High Level Control of Implicit Surfaces for Character Animation

Implicit surfaces, also known as blobby molecules [2], metaballs [14] or soft objects [22], are particularly suitable for modelling smoothly blended, “plasticine” objects. One of their most attractive features is their deformability. The shape of an object can be altered by simply moving the skeletal elements. A closed, smoothly blended surface is always guaranteed although the topology of an object may change. In this paper we will look closer at the use of implicit surfaces for character animation. We use a layered model to represent characters. A graph defines an articulated figure. The limbs which cover the articulated figure are designed by a user and form the body of a character. The body is covered by flesh which can be automatically generated by the system (skin) or partially designed by a user (strands of flesh: hair, a tail etc.). We use a mixture of manual and automatic motion control. Keyframes for the articulated figure are specified using dance notation and the motion of flesh is automatically generated by the system. A user can control the motion of flesh at a high level using a set of adjustable parameters (gravity, flesh firmness and exaggeration). We illustrate our approach using a dancer performing to the given choreography.