A Complete Treatment of D1 Discontinuities in a Discontinuity Mesh

This paper presents a treatment of first--order discontinuities (D1) that arise in discontinuitymeshes. An algorithm is described that, given a planar D1 discontinuity surface in a polyhedral scene, computes the corresponding discontinuity curves on the faces of the scene. A method is described to efficiently update the backprojection across a D1 discontinuity curve. An alternative update method is presented which is novel and numerically robust. Keywords: D1 discontinuity, discontinuity meshing, shadows, radiosity, global illumination. 1 Introduction For global illumination algorithms operating on polyhedral scenes illuminatedby an area light source, the discontinuity mesh is used to model accurately sharp changes in illumination [Hec91, Hec92a, LTG92, LTG93, Tam93]. The backprojection is a topological description of the boundary of the visible light source, as seen from some viewpoint. The discontinuity mesh is a set of maximal cells on the faces of the scene such that the backpro..