Robust Iso-Surface Tracking for Interactive Character Skinning

Abstract

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.