Issue link: https://digital.copcomm.com/i/759864
10 cgw n o v e m b e r . d e c e m b e r 2 0 1 6 "It's a two-character shot of Moana and Maui on the boat, seemingly an acting shot," he says. "But we talked about how we could execute the effects in that shot for a half an hour. Because of where they are, it was complex. We start with them dry, and then they get wet. They're on a boat. They're next to water. They interact with the water." In addition to various forms of water, Driskill lists hair, cloth, feathers, vegeta- tion, environmental effects like footsteps in sand, smoke effects, fire, and lava as the main challenges. Head of Effects Marlon West adds magical elements to the list. "Everything we would have asked them to avoid was added to the story, and we had to tackle it," Odermatt says. HAIR Both hero characters have long, curly hair that's oen wet, underwater, or blown about by the wind. And, the teenager Moana plays with her hair. Artists used an evolution of the proprietary soware Tonic, developed for Tangled, to specify an initial groom, and the simulation team developed a new system for controlling the hair. "We needed more control," Driskill says. "So we started on a big project and took it further than we thought we would." To develop the characters' hairstyles, look development artists (rather than model- ers) using Tonic would place tubes on a character's head and specify parameters. Based on those parameters, XGen, a geome- try instancer developed at Disney and now available as a plug-in to Autodesk's Maya, would populate the border of each tube, a shell of curves, with thousands of primitives. "The tubes give us a quick visualization and were good for authoring," says Simula- tion Supervisor Marc Thyng. "But they have drawbacks. We had so much volume, we started using a new object type in Maya to handle lots of curves." As for the simulation engine that drives the movement of the hair, the team devel- oped a new system based on what they call "Disney elastic rods." Thyng explains: "It was important for the curls to hold their twist and have springi- ness. For Rapunzel, we had used a mass spring model. For this film, we started with a discrete elastic rod model to do twists. Our smart guys here found ways to speed up the simulations so we could do fast iterations." With simulations taking as little as 10 seconds per frame, the artists could show the supervisors and directors results quickly and use notes in the form of "draw-overs" to make changes. "We're using real physics, but we cheat with forces to get 'Disney hair,'" Thyng says. "Generally, the hair wants to pull back to its rest shape. Before, we had constraints that held the hair in place. That was good for art direction, but the hair pulled back in an un- natural way. Now, the hair can move freely. If there is a lot of action, it doesn't always come back to the initial groom. It can be held in a messy kind of look in a pretty good way. That was a big deal." For example, when Moana bends down, her hair falls forward. Then when she stands, it comes back to a pleasing new shape and stays in that shape. Also providing challenges for the simu- lation artists was that Auli'i Cravalho, the teenage actor who voiced Moana, fiddles with her hair, and the animators wanted Moana to do that, as well. For example, "We wanted Moana to be able to take the hair from one side of her head, pull it over to the other side, and have it land in position," Thyng says. "We needed constraints to control the strength of the forces through timing and distance. So, we revamped our collision model and came up with new dynamic constraints." And now Moana can even slide her hair through her fingers. To make it easier for others in the pipeline to control the characters' hair, the simula- tion department provided a general setting COMPLEX VEGETATION, WATER, LONG HAIR, AND MULTI-LAYERED COSTUMES REQUIRED MASSIVE AMOUNTS OF PROCESSING TIME.