Developing Drop
Jan 12, 2010 12:00 PM, By Ellen Wolff
How Digital Domain arrived at a new simulation system.
Before and after skyscraper collapse from 2012.
Software tools for visual effects include such hall-of-fame names as Autodesk Maya, Side Effects Software Houdini, and Pixar RenderMan, but with each passing year, VFX studios worldwide are expanding the standard toolkit to meet increasingly ambitious production challenges. A recent case was Digital Domain (DD) in Venice, Calif., which was tasked with demolishing Los Angeles for director Roland Emmerich's apocalyptic 2012. The software team at DD knew that conventional methods previously used for simulating rigid body destruction in Houdini would be insufficient to handle the scale of disaster that Emmerich envisioned. The number of collapsing buildings was too large, and the director wanted the freedom to direct how the simulations appeared to camera. DD would need to come up with a more efficient and flexible method—and do it fast.
"We may have had about three or four weeks," says Nafees Bin Zafar, a software engineer with nine years of experience at Digital Domain who worked on Pirates of the Caribbean: At World's End as well as 2012. Zafar, who is now at Dreamworks Animation, had previously earned a Scientific and Engineering Award from the Academy for DD's fluid-simulation software, so he was as prepared as anyone could be for developing a new sim strategy on deadline. "We had a team of engineers and artists that had worked together before," he says, "so we had confidence. We had a good sense of how to build artistic controls on top of the math. That impacts workflow, and how the software appears to users."
While DD's expertise with water simulation provided some precedent, Zafar says, "The math of rigid-body sims tends to behave closer to reality than water-sim math does. With rigid-body sims, if you have a reasonably sized object and it falls at a real-world rate, it's a little more forgiving. Rigid-body sims look more like traditional animation."
Along with Zafar and his fellow Sci-Tech winner Ryo Sakaguchi, DD's development team included Michael Clive, Ken Museth, Ramprasad Sampath, and Marten Larsson. Computer Graphics Supervisor David Stephens, who had just joined DD from Sony Pictures Imageworks, was also a key player. He had overseen destruction scenes at Sony for Watchmen, so he understood the challenges presented by 2012.
Rather than try and invent a new approach from scratch, the DD team considered building on videogame technologies such as Havok and Nvidia PhysX.
The studio had previously used the Unreal Technology game engine for commercial productions, so there was some familiarity. Stephens notes that more and more software companies are heading in the direction of using game physics, citing tools such as RayFire. But DD ultimately settled on using the open-source physics library called Bullet as a foundation for its rigid body simulation approach. The team then added techniques for shattering objects that were made of varying materials, such as wood or glass.
"It's been our experience that open-source projects help a lot," Zafar says. "Because typically in feature effects we end up needing to work very differently than the original intentions behind libraries that were built for games."
Using Bullet as a foundation proved to be a savvy choice. "When we ran into conceptual problems or didn't know how to get something done, we posted questions to the Bullet user group," Clive says. "People knew that we were incorporating Bullet into a Houdini-based pipeline for film effects. Usually we got feedback, including from the author of Bullet, Erwin Coumans, who's become a good friend of ours."
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