TEXTURE MAPPING THE BLOBTREE Mark Tigges Brian Wyvill Dept. of Computing Science University of Calgary, Calgary, Alberta, Canada mtigges@cpsc.ucalgary.ca blob@cpsc.ucalgary.ca ABSTRACT Recently an automatic solution to the problem of applying 2D textures to an implicit surface has been introduced [13]. The method derives a uv-texture coordinate system by tracing particles from the implicit surface to a support surface. In this paper we describe the adaptation of this algorithm to the BlobTree data structure. The BlobTreeprovides an implicit modelling system through a hierarchy of blends, CSG and warping applied to primitives. There are several problems involved in applying textures in such a general modeling system, particularly across CSG junctions. In this paper we identify these problems and introduce some possible solutions. 1. INTRODUCTION Implicit surfaces, those defined by an iso-contour of an implicit function [3], have enjoyed an active research community for over a decade. The use of this class of surfaces outside of academia has been restricted to only special case examples, partly due to the lack of both good interactive modeling systems and the inability to apply 2D textures. The use of implicit surfaces in creation of cartoon like characters [8] has been outlined and extension of implicit surface modeling to include CSG operations have made description of solid models for engineering possible [11]. These steps are progress towards fulfilling the needs for commercial use. One open problem which has only partially been resolved, is the derivation of a 2D texture coordinate system directly from the definition of the skeletal implicit model. Parametric modeling techniques have the advantage over implicit surface techniques, that a natural 2D texture coordinate system can be easily derived from parametric space. Implicit surfaces do not yield a two dimensional parameterization easily. A computed parameterization would need to be suitable for use in application of texture maps, and for use in displacement mapping [2]. Solid texturing techniques have been applied to implicit surfaces [12], but these methods do not allow an animator to apply a bi-dimensional texture onto an implicit surface. For example, the application of a textured face to an animated figure. Ability to generate two dimensional mappings for the surface of an implicit model is required for iso-surface techniques to enter into mainstream modeling and animation use in computer graphics. 1.1. The BlobTree The BlobTree [9] provides a hierarchical data structure for the definition of complex models built from implicit surfaces, CSG Boolean operations and field warping functions. Models built with this system are generally considered as the hierarchical composition of multiple objects rather than a complete object (see figure 1). Typically these components are defined with differing surface attributes: specularity, reflectance, transmittance etc; accordingly we wish to include 2D surface parameterizations for application of texture maps. In this work we present extensions to the BlobTree that allow the definition of such parameterizations and their use for texture mapping. 1.2. 2D Texturing of Implicit Surfaces An algorithm to map a point on an iso-surface to a point in a defined texture space was introduced by Zonenschein et al. [13]. The method bounds the iso-surface to another surface (known as the support surface) which