sky's R&D department, so that it was lighter and easier to manipulate. One shot in particular mixed 12 volumes of mist, rock, dust, and ice dust, for a total of 1.2 billion voxels, and rendered in less than an hour per frame using 10gb of RAM. Voxel technology was used for characters (mainly fur) and vegetation, as well. Accord- ing to Eric Maurer, fur and procedural model- ing supervisor, there were significant updates with the voxel and fur technology between this film and the third movie in the series, Dawn of the Dinosaurs (2009), most of which was developed for Rio (2011). While the group has been voxelizing ge- ometry for grass since Ice Age 2, after the third film, Sean Palmer, formerly in R&D and now in fur, developed the ability to voxelize the ma- terials on the geometry, allowing for a more generalized implementation. "We used voxels for all the foliage on all the trees, and would often voxelize all the set dressing, typically using less RAM than we would have with traditional geometry," says New Characters Historically, the Ice Age characters have pre- sented a fair share of hair and fur challenges. For this movie, the character simulation group had to develop solutions for some of the new characters with longer hair: Granny's shawl, Peaches' hair, and Gutt's beard. And that wasn't all. Granny, a wrinkly old sloth, has a neck that jiggles when she moves. At first, the team ap- proached this with a combination of model- ing, materials, and rigging. Not quite satisfied with the performance they were getting, the group then developed a technique that en- abled the animators to get the look most of the way there, and then completed it using simulation for the character's waddle and for the desired wrinkle on her skin. Collaborat- ing with rigging and modeling, the character simulation team also simulated the thin skin of the elderly sloth using a high-resolution mesh sock. "Granny was the most complex character for us, as she included all of our character simulation war chest in one character: cloth, skin, fur," says Dylan Maxwell, character sim- ulation TD. "She had a floppy waddle, which was simulated as loose skin." To make things even more interesting, Granny wears a shawl of fur. As a result, the group had to develop a pipeline and tool set to accommodate the workflow between ani- mation, character sim, and the fur/procedural modeling groups. "She had a loose shawl of matted hair on her back, which could only A character simulation rig was designed so that the animators could work with a fast, optimized rig, and then utilize a simulation to add the high-frequency ripples that occur on seal blubber as the animal propels itself and collides with its environment, says Keith Stichweh, character simulation supervisor. Because animators are usually not restricted by the laws of physics, they had to rethink how they would attack a shot and consider how character simulation would affect the final animation. "[Flynn] introduced a whole new interaction with animation, wherein the ani- mators had to restrain their instincts to hand- animate the fat, and at the same time, give poses that accentuated the as-yet non-existent simulated jiggle," Maxwell adds. Gutt, the orangutan, was quite active in the movie, and as he moved, so, too did his dread- lock beard, swinging to and fro. The character simulation team handled the beard, while the rest of his fur was created with voxels. "Gutt's groom presented our first long-hair sim. It was dangling and colliding with everything and everyone while he made insane swashbuckling ape movements," says Maxwell. Peaches' hairdo was challenging as well, because she used her hair as a prop when act- ing—just as teen girls often do. "We had to give her the looseness for wild motions and for disheveled movements, and the tightness to hold her style the way the design team envi- sioned this self-conscious teen," says Maxwell. While Peaches' simulations were not visually stunning in many shots, they contributed to the tension and drama more so than any other characters, he adds. Indeed, a number of the characters in Ice Age are high-strung and create their share of comedic drama, and that's what makes this se- ries such a delight. None, perhaps, more than Scrat, whose antics in a parallel story set the tone for this movie, which is sure to melt view- ers' hearts yet again. n Karen Moltenbrey is the chief editor of Computer Graphics World. June/July 2012 63