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Pseudo-Collisions: A Method for Preventing Fur-Skin Intersections Without Physical Simulation
Marco Romeo, Carlos Monteagudo Manas, Hristo Arabadzhiyski, Lucas Ferry, Julia Visser Conesa, Matthew Traynar
Lightweight pseudo-collision method preventing fur-skin intersection without full simulation, enabling scalable creature grooming at production scale.
Abstract
We introduce Pseudo-Collisions (PC), a numerical and time independent method to reduce the collisions between short fur and the skin of an asset as it deforms during animation. Typically, solving these intersections in a standard workflow would require a lot of time to set up and simulate each strand or their guide curves. With our solution, this can be achieved with a light post-process on top of the applied fur. This is achieved by adjusting the transformation matrix used to place the strands on the animated skin so that its rotation component smoothly lifts the hair where necessary. The algorithm dynamically adjusts the orientation of the animated strands to reduce the intersections using different pieces of information including the direction of the strands, the placement matrices for each strand on the rest and the animated skin meshes, as well as the change in the surface’s curvature due to the deformation. Pseudo-Collisions was successfully used during the production of Mufasa: The Lion King [Disney© 2024] and the set of parameters made available to the users to modulate the results of the correction is also presented.
How to read this
- Category
- Method: a fur-skin intersection-reduction technique (production)
- Contributions
- Pseudo-Collisions, a numerical, time-independent method that reduces short-fur penetration of deforming skin without per-strand or guide-curve simulation
- A correction that adjusts each strand's placement-matrix rotation using strand direction, rest and animated placement matrices, and surface curvature change
- An exposed, user-tunable parameter set, validated on the production of Mufasa: The Lion King
- Context
- Sits alongside production fur-motion systems such as DreamWorks' Skunk, offering a lightweight post-process alternative to simulating fur strands or guides.Builds on: Skunk: DreamWorks Fur Motion System
- Correctness
- Because it is a time-independent geometric correction rather than a physical simulation, it targets short fur and reduces (not provably eliminates) intersections; behavior on long fur or large deformations, and temporal coherence, are the things to watch.
- Clarity
- Practitioner-oriented and accessible; a first pass conveys the trick, a second pass clarifies the matrix-adjustment math.
- How to read it
- Read for the placement-matrix rotation idea and the parameter knobs; one careful pass on the correction formula suffices unless you intend to reimplement it.
Builds on
Built upon by
Nothing yet.
Related work
- Creatures in Houdini | Ahmed Gharraph | FMX 2019 2019 / FMX
- Framestore Creatures & Houdini | Framestore | Character FX & Crowds Production Talks 2019 / Houdini
- Hair and Fur in an Evolving Pipeline 2020 / SIGGRAPH
- Cloth and Skin Deformation with a Triangle Mesh Based Convolutional Neural Network 2020 / CGF
Keywords
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