Textured Silhouette Edges and Pencil Rendering on the Geometry Shader

We are Pedro Hermosilla and Pere-Pau Vázquez of the MOVING graphics group at UPC in Barcelona. Our contribution to GPU Pro deals with Non-Photorrealistic Rendering on the GPU.

Silhouette detection is a key issue in many non-photorealistic rendering algorithms. Silhouettes play an important role in shape recognition because they provide one of the main cues for figure-to-ground distinction. However, since silhouettes are view-dependent, they must be computed per frame. In this paper we present a couple of techniques that make use of the Geometry Shader in order to generate and texture silhouettes and to simulate pencil rendering in realtime. We provide both the insights of the technique and the source code of a sample application that makes use of the techniques to render a simple object.