Paul Kanyuk on Pixar crowd simulation techniques at FMX 2012
The Pixar lead technical director reveals how crowds were created for Cars, Toy Story 3, Up and Ratatouille
Today and tomorrow, 3D World is at FMX 2012 in Stuttgart. Visit 3dworldmag.com to stay in touch with the conference as it unfolds, with coverage of presentations from the industry’s key figures and a flavour of what it’s like to visit Europe’s leading CG conference.
I’m back in the Gewerkschafthaus for Pixar lead TD Paul Kanyuk, who’s going to take us through the various crowd simulation techniques the company has used over the years. Crowds are important, he says, because they provide spectacle, make worlds more realistic and provide reaction to the character’s action. But they’re also hard to do – “so unless you come up with some technical tricks, you’re doomed”.
For years, Pixar has used two crowd teams: TDs for planning and broad generation, and animators for shot work and fixes. The animators “are the eyes of the audience” – they review the TDs’ work to make sure everything works on screen.
In A Bug’s Life, crowds were Finite State Machines: individuals reacted to events around and triggered set motion clips. Many games use a similar technique. The first tool was called Fred.
Cars was the first film after Bug’s Life to use large crowds. Fred was updated to Barney, establishing an internaal naming scheme for crowd tools based on The Flintstones.
Barney used transition states: walk then stand, for example. But transitions could get complicated, as in the Mexican Wave sequences in Cars. Transitions would respond to triggers.
Kanyuk explains that the cars in crowds were shaped using displacement maps to save on polygons.
A new crowd pipeline was created for Ratatouille, with hundreds of rats in some scenes. Here, crowds have to behave in different ways and often appear in the foreground.
The pipeline was based on Massive, which created agents that have instructions telling them how to react.
The system evolved for Wall-E to allow Pixar to support classes, so character types could behave differently. The robots were made to wobble in different ways, for example. Improvements were also made to agents’ anticipation so they felt more natural.
Pixar created what Kanyuk calls “brain springs” to manage how robots stopped: physics filters to make the robots wobble as they stopped.
Up used the same pipeline as Ratatouille because the only crowd, a pack of dogs, was relatively small and simple to control. They rarely go back to use a previous tool version, but this was an exception.
The scene in Toy Story 3 where the heroes are welcomed to their new home was done with “brute force” – individual rigs for each character. “Sometimes you just gotta animate it.”
For Cars 2, Pixar evolved the ‘shrinkwrap’ displacement map system, with 12 shader maps rather than three. Masks in the shader maps were used to animate eye and mouth movement, saving a lot of data storage. The system is fine for cars, but wouldn’t work for humans.
Designs where elements stuck out weren’t compatible with the shrinkwrap system. Look carefully and you’ll see that crowd-scene cars don’t have wing mirrors for that reason.
Brain springs returned to control car suspension, and there was lots of work put into managing traffic.
Kanyuk can’t talk about crowd animation in Brave just yet, but shows an impressive trailer with a crowd at an archery contest. “You can probably guess what we used,” he smiles.
on Wednesday, May 9th, 2012 at 12:20 pm under Events.
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Tags: FMX 2012