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Procedural wrinkles generation in the implicit skinning framework
Abstract
Among the procedural skinning methods, implicit skinning [Vaillant et al. 2014] allows to achieve effects like bulge in contact with the use of gradient-based operators, but fine details like wrinkling are missing. Physics-inspired methods make use of the stretch tensor to produce controllable, believable results at acceptable computational cost [Rohmer et al. 2010]. We propose a method that generates plausible and temporally-coherent wrinkles for skeleton-driven 3D animated characters, by extending the implicit skinning framework.
We present a novel approach for interactive character skinning,
which is robust when character movements are extreme, such as
those involving contact between different parts of the skin and sharp
bending angles at joints. Our approach builds on the basic idea of
implicit skinning, namely approximate the character at each animation
step by a 3D scalar field in which mesh-vertices are appropriately
re-projected. Instead of being bound by an initial skinning
solution, used to initialize the shape at each time step, we use
the skin mesh to directly track iso-surfaces of the field over time.
Technical problems are two-fold: firstly, all contact surfaces generated
between skin parts should be captured as iso-surfaces of the
implicit field; secondly, the tracking method should capture elastic
skin effects when the joints bend, but also insure that the skin
comes back to its rest shape when the character comes back to
rest. Our solutions to these problems include: new composition
operators enabling the combination of blending effects with local
self-contact between implicit surfaces, and a tangential relaxation
scheme derived from the as-rigid-as possible energy to solve the
tracking problem. The result is a robust interactive system that
can handle contacts in a way that is visually plausible, exhibits the
global effect of skin elasticity (sliding), and is suitable for use in a
production pipeline.
Moving garments and other cloth objects exhibit dynamic, complex wrinkles. Generating such wrinkles in a virtual environment currently requires either a time-consuming manual design process, or a computationally expensive simulation, often combined with accurate parameter-tuning requiring specialized animator skills. Our work presents an alternative approach for wrinkle generation which combines coarse cloth animation with a post-processing step for efficient generation of realistic-looking fine dynamic wrinkles. Our method uses the stretch tensor of the coarse animation output as a guide for wrinkle placement. To ensure temporal coherence, the placement mechanism uses a space-time approach allowing not only for smooth wrinkle appearance and disappearance, but also for wrinkle motion, splitting, and merging over time. Our method generates believable wrinkle geometry using specialized curve-based implicit deformers. The method is fully automatic and has a single user control parameter that enables the user to mimic different fabrics.
Moving garments and other cloth objects exhibit dynamic, complex wrinkles. Generating such wrinkles in a virtual environment currently requires either a time-consuming manual design process, or a computationally expensive simulation, often combined with accurate parameter-tuning requiring specialized animator skills. Our work presents an alternative approach for wrinkle generation which combines coarse cloth animation with a post-processing step for efficient generation of realistic-looking fine dynamic wrinkles. Our method uses the stretch tensor of the coarse animation output as a guide for wrinkle placement. To ensure temporal coherence, the placement mechanism uses a space-time approach allowing not only for smooth wrinkle appearance and disappearance, but also for wrinkle motion, splitting, and merging over time. Our method generates believable wrinkle geometry using specialized curve-based implicit deformers. The method is fully automatic and has a single user control parameter that enables the user to mimic different fabrics.