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www.postmagazine.com 26 POST JULY 2016 Summer B L O C K B U S T E R S colors, the team wanted to mimic how these changes happen in the real world. "We wanted it to look natural and not like a cross-fade," says Jeremie Talbot, character supervisor. "Our artists wanted to do something similar in the computer to what happens on a cellular level on animals." Simply put, the artists manipulate many circles, dots if you will, that create a texture with changing colors over Hank's body. "When we combined that with noise, we got a naturalistic effect," Talbot says. "Hank could match a background or a supplied painting." Finding a way to make that work took the team two years. Creating Hank's shifting shapes fell largely to the animators, but with new tools and sophisticated rigs making it possible. Even so, a shot of Hank sliding into an aquarium, for example, took six months for the animators to do. "That's how hard it was to animate this character," says Mike Stocker, one of two supervising animators on the show. "We had two challenges. Getting all those suckers moving, and getting a rolling feeling for the tentacles. The muscle starts from the body and works to the tip, and that rolling feeling was something we wanted. Jeremie [Talbot] made a super complicated rig. We could use a 'grab cylinder' that I called the elbow. We had to lead with the elbow, not the end of the tentacle, to get an octopus feel." Another tool within Presto, Pixar's proprietary animation system, gave the animators a starting point. "We could draw a tentacle and snap the model to the drawing," Stocker says. "That got us 60 percent of the way. Then, we polished the pose." Talbot's character department created the rig that animators used to pose Hank and his seven tentacles. One of the first reference videos Talbot looked at to de- termine how an octopus would move was of a mutable creature sliding into a bottle. "It terrified me," he says. "Not the look, but how it moved over a rough surface; the way the flesh rolled." First, the team created a control that animators could use to set the depth of the webbing between the tentacles, and developed a new curve function. "After a lot of work, we had some- thing for animation to play with," Talbot says. "But, we didn't have the sliding motion we needed." For that, the rigging crew turned to the simulation department for help. There are 350 suckers on Hank's tenta- cles, and each sucker needed to squish, stick and pull away in a believable man- ner. Solid mechanics came to the rescue. "There's a whole branch of engineering that, given a force applied to an object, asks how are all the points in that object moved, displaced and stressed," says John Halsted, supervising technical director. "We borrowed approaches from that field of science to figure out how Hank moves." Thus, each of Hank's suckers has a little tetrahedral mesh that provides input into a customized simulator. The simulator produces the squashing and sticking; it deforms the little sucker based on applied forces. "The simulator is a heavily custom- ized version of Physbam," Halsted says. "It uses finite-element analysis (FEA) to have a solid, elastic material behave like muscles or flesh. We use the tetrahedral mesh to do the volume-based jiggle and solve it with FEA. To get the skin sliding, we used a triangle mesh over his body." Once the team managed to create one sucker that would squish, stick and pull away, they could propagate the method to all the suckers. Then, they needed to make the tentacles look soft and fleshy as it squished along. "A separate skin simulation allowed the skin to move along the same plane as the outer surface of the body," Hank the octopus was a challenge on many levels, including move- ment, color and skin.