Issue link: http://digital.copcomm.com/i/1039130
www.postmagazine.com 28 POST OCTOBER 2018 compositing was done in Foundry's Nuke. As for the generic yetis (and humans) in the film, the team developed a mix-and-match process using the studio's Kami geometry instance system, where- by procedurals could be layered on top of the hair at render time. As Herbst explains, the yetis had one basic body shape that was stretched to make other shapes. And, they would have different base hair grooms — short hair or long hair for the arms, legs and mid-torso, while the shoulder area comprised one of three shapes (U, V, or an arc). Using the pro- cedurals varied the look at render time to define the hair as being curly, wavy or silky. Adding horns, head hair and beards helped create the entire yeti village. Hairy Beasts One of the most difficult elements to animate in CG is hair, and in this film, the majority of the characters are covered in thick fur. For several years, Imageworks had successfully tackled hair and fur using its legacy pipeline. However, when the crew assessed the huge amount in this film, Herbst, along with look-dev lead Nicki Lavender and head of effects Henrik Karlsson, began look- ing for a new, more efficient solution in terms of simulation and, especially, shaders. "It was limiting the resolution of how fine and silky you could make the hair look, and simulta- neously it was overdriving opacity in a ray tracer, which shot our rendering times through the roof when we were trying to make it do more than it had done in the past," says Herbst. So, they created a new hair-shading system specifically for animal hair, that used a multi-scat- tering approach. Instead of ribbons that looked like clumps of hair, they now had individual strands, resulting in much higher fidelity in terms of detail and qualities, like texture and softness, for a wider range of hair/fur types. And, by making the hairs truly opaque and writing the new shader so it could transport light and prevent the shadows from becoming too dense within the hair volume, the rays now do not penetrate deep into the vol- ume, enabling the artists to add more hair. Without question, the amount of hair on each yeti is impressive. Migo alone has 3.2 million individual strands of hair, while Meechee and Fleem have 2.5 million each, Kolka has five million, the robed Stonekeeper sports 1.3 million and the curly-haired Gwangi has a whopping nine million (of which 3,000 are simulation hairs). On the simulation side, Karlsson and his team developed layers of tools that worked inside the Maya Nucleus solver to drive the control hairs. The studio's plug-in to its version of Arnold, called Kami, then took that information and generated the hair on the fly at render time and deformed it on the fly as well. When the team started the film, the studio was still working on new developments within the Arnold renderer, one of the biggest being adaptive sampling that refocuses rays within a ray tracer where needed. "That was a huge plus for us. If we did it the old way, the render times would have been through the roof, resulting in hundreds of hours," says Herbst. Another development enabled lighters to pick up from where they left off when moving from a mid-level render with a lower anti-alias setting (to get a feel for the lighting) to a higher-res frame. "If that medium-quality version had already burned 20 to 30 hours of clock time, you didn't have to lose that. It would just start from there and keep going upward." Heart Of Stone Herbst believes that one of the most diffi- cult characters to create for Smallfoot was Stonekeeper. "One of the worst things to do in any animation pipeline is circle back in the middle to finish a character, and, unfortunately, that was really the only way we could solve Stonekeeper's requirements," he says. Stonekeeper is a hairy character who wears a robe of stones. He also has head hair that is very long, with layers of braids, and a long, braided beard. "The pipeline here went through animation, into our character effects team to simulate a cloth patch of what would be underlying the stone so it felt more like a robe — a really heavy robe," says Herbst. "Then that would go to our effects team. While our effects team was working with that robe, adding the stones, the character effects team was actually starting the hair simulations, to get those moving." The effects department would do a rigid-body collision simulation for the stones on the robe. Once that was approved, the character effects team would merge the layers together and finish the final simulations for the hair. If something was not working in terms of performance, then the model would be sent back to animation and the process would begin again. The characters' thick fur presented a particular challenge for animators, so they created a new hair-shading system geared especially for animal hair.