Adaptive Tessellation of Subdivision Surfaces in OpenSG

Abstract

The need for realistic models especially in virtual reality environments leads us to freeform shapes like subdivision surfaces. Based on a standard polygonal mesh, the modeller can build various kinds of shapes using an arbitrary topology and special geometrical features like creases. Nowadays, it also is a part of most standard modelling packages like Maya and 3DStudio Max. However, the interactive display of subdivision surfaces in current scenegraph systems as static level-of-details is unpractical, because of the exponentially increasing number of polygons during the subdivision steps. Therefore an adaptive algorithm, choosing only the necessary quads and triangles, is required to obtain good looking images at high framerates. In this paper we present a rendering algorithm considering the static surface properties like curvature as well as viewdependent properties like silhouette location and projection size. Without modifying the basis mesh, the method works patchwise and tesselates each patch recursively using a new datastructure, called Slate. We show that the algorithm can be implemented efficiently using direct OpenGL. In comparison we consider the algorithm’'s integration into the scenegraph system OpenSG, where the scenegraph node feeds into an indexed-face-set node.