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Stretchable and Twistable Bones for Skeletal Shape Deformation
Extends LBS bones to support stretch and twist DOF, eliminating candy-wrapper artifacts without extra helper joints.
Abstract
Skeleton-based linear blend skinning (LBS) remains the most popular method for real-time character deformation and animation. The key to its success is its simple implementation and fast execution. However, in addition to the well-studied elbow-collapse and candy-wrapper artifacts, the space of deformations possible with LBS is inherently limited. In particular, blending with only a scalar weight function per bone prohibits properly handling stretching, where bones change length, and twisting, where the shape rotates along the length of the bone. We present a simple modification of the LBS formulation that enables stretching and twisting without changing the existing skeleton rig or bone weights. Our method needs only an extra scalar weight function per bone, which can be painted manually or computed automatically. The resulting formulation significantly enriches the space of possible deformations while only increasing storage and computation costs by constant factors.
How to read this
- Category
- Method: an extension to linear blend skinning (stretch and twist)
- Contributions
- A simple modification of the LBS formulation that enables stretching (bones changing length) and twisting (shape rotating along the bone) without changing the existing skeleton rig or bone weights
- Requires only one extra scalar weight function per bone, paintable manually or computed automatically
- Significantly enriches the LBS deformation space while increasing storage and computation by only constant factors
- Context
- Builds directly on linear blend skinning and the authors' Bounded Biharmonic Weights (Jacobson and Sorkine 2011) for the weight functions, addressing LBS limits beyond the classic elbow-collapse and candy-wrapper artifacts.Builds on: Bounded Biharmonic Weights for Real-Time Deformation
- Correctness
- The appeal is real-time efficiency and rig compatibility; as an LBS variant it inherits LBS's geometric (non-physical) nature, and the added expressiveness depends on a sensible extra weight function, so it enriches rather than fully resolves all blend-skinning artifacts.
- Clarity
- Notably accessible; a first pass conveys the idea and its practicality, and a short second pass suffices for the (compact) formulation.
- How to read it
- First pass gives the core trick and why it is cheap and rig-preserving; a brief second pass on the formula and the extra weight function is enough to apply it.
Builds on
Built upon by
Related work
- Elasticity-Inspired Deformers for Character Articulation 2012 / SIGGRAPH Asia
- Skinning: Real-time Shape Deformation 2014 / SIGGRAPH
- Geodesic Voxel Binding for Production Character Meshes 2013 / SCA
- Automatic Rigging and Animation of 3D Characters 2007 / SIGGRAPH
Keywords
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