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Position-Based Skinning for Soft Articulated Characters

Nadine Abu Rumman, Marco Fratarcangeli

CGFAcademic49 citesSkinning

Two-layer skinning that applies position-based dynamics constraints on top of LBS to achieve volume preservation and soft jiggle in real time.

Abstract

In this paper, we introduce a two‐layered approach addressing the problem of creating believable mesh‐based skin deformation. For each frame, the skin is first deformed with a classic linear blend skinning approach, which usually leads to unsightly artefacts such as the well‐known candy‐wrapper effect and volume loss. Then we enforce some geometric constraints which displace the positions of the vertices to mimic the behaviour of the skin and achieve effects like volume preservation and jiggling. We allow the artist to control the amount of jiggling and the area of the skin affected by it. The geometric constraints are solved using a position‐based dynamics (PBDs) schema. We employ a graph colouring algorithm for parallelizing the computation of the constraints. Being based on PBDs guarantees efficiency and real‐time performances while enduring robustness and unconditional stability. We demonstrate the visual quality and the performance of our approach with a variety of skeleton‐driven soft body characters.

How to read this

Category
Method: a skinning algorithm (two-layer LBS + PBD)
Contributions
  • Two-layered skin deformation that first applies linear blend skinning, then corrects it with geometric constraints solved via position-based dynamics.
  • Achieves volume preservation and jiggling while reducing classic LBS artefacts such as the candy-wrapper effect and volume loss.
  • Parallelizes constraint solving with a graph-colouring algorithm and gives the artist control over jiggle amount and affected skin region, in real time.
Context
Builds skeleton-driven soft-body skinning on top of Mueller et al.'s Position Based Dynamics, layering PBD constraints over standard linear blend skinning.Builds on: Position Based Dynamics
Correctness
Demonstrated on a variety of skeleton-driven soft-body characters with real-time, unconditionally stable PBD; results are geometric/plausible rather than physically rigorous, so it targets believable jiggle and volume, not accurate soft-tissue mechanics.
Clarity
Accessible if you know LBS and PBD; a first pass conveys the two-layer idea, a second pass for the constraint formulation and graph-colouring parallelism.
How to read it
First pass for the layering concept and artist controls; second pass on the PBD constraints and parallel solver if integrating into a real-time rig.

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