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n n n n Virtual Environments Wood worked with a team at DNeg led by VFX supervisor Mike Ellis to design the effect, which takes place four times in the film. “A key component that [director] Mike Newell wanted early on was that anyone press- ing the button had to step out of body and look back at everything rewinding,” Ellis says. “Te actor had to be in two places in the frame, going forward and going backward. Tat made it complicated to shoot. And, Mike didn’t want just footage playing backward. He wanted it to be an effect linked to the dagger, and he wanted the whole environment to feel different.” To shoot the actors, Double Negative used an “event-capture” system that the studio had first experimented with for Quantum of Sol- ace, a next-gen evolution of the “bullet-time” technique used for Te Matrix. On set at Pinewood, the DNeg crew installed nine Arri Group Arriflex 435 film cameras equipped with identical lenses in a curve that roughly followed the path the actor would take, and then filmed the action at 48 frames per second (fps). Afterward, layout artists used propri- etary software to derive a smooth camera path through the scene. “We combine those cameras and cre- ate the entire shot as a CG version of itself,” Ellis explains, “the set, the background, the actors.” Tey separated the actors from the backgrounds, rotoscoping each for all nine cameras. Next, taking the rotoscope for all nine cameras, they created a basic cookie-cut- ter form in 3D space, a mesh for each actor in the shot. Using a second process, the crew shrink-wrapped that basic form into one with higher detail by comparing motion vectors be- tween different cameras. Te result was a more accurate mesh of the actor. To apply the pho- tographic textures to the mesh, layout artists tracked the parts that needed to look photoreal in a shot. Ten, they broke the CG character into particles by giving the particles a geom- etry target and then applying the appropriate photographic textures to the particles. When Dastan presses the button on the dagger, magical, moving sand bursts from his body. Te camera then looks through his eyes at himself moving backward in time. A slight sand trail follows. “Because we had the real- world photographic elements from the nine cameras and had all these angles around the actors, we could use the textures on the par- ticles even when the characters are breaking up,” Ellis says. Moving the particles through the studio’s DNeg Squirt fluid-dynamics sys- tem added the magical motion. Squirt also played a role in shots that DNeg created for the finale. During a big confronta- 12 June 2010 At top, Double Negative created a time-rewind effect by filming the action with nine cameras, extract- ing the actors, and swirling magical, light-emitting sand. At bottom, Framestore emptied a room filled with sand and sent the hero sliding down a particle avalanche. tion, the magical, light-emitting sands of time pour out of a 300-foot-high crystal. “We had to treat the sand as a character with a life of its own,” Ellis says. “It barrels into everything, breaks down the cavern, bounces off walls. It’s a destructive force.” To create the sequence, the artists worked with layers, starting with the sand crashing to the wall, which triggered rigid-body simulations that crumbled the wall. “Te rocks that fell off the walls interplayed with the original sand elements, though, so we had to simulate the sand again,” Ellis says. “It was a circular thing.” The Sand Trap Getting to the crystal was half the fun for the Framestore artists, who built a huge, under- ground labyrinth and a trap room full of sand. When the surface of the trap room collapses, the actors slide down tons of digital sand. “It was a huge undertaking,” Wood says. “As the surface collapses, the sand flows away, revealing architecture that collapses and falls. So, Framestore took a pragmatic approach. Tey spent a long time developing software approaches so they didn’t have to render bil- lions of particles bouncing off one another. Tey didn’t make a room full of sand; they made it look like a room full of sand.” Te idea for the collapsing sand room origi- nated at Framestore. “We pitched it to the stu- dio a couple of weeks before we needed to film it,” says Ben Morris, visual effects supervisor. “We hardly had time to do storyboards. And, we thought it would take two to four weeks to film, but they gave us four days. It was the very last thing to shoot.” At first, they had Jake Gyllenhaal slide down a sloping sandpit built on set. “Jake was fantastic, but the sand got into people’s eyes, and resetting the sand was laborious,” Morris says. Moreover, the sand didn’t move and flow like it would in a collapsing sand room. So instead, they had Gyllenhaal slide down fiberboard slopes. Tat meant all the sand would be digital. “We tried to avoid creating one massive simulation that would take days and days to render,” Morris says. “And, we didn’t want a physics-based system that we couldn’t change. So we broke it down into smaller pieces, to control what was going on. In post-vis, we de- fined the surface shapes for the main body of sand and the architecture it revealed.” Effects artists created planes that represented all the shapes in the shot and sent particles flow- ing down the surfaces, to produce the main flows. Additional simulations layered on top sent particles surging when shapes collided. Shallow