Traitement temps-réel des déformations de la peau et des tissus sous-cutanés pour l'animation de personnages

Traditional animation of characters relies on the design of an external shape, called the skin,and an internal skeleton, composed of a hierarchy of frames, which enables one to control thedeformation of the skin in a consistent and predictable way. Since it is relatively efficient, thisskinning technique is widely used in computer graphics production environments. However, italso has inherent limitations. Even if a large amount of research work were to solve the otherknown deficiencies of the technique, the fundamental issue remains that some types of deforma-tions can never be generated by it. Examples of this are the dynamic wrinkles of skin or clothesnear joints, or inertia effects of muscles and fatty tissues when sharp movements are involved.In this thesis, we propose two modeling and animation techniques which address those specificproblems, and which can be used to enhance existing animation sequences.Our first contribution addresses the addition of dynamic effects which are typical for themuscles/fatty tissues layer to kinematic deformations obtained through skinning or an equivalenttechnique. The dynamic effects are computed using a simplification of linear elasticity theory.To this end, dynamic elements which associate damped spring vibrations with a set of per ver-tex weights for the mesh, perform a so called dynamic skinning. The location, frequency andamplitude of the effects can be specified in a straightforward way by the user.On top of this layer comes a thin surface which can either represent the skin or clothes. Thissurface of almost constant area follows muscle and fatty tissue deformations by wrinkling whenit gets compressed. In order to guide this behavior the user interactively positions and orientsa deformable control curve of constant length on a mesh, and specifies its region of influence.During the animation geometric folds are generated in real-time in the regions covered by thetool, and the mesh is locally refined on the fly where and when needed.