Immediate-mode Ray-casting Immediate-mode Ray-casting

We propose a simple modi cation to the classical polygon rasterization pipeline that enables exact, e cient raycasting of bounded implicit surfaces without the use of a global spatial data structure or bounding hierarchy. Our algorithm requires two descriptions for each object: a (possibly non-convex) polyhedral bounding volume, and an implicit equation (including, optionally, a number of clipping planes). Unlike conventional raycasters, the modi ed pipeline is unidirectional and operates in immediate mode, making hardware implementation feasible. We discuss an extension to the OpenGL state machine that enables immediate-mode raycasting while making no modi cation to OpenGL's architecture for high-performance polygon rendering. A software simulation of our algorithm generates scenes of visual delity equal to those produced by a conventional raycaster, and superior to those produced by a polygon rasterizer, signi cantly faster than either existing method alone.