From Procedural Panda-monium to Fast Vectorized Execution using PCF Crowd Primitives

Aaron Lo, Venkateswaran Krishna, J.D. Northrup, Mark Hessler, Arnold Moon, Michael Lorenzen, Jonah Laird, and Paul Kanyuk


In animation and VFX, crowds are too often considered an "edge case", to be handled by specialized pipeline outside the main workflows. Requirements of scale and traditional reliance on history based simulation have been obstacles to properly building crowd systems into the core functionality of digital content creation software. Pixar's crowds team has worked to reverse this trend, developing a fast vectorized crowd system directly within the execution engine of our proprietary animation software, Presto. Dubbed Pcf, for Presto Crowds Framework, this system uses aggregate models, called crowd primitives, to provide artists directly manipulable crowds while maintaining proceduralism for mass edits. Like traditional models, they contain rigs (a graph of operators) which run parallelized through Presto's execution engine [Watt et al. 2014], but rather than posing points, they set joint angles and blendshape weights to pose entire crowds. The core operations of crowd artists: placement, casting, clip sequencing, transitions, look-ats, and curve following, are all well expressed as rigging operators (known as "actions" in Presto parlance) in Pcf. They provide interactive control of entire crowds in context using the same animation tool as our layout artists, animators, simulation TDs, etc. The first film to use Pcf, Turning Red, reaped massive benefits by building a stadium's worth of characters in a fraction of the time of previous films' efforts. However, because Pcf is tightly integrated into Presto, the benefits extended beyond efficiency for the crowds team. By providing our layout department Pcf rigging controls, they were able to shoot inside the crowd and use procedural operators to clear room for the camera and maintain crowd density only where needed. Similarly, the principal animation team could animate main characters in context of the crowd they were acting in, providing the proper context which all too often is absent in crowd shots. Taken together Pcf, is a huge step forward in bringing crowds out of the margins and into the core of animation workflows at Pixar, demonstrating that fast vectorized crowds can be an integral part of digital content creation software.

Paper (PDF)

Siggraph Talk 2022