Issue link: http://digital.copcomm.com/i/1039130
www.postmagazine.com 29 POST OCTOBER 2018 Rocky Mountain High While the film underwent the initial revisions, Kirkpatrick and his team were unable to hone in on the specific environments until later on in production. As a solution, the group first started building set pieces they knew would exist in this world — which would be snowy, icy and rocky. They also knew there would be a yeti mountain and a human city. Everything else was done on the fly as the environmental artists received se- quences from the story department. The big environment (literally) is yeti mountain. The modelers began by building the outside of the mountain and all the pieces that would later be used to construct the yeti village. From those kit pieces, the group could make just about any other environment that was needed, including the human world — changing proportions, of course. "We had never really done any procedural texturing on the fly at render time in any of our prior movies," says Herbst. "But for this film, we developed a new set of tools that ran on top of some of our other existing tools to leverage that procedural texturing." 'Snow Joke Just as hair/fur is a notoriously difficult element for animators, so, too, is water in all its forms, and in the land of the yeti, there is plenty of ice and snow; three types of snow, in fact: falling snow, surface snow and effects kicked up by active feet. But blanketing the entire environment in freshly fallen snow is time-consuming if done by hand. "None of the ice and snow, even on ledges, is hand painted. All of it is created procedurally," explains Herbst. This allowed the team to inter- change set pieces at any given moment or even swap ice to rock, or rock to snow, easily. Initially, the effects artists produced a simu- lation of a snowfall with wind direction, let the snow accumulate and then restructured the set and skinned the results. But that turned out to be costly and complicated. "Theo Vandernoot, head of the effects team, suggested we just do an ambient occlusion process instead, and still have a wind direction associated with it to break up the snow and give us drifts," says Herbst. This new snow-padding system works within Houdini and contains tools for accumulating large swaths of snow into any environment, based on programmed variables such as wind direction, amount of snowfall and relative stickiness of the objects to be coated, thereby varying the look throughout the movie. "It gave us flexibility," notes Herbst. "We didn't have to remodel the snow again; by dropping it in and letting it accumulate, we could move objects around and control the amount of snow in each shot." In addition, the effects team used a few differ- ent systems to tackle interaction with the snow. For footprints, they used a displacement system that took historical data of a character's feet in a shot and interpolated that back out of the shot and across a sequence. It would displace at ren- der time and add bits of granular chunks of snow around the edges of the displacement as to not appear smooth and perfect. The group also devised new system, called Katyusha, that offers artists a more efficient way of producing high-resolution granular snow by combining a rigid-body destruction system with a fluids solver. Its name comes from doing each step of the process in small chunks versus a sin- gle, large simulation. "Katyusha lets us do a colli- sion rigid-body simulation that breaks up all these chunks that stay stuck together or tumble and break off into a subsequent number of smaller chunks, or even eventually kind of collapse back into flakes of snow," explains Herbst. Rather than rendering this type of snow as geometry, Imageworks rendered it as a volume for a few reasons. First, if left as chunks, the snow looked more like ice because of the rigid, sharp edges. Also, the volume enabled the light to transport through it better, so the crew could mix and match the various types of snow and render it together in the same light. Evolutionary Tale In Smallfoot, Migo and his friends have to go "off path" as they search for new beliefs. In a way, the same can be said of the team at Imageworks, as they ventured from some of their previous method- ologies in search of better, more efficient ways to approach their latest project. Their trek was not always easy, but in the end, they conquered a mountain of technical issues, including those for creating hair and snow. But here, as in many film projects, big steps are just as groundbreaking as small ones in the quest to leave a lasting footprint. Karen Moltenbrey is the chief editor of CGW. Imageworks created three types of snow for the film: falling snow, surface snow and effects related to the snow.