In production environments, facial rigging is commonly done by either geometric deformations or blendshapes. Geometric deformations are driven by simulated muscle actions, which are loosely based upon the dynamics of facial tissue [Magnenat-Thalmann et al. 1988]. Blendshapes interpolate a large number of sculpted shapes [Bergeron and Lachapelle 1985]. The former approach is intuitive, yet slow and less precise. The latter is fast, yet memory intensive and sensitive to model changes. Conventional implementations of both approaches are difficult to generalize in order to build rigs quickly and retarget animation efficiently.

DrivenShape is a data-driven deformation that uses pre-computed data (a.k.a. targets) to approximate the effects of a computationally expensive cloth simulation [Kim and Vendrovsky 2008]. Rather than computing a true, accurate solution, DrivenShape produces a quick approximation that satisfies an acceptable margin of error, where error is defined as a difference in appearance or shape.

Radial basis functions (RBFs) are important in computer graphics, with widespread use in reconstruction, animation, etc. In pose space deformation (PSD) [Lewis et al. 2000], RBFs are used to perform shape interpolation for pose-driven deformations. The behavior of an RBF depends on its particular definition. For artists, the relationship between definition and behavior is not intuitive. We suggest a method for artists to better understand RBF behavior through visualization and to evaluate RBF functions according to the requirements of a production environment.

Pose Space Deformation (PSD) [Lewis et al. 2000] is a shape interpolation technique for animation. This method uses radial basis functions (RBFs) to perform per-vertex, multidimensional scattered-data interpolation. This formulation effectively interpolates a driven shape according to a set of targets, each at a particular driver value. In the case of correcting a pinched elbow, the skinned geometry is the driven, the targets are the sculpted adjustments, and the driver is the elbow joint. This paper presents some practical experience with PSD acquired while creating the film BOLT.

The paper identifies reusable interactions and presents them as an important construct for the development and reuse of software for computer animation. A reusable interaction manages the flow of information among software components. They are first class entities that are easy to adapt, to organize hierarchically, and to operate dynamically. In computer animation and other time dependent systems, communications among components evolves as (simulated) time advances. With reusable interactions, developers carefully identify and control this evolution. A novel approach for computer animation that employs reusable interactions is presented in the form of the RASP toolkit. The toolkit provides tools to manage and to organize hierarchically interactions over time. The hierarchical organization of the tools promote multiple levels of reuse. Each level introduces greater means to coordinate the interactions and to reuse them appropriately.