Skeletal Animation with Anisotropic Materials

In this chapter, we present an integrated real-time system for animation of skeletal characters with anisotropic tissues. Existing geometrically-based skinning techniques suffer from obvious volume distortion artifact, and they cannot produce secondary dynamic motions, such as jiggling effects. Physically-based skinning with FEM models has high computational cost that restricts its practical applications. To solve these problems, we introduce a strain-based Position Based Deformation (PBD) framework for skeletal animation. It bridges the gap between geometric models and physically-based models, and achieves both efficient and physically-plausible performance. Natural secondary motion of soft tissues is produced. Anisotropic deformations are made possible with separately defined stretch and shear properties of the material, using the user-designed frame-field. Owing to the efficiency and stability of our proposed layered constraint solving scheme, we can achieve real-time performance, and the system is robust with large deformations and degenerate cases.