Spherical Blend Skinning on GPU

Skeletal animation is commonly used for real-time animation of humans, animals, etc. There are several methods available for propagating a skeleton pose to a skin mesh, but unfortunately, one of the most commonly used methods, linear blend skinning, has inconvenient artifacts. It is, however, a simple and very fast method, and it can easily be implemented on a GPU. An improved skinning method, spherical blend skinning, has been proposed. This method requires a rotation center to be computed by solving a linear matrix system, and further, it requires interpolation of quaternions. Thus, this method is more complex and slower than linear blend skinning, but it requires and produces exactly the same input and output as linear blend skinning making it easy to interchange the two methods. In this paper, we propose a method that enables spherical blend skinning to run on a GPU with performance comparable to GPU implementations of linear blend skinning, making spherical blend skinning a possible choice for many real-time applications such as computer games. The proposed method is implemented in C++, OpenGL [Shreiner et al. 2005] and Cg [NVIDIA 2005] in the OpenTissue framework [OpenTissue 2007]. Shaders are shown in pseudo code general enough to make implementation in other language combinations quite easy.