Visual effects facility Motion Picture Company (MPC) was responsible for more than 450 shots for Marc Forster's blockbuster movie World War Z, which included some stunning action sequences, such as the thrilling plane crash and the nail-bitingly good zombie pyramid shot in Jerusalem.
The action in Israel starts in the safe area known as Busland. The shots were a mix of live-action plates, added CG environments, CG humans, CG zombies, CG helicopters and FX passes for dust and helicopter wash. Once Busland gets over run by zombies, the action continues throughout the city.
"The Jerusalem sequence was a great challenge!" says MPC VFX supervisor Jessica Norman.
"MPC created the zombie pyramid, crowds of zombies overturning a live-action bus, a sequence of shots of zombies running down narrow streets, a tentacle of zombies attacking helicopters, wide angle shots of Jerusalem with massive zombie crowds, hero zombie animation, CG planes and environment work."
MPC received concept art early on from Framestore, showing different zombie formations. CG supervisor Max Wood was in charge of the 3D work, and planned from very early on how MPC's teams should tackle these massive and complex crowd simulations.
"Some of [the concept art] showed zombies creating tentacle shapes, and another variation showed them appearing as a swarm of insects and schools of fish formations," explains Norman.
"Our animation supervisor Andy Jones also provided us with motion studies made with performers," she continues. "We used MPC's mocap room to capture clips of the different actions we needed for the pyramid, which included performers climbing up ramps and nets. Complex crowd shots started with the layout, shape and speed of the crowd being defined."
To create the hordes of zombies, MPC had to enhance its proprietary crowd system ALICE, which would usually be used to keep agents in the crowd apart, but here was used to simulate streams of CG zombies.
"For the pyramids we started with geometry that we then populated with clips based on inclination using ALICE, which enables our artists to manage crowd behaviour, motion clip editing and blending and customised scripting for large groups of agents," says Norman.
Many of the shots also required MPC to leverage the power of PAPI, its in-house rigid body dynamic solver based on the Havok engine. "PAPI and ALICE are bridged together, allowing us to create behaviours and animations in the crowd engine, which could then also be used to drive the physics simulations at the same time," Norman explains.
MPC's pipeline was adapted to be able to promote single ALICE agents to the animation department, then either keep them as a hero or incorporate them back into the crowd.
For the larger crowds, MPC used its in-house cloth solver that works with ALICE. "We used nCloth for hero cloth sims or where extra crowd cloth detail was needed," Norman explains.
"One of the biggest challenges for our lighting team was to render the crowds of zombies. The number of zombies made rendering tricky, as well as the fact that any zombie could start off in the distance but end up full-frame as they advance."
The lighting team worked closely with the crowd and cloth teams to ensure the right level of detail was used and to split up the crowds in ways which would allow them to render in the most efficient way without compromising the quality and look of the renders.
"Compositing supervisor Jonathan Knight and leads Lev Kolobov and Jeremy Sawyer worked closely with our lighting team and discussed the best ways to break down the many passes and layers that made up the crowd," says Norman.
"We then set up standardised Nuke templates that streamlined the compositing workflow. For the complex zombie shots, we rendered deep passes to allow us to combine the different layers of crowd more easily. Many live-action elements of smoke and dust were then added to help integration."
FREE talk: Meet MPC and learn their secrets!
On 18 October at London's MPC's global head of crowd, Adam Davis will present the creative and technical processes behind the VFX of World War Z, demonstrating how the team took early concepts through to completion on their most challenging crowd show to date. The event is free - you just need to register here.