Interactive character animation using dynamic elastic simulation
This dissertation describes a framework for interactively animating characters such as humans and animals based on dynamic elastic simulation. Using dynamic simulation, the secondary motion of the character's soft tissue is computed automatically, and the shape of the character reflects environmental influences not anticipated by the animator. To endow an elastic body with animation-friendly control mechanisms we unify dynamic elastic simulation, skeleton-driven deformation, and shape interpolation. We model a character as an elastic body simulated using the finite element method. For computational efficiency, we embed the object in a coarse subdivision volume. Subdivision provides topological flexibility, smooth deformations, and hierarchical structure for adaptive simulation. Skeletal control is made efficient by aligning the subdivision control lattice with the skeleton. In order to make the computation of elastic dynamics efficient enough for interactive applications, we introduce a new method of linearizing the nonlinear equations of elasticity dependent on the pose of the character. Our framework also provides a mechanism to control the shape of the character via abstract parameters. Because the shape of a character is determined by physical dynamics, it cannot simply be dictated as in traditional computer animation. Instead, we introduce forces to control the shape. Force-based shape control guides the shape of the character but is combined with other forces acting on the system and integrated into the dynamics. The result is a system that produces interactive animations with automatic secondary flesh dynamics, and at the same time gives the animator a large degree of control over the pose and shape of the character.