Robust skin simulation in Incredibles 2

Robustly simulating the dynamics of skin sliding over a character's body is an ongoing challenge. Skin can become non-physically "snagged" in curved or creased regions, such as armpits, and create unusable results. These problems usually arise when it becomes ambiguous which kinematic surface the skin should be sliding along. We have found that many of these problems can be addressed by performing 2D ray-tracing over the surface of the mesh. The approach is fast and robust, and has been used successfully in Incredibles 2.