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Prince of Persia: The Sands of Time owes as much to The Matrix as anything else because it required a variation of the famed "bullet time" for its signature rewind through time effect with the magical dagger.

Thus, while Framestore created vipers and huge quantities of sand, MPC worked on the CG Alamut City and used ALICE to simulate the Persian attack and Cinesite got the Royal City of Nasaf and Avrat bazaar chase, Double Negative focused on the rewind effect.

This included the final Sandglass Chamber that is effectively a mammoth rewind, incorporating flowing, magical sand, glowing figure and rewind images -- all in a very nearly fully CG environment of photoreal rocks cascading and crumbling from the walls, according to Tom Wood, the overall visual effects supervisor.

"The rewind sequences were Dneg's biggest challenge," Wood suggests. "Using their proprietary 'event capture' software to carve a 3D version of a scene, captured with up to nine Arri 435 cameras slaved together shooting at 48fps with a 90º shutter. We renamed the traditional 'bullet time' to 'dagger time,' as we were now able to place a camera anywhere along the path of the original camera layout, at any time. We could run forwards and/or backwards at any time: meaning we could see all time at any place. This meant we could create a full motion long exposure effect that we could travel past or through. The idea was for the rewinding character, visible within their extended long exposure, to reverse through their own path, dissipating it through simulated fluid turbulence created by their own body motion.

"The 'ghost' figure was established to be an external viewer, reacting with the audience to the rewind. Initially the approach to the treatment was simple, but as Dneg demonstrated more of their fluid sims, he became more complicated. He ended up being a fully CG figure, roto-animated over the cast's performance, with a projection of the facial performance. Sand swirls and blows around and from the 'ghost' in Dneg's fluid sims."

Overall, there are four rewind sequences consisting of 200 shots, which took Dneg 18 months to complete. According to Mike Ellis, Dneg's visual effects supervisor, there were three main objectives: detach the viewers so they could experience the rewind (the "ghost" effect), the need to see people reverse in a magical way (the "rewind" effect) and the need to change the whole environment to distinguish between rewinding and regular forward action. Not only that, but the same actor would need to appear twice in many shots moving both forward and in reverse simultaneously with two distinctly different looks, requiring the need to freeze and rewind some aspects of the same shot and a certain amount of relighting.