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Better Collisions and Faster Cloth for Pixar's Coco
Improves Pixar's Fizt cloth solver with enhanced collision handling and performance gains, addressing the high cloth demand of Coco's skeleton cast.
Abstract
Among the many technical challenges of Pixar's Coco was the need to handle cloth simulation for a densely populated city of skeleton characters. Skeletons posed new challenges to the collision algorithms of our in-house cloth system, Fizt. Continuous collision detection and response is an obvious solution to handling fast motion of thin geometry, but it presents us with a serious problem. In our production pipeline, geometry often starts in intersection. Animation also frequently causes kinematic surfaces to pinch the cloth between them and drive the cloth through itself. We present a solution for robustly allowing intersection recovery while employing standard continuous detection techniques. Coco also demanded more cloth than any previous Pixar film. To keep up with demand, Fizt needed to run much faster. We share our techniques for gaining performance in linear system assembly and solution, which should be applicable to most implicit solvers.
How to read this
- Category
- Production talk: cloth collision and solver performance
- Contributions
- Presents a method to robustly recover from initial intersections while still using standard continuous collision detection in Pixar's Fizt cloth system
- Handles cases where animation pinches cloth between kinematic surfaces or drives cloth through itself
- Shares performance gains in implicit-solver linear system assembly and solution to meet Coco's high cloth demand
- Context
- Improves on robust skinned-cloth collision and friction handling (Bridson et al., Robust Treatment of Collisions, Contact and Friction for a Skinned Cloth Simulation) within Pixar's in-house Fizt solver.Builds on: Robust Treatment of Collisions, Contact and Friction for a Skinned Cloth Simulation
- Correctness
- Studio practice, not peer-reviewed; results are production-proven on Coco's dense skeleton cast, and the intersection-recovery and speedup techniques are framed as broadly applicable but reported in a production context.
- Clarity
- Accessible talk; a single read conveys the problems and solutions, with the solver-assembly speedups stated at a practitioner level.
- How to read it
- Focus on the intersection-recovery strategy under continuous detection and the linear-solve speedups; useful as a reference if you maintain an implicit cloth solver, otherwise one pass suffices.
Built upon by
Nothing yet.
Related work
- A Safe and Fast Repulsion Method for GPU-based Cloth Self Collisions 2020 / TOG
- Robust Treatment of Collisions, Contact and Friction for a Skinned Cloth Simulation 2002 / SIGGRAPH
- Efficient and Stable Approach to Elasticity and Collisions for Hair Animation 2015 / DigiPro
- Untangling Cloth 2003 / SIGGRAPH
Keywords
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