Rendering optimisations for stylised sketching

Abstract

We present work that specifically pertains to the rendering stage of stylised, non-photorealistic sketching. While a substantial body of work has been published on geometric optimisations, surface topologies, space-algorithms and natural media simulation, rendering-specific issues are rarely discussed in-depth even though they are often acknowledged. We investigate the most common stylised sketching approaches and identify possible rendering optimisations. In particular, we define uncertainty-functions, which are used to describe a human-error component, discuss how these pertain to geometric perturbation and textured silhouette sketching and explain how they can be cached to improve performance. Temporal coherence, which poses a problem for textured silhouette sketching, is addressed by means of an easily computed visibility-function. Lastly, we produce an effective yet surprisingly simple solution to seamless hatching, which commonly presents a large computational overhead, by using 3-D textures in a novel fashion. All our optimisations are cost-effective, easy to implement and work in conjunction with most existing algorithms.