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Regularized Kelvinlets: Sculpting Brushes Based on Fundamental Solutions of Elasticity

Fernando de Goes, Doug L. James

SIGGRAPHPixar27 cites2 descendantsRiggingSkinning

Closed-form elastic sculpting brushes for volume-preserving grab, scale, twist, and pinch used in character pose-space sculpting workflows.

Abstract

We introduce a new technique for real-time physically based volume sculpting of virtual elastic materials. Our formulation is based on the elastic response to localized force distributions associated with common modeling primitives such as grab, scale, twist, and pinch. The resulting brush-like displacements correspond to the regularization of fundamental solutions of linear elasticity in infinite 2D and 3D media. These deformations thus provide the realism and plausibility of volumetric elasticity, and the interactivity of closed-form analytical solutions. To finely control our elastic deformations, we also construct compound brushes with arbitrarily fast spatial decay. Furthermore, pointwise constraints can be imposed on the displacement field and its derivatives via a single linear solve. We demonstrate the versatility and efficiency of our method with multiple examples of volume sculpting and image editing.

How to read this

Category
Method: closed-form elastic deformation primitives (sculpting brushes)
Contributions
  • Brush-like grab, scale, twist, and pinch displacements derived as regularized fundamental solutions of linear elasticity in 2D and 3D
  • Compound brushes with arbitrarily fast spatial decay for fine local control
  • Pointwise constraints on the displacement field and its derivatives via a single linear solve
Context
Grounds interactive sculpting in classical linear elasticity (Kelvin's fundamental solutions), offering an analytical alternative to mesh-based or FEM volume deformation for pose-space sculpting workflows.
Correctness
Built on linear elasticity in infinite media, so results are physically plausible rather than exact for finite or nonlinear materials; the closed-form, regularized formulation buys real-time interactivity but the demonstrations are sculpting and image-editing examples rather than a quantitative validation.
Clarity
Conceptually accessible (brush metaphor); a first pass conveys the idea, a second pass is needed for the elasticity formulation and regularization.
How to read it
First pass for the brush vocabulary and the regularization idea; do a careful second pass on the fundamental-solution math and the constraint solve if you intend to implement or extend the brushes.

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