Reliable Soft Shadows over Implicit Surfaces

Abstract

This paper introduces an efficient and reliable algorithm to create soft shadows for ray traced implicit surfaces. In a classical soft shadow creation process, many rays have to be traced to calculate how much of the area light is visible from a point. In our approach, we trace from a point a beam that covers the area light. If the beam is not occluded, the point can be safely discarded because the use of Interval Arithmetic guarantees that the point is fully lit by the area light. In this case, extra rays are not traced, thus extra intersection tests are not required. Our soft shadow algorithm is then 38% to 59% faster than an algorithm based in a regular number of beams traced for each point. Besides, the using of beams based on Interval Arithmetic guarantees that thin details of the surfaces are not lost during the process.