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The Fashionista Twins: Conjoined Hair in Trolls
Describes the grooming, rigging, and simulation pipeline for character-connected hair shared between conjoined twins in Trolls.
Abstract
This DigiPro talk presents the techniques used to create the seamlessly connected, looped hair for the conjoined Fashionista Twins, Satin and Chenille, in the film Trolls. The twins are treated as two instances of a single character asset, and grooming achieves a mirrored look by mirroring the deformable guide hairs and scalp about the vertical axis before relaxing them. A new render-time styler called MatchEnds, built into the in-house Willow hair geometry library, geometrically connects matched follicle curves across the two heads using equal pulling with falloff, Laplacian smoothing of shared CVs, and tangency matching. For motion, a modified Spline IK system drives joint chains spanning the combined hair length with cross-character constraints, and the shot pipeline outputs mirrored guides and render hairs in Satin's reference space to assemble the full renderable hair asset.
How to read this
- Category
- Production talk: a grooming, rigging, and simulation breakdown
- Contributions
- Demonstrates mirrored grooming by mirroring deformable guide hairs and scalp about the vertical axis before relaxing
- Shows a render-time MatchEnds styler that geometrically connects matched follicle curves across two heads via equal pulling with falloff, Laplacian smoothing, and tangency matching
- Presents a modified Spline IK system with cross-character constraints to drive the combined hair length, outputting mirrored guides in one twin's reference space
- Context
- Relates to film hair grooming and simulation pipelines, addressing the unusual requirement of seamlessly conjoined, looped hair shared between two characters treated as instances of a single asset.
- Correctness
- Studio practice, not peer-reviewed; production-proven for the Fashionista Twins but a bespoke solution to a specific conjoined-hair problem, so its techniques are special-purpose rather than broadly general.
- Clarity
- Accessible to hair and rigging practitioners; one read conveys the connection trick and the cross-character rig.
- How to read it
- Read once for the asset-sharing idea and the MatchEnds connection approach; revisit specific sections only if you face a similar shared or looped hair problem.
Related work
- Hair Emoting with Style Guides in Turning Red 2022 / SIGGRAPH
- Hair and Fur in an Evolving Pipeline 2020 / SIGGRAPH
- Patch-based Surface Relaxation 2018 / SIGGRAPH
- A Biologically-Parameterized Feather Model 2002 / Eurographics
Keywords
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