Issue link: https://digital.copcomm.com/i/65907
Simulation n n n n ent ways. Spray turns into mist, lands on the water, and turns into foam." The goal for the new system was to stream- line the workflow and, at the same time, make the water simulation more accurate. To do this, the developers decided to split the sim into two parts. One part, the base simulation, would, as before, create the surface and, with some secret sauce overlaid on that simulation, the splashes. A second group of sims driven from the base water splashes would create the spray, mist, and foam. "We had used the base particle-level set method that Stanford pioneered for years," Hankins says, "long enough to be clear about the difficulties we always had in production. So, we added another layer to it that helped us achieve splashy structures out of the box." The base simulation might typically run in- side a virtual 1,000 x 2,000-foot cube, with a grid dividing the volume into two-foot-square cells. An artist inserts geometry representing ships or other elements into the volume and sets the fluid in motion by specifying such parameters as wind and velocity. As the fluid moves through the cells in the volume, the simulator derives an implicit surface. Now, in addition, a particle-based fluid simulation cou- pled to the base simulation kicked in when the grid was too large to create detailed splashes. "Basically, the system knows when the "So, in that sense, it's not new. What's new is how we were able to smoothly and seamlessly blend these particles into the underlying base- level set. The way we did the dynamics gives them a nice splashy structure so the artists didn't have to spend a long time to get a good look. It worked out of the box, but they still had controls." Controls affected such charac- teristics as how loose or tight a splash would be, how big or small, or how clumpy. The second part of the simulation generat- ed spray, mist, and foam: The splash particles emitted spray particles, and when the spray particles fell on a surface, they generated foam. "We set up the pipeline to do it automatically, but we didn't run it as a single simulation," Hankins says. "An artist would typically work with a low particle count, a few million may- be, to figure out if the motion and the balance between spray and mist were correct, and if it needed additional forces. "It was something they could turn around quickly at a work- station. But for rendering, we' level of detail with, say, 300 million particles on eight to 12 [eight-core] machines. It was a d crank up the trivial parallel problem because the machines could work independently." In addition, the artists ran separate simula- tions of the air around the water and coupled that to the base water simulation to produce swirls and eddies. One of those artists was Hankins. "This was the first time I've been able to be on a film from the beginning of R&D all the way through production," he says. "Mostly we do R&D and then pass on our work to production. Being able to see something through to the end was awesome." At the end of this process, the datasets were so big that the previous system, which figured out which cells contained fluid and generated a mesh surface for rendering, bogged down. "We had to rewrite the mesh-generation part of the rendering system, as well," Geiger says. "But, actually, it uses the same idea. Rick [Hankins] said, 'Instead of having one huge grid, let's dynamically build as many small grids as we need. We can build the surface in tiny, tiny parts relative to the whole thing, and then stitch them together.' It was more work because we had to stitch all these small parts Supervising the Show Grady Cofer and Pablo Helman shared the job of supervising the visual effects under lying implicit surface is under-resolved," Hankins says, "that is, when the grid can't capture the detail the simulation requires. We identify that and generate new particles to fill in the missing detail." These new splash particles are fluid solvers in their own right, with dynamics governed by an optimized system the team developed spe- cifically for this purpose. They can have their own velocities. They're fast. And they can af- fect the underlying surface, as well. "The key realization was that the water in a simulation needs to know about its surround- ings," Geiger says, "the bits of water near to it. But, it doesn't need to know about the water miles away. So, rather than taking a huge grid and subdividing it, the system dynamically builds little grids, sometimes thousands of little grids, exactly where we need them. The small grids can have whatever resolution we want. We would get down to features a few inches in size." That gave Geiger the detail he had asked for. And, because the splashes were part of the base simulation, they were correct. Cross off precise and accurate, too. "This is all very similar to the way the par- ticle-level set naturally works," Hankins says. for Battleship. Cofer was involved from the start in 2009 when director Peter Berg pitched the idea to Industrial Light & Magic. Helman joined the crew later, after he finished work on Airbender. All told, the film had 1500 visual effects shots, with ILM creating the majority. In addition to a crew of 250 at ILM, the supervisors and Animation Director Glen McIntosh oversaw work from three other studios: Image-Engine, the Embassy, and Scanline. The effects consisted of the water simulation, creature animation, ships, and destruction. The creatures were linebacker-sized humanoid aliens but with four fingers spread around their hands like a claw; they usually appeared wearing a full suit of armor. "Peter Berg was the right director for this project," Helman says. "He loves football and he loves the Navy. When you put that together with the energy he has, you get an action movie, and action movies are difficult. It isn't just about quick cuts. It's about the story and caring about the characters that are fighting." Both Cofer and Helman spent time with the Navy, filming from boats and helicopters during the semi-annual RIMPAC naval exercises near Hawaii in June 2010, during which 32 ships, five submarines, 170 aircraft, and 20,000 person- nel from 14 countries spent a month carrying out maritime operations that even included the sinking of ships. During that month, Cofer was on a destroyer for 10 days, while Helman filmed from boats out of Pearl Harbor and from helicopters. "It was great," Helman says. "We could internalize how big the ocean is, the huge- ness of those ships, and how hard it is to maneuver them." Footage filmed during RIMPAC became a source for background plates, textures, and reference. Back at ILM, Cofer and Helman worked in adjoining offices, and both, hav- ing moved into their roles as visual effects supervisors from digital compositing, reviewed and fixed shots on Autodesk Inferno systems. "We share the same aes- thetic," Helman says. "We'd look at a shot and point to the same things. We'd put in camera moves, lens flares. It's easier than giving notes." –Barbara Robertson April/May 2012 15