Real-time ambient occlusion for dynamic character skins

Abstract

We present a single-pass hardware accelerated method to reconstruct compressed ambient occlusion values in real-time on dynamic character skins. This method is designed to work with meshes that are deforming based on a low-dimensional set of parameters, as in character animation. The inputs to our method are rendered ambient occlusion values at the vertices of a mesh deformed into various poses, along with the corresponding degrees of freedom of those poses. The algorithm uses k-means clustering to group the degrees of freedom into a small number of pose clusters. Because the pose variation in a cluster is small, our method can define a low-dimensional pose representation using principal component analysis. Within each cluster, we approximate ambient occlusion as a linear function in the reduced-dimensional representation. When drawing the character, our method uses moving least squares to blend the reconstructed ambient occlusion values from a small number of pose clusters. This technique offers significant memory savings over storing uncompressed values, and can generate plausible ambient occlusion values for poses not seen in training. Because we are using linear functions our output is smooth, fast to evaluate, and easy to implement in a vertex or fragment shader.