The actors – Robert Downey Jr. and Jared Harris – were filmed for the sequence using a technique that is becoming increasingly popular with VFX teams. They were attached through harnesses to two gigantic KUKA robot arms. More commonly used for making cars and the like, these powerful arms can be programmed to move – to puppeteer, almost – the actors through space. Whilst offering great benefits in terms of precision positioning and performance capture from the actors, this technique does have its downside. “There was an enormous quantity of clean-up work to be done before the actors were ready to be placed in the shots,” says McCulloch, “We had an eight-strong paint and roto team putting in long hours for many weeks to remove all traces of the harnesses and the arms, as well as patching up various bits of the outfits with CG elements.” This action was shot on a Phantom HD Gold camera, which can go up to 1000fps, though 432fps proved the ideal speed for the central slo-mo section.

Unsurprisingly, the water itself was the biggest headache. Ben White was Framestore’s CG Supervisor for the project. “Several factors made this water more difficult than usual,” he says, “Waterfalls do not lend themselves brilliantly to fluid simulation software, which is at its best on rivers and seas – things with a surface. Also, the fact that it was such a long waterfall meant that we were dealing with colossal amounts of data, because we had to have pre-roll for the entire kilometre, and when you factor in the time-warp down to almost 500fps in the middle of the shot, and the fact that the camera is pointing straight up into the descending water, making it simply hard to see - all this meant we had our work cut out. In the end we broke up the water into several segments rather than trying to do it in one piece, with each segment being made of multiple layers to achieve the complexity we needed. We had a team working in Naiad, on the water coming down from above, and we had another team working in Houdini providing a different element for the lower part of the waterfall where it blends in to the live action elements. We also added CG and live action elements of water vapour and mist being pulled away from the surface which helped to give a special relationship to the falling actors in this huge space. The live action elements were most successfully used when we’re looking straight down at the end, because essentially the camera’s locked off, so the photographed element worked well there.”

Another water element proved more readily susceptible to technological augmentation. As the protagonists pass the camera in close-up, Jarrett and Ritchie wanted to see water droplets in motion around their heads. The compositing team found that the latest version of Nuke (released just in time to help out) gave them a set of tools that helped them sidestep a 3D solution. “We found some photos of live action water droplets from reference libraries,” recalls Quintavalle, “And we put them onto cards – lots of droplets arranged in motion and distributed as we wanted. It was a temporary measure at first, while we waited for the ‘proper’ particles to get rendered. Then as it went along we thought, ‘Could we make them move a bit as well, add a bit of warping? Could we have a bit of refraction as you’re looking through them? Can we get the time-warp working properly?’ and each time the answer was yes. The drops just kept getting better within Nuke until we realised that we actually had the shot we needed.”

Half of Framestore’s 30-strong Shadows compositing team worked on this one sequence. It was one of the first to be started in October 2010, and among the last to be finished. It was a labour of love, blood, sweat, tears and 28 terabytes of data caches, and the team are justly proud of the finished result.

* * * Spoilers End * * *

Trained Assassins
The other key sequence that Framestore created for Shadows takes place on a train speeding through nighttime countryside. A band of assassins, disguised as British soldiers, has boarded the train and plan on dispatching Holmes and Watson in a tornado of gunfire. Needless to say, our heroes are up to the challenge and explosively foil their adversaries.