Distributed Ray-Tracing

Summary

Distributed ray-tracing is a term that is commonly misconstrued, and often associated with the concept of parallel computing, where the calculations required to render an image are distributed across a network of processing nodes. The more appropriate term, ‘parallel ray-tracing’ is typically used to resolve the ambiguity.Whitted Ray-TracingIn the traditional Whitted algorithm, a ray is spawned, for every pixel in the screen. That ray is tested against the geometry of the scene to check whether an intersection point exists. If an intersection is found, depending on the properties of the surface, a limited number of additional purpose specific rays may be generated.These rays can either be shadowing rays, that check whether the resolved point is visible or not by the light sources in the scene, or reflection / transmission rays that recursively trace a specular light path to model reflection or transmission events in perfect mirrors and transparent media.While the algorithm can produce aesthetically pleasing results and is able to model interactions that traditional rasterization fails to represent at the same level of visual fidelity, it can only simulate a limited set of interactions and light paths, most of which are not typically observed in the real world. In a mathematical sense, it’s intuitive to think of the limitations in terms of the rendering equation which requires the evaluation of several integrals. Conventional ray-tracing is estimating illumination using a single sample across the entire domain, which constitutes a particularly crude approximation.In summary some of the limitations are:Shadows have a hard edge, as only infinitesimally small point light sources of zero volume can be simulated, with binary shadow queries that use a single ray.Reflection / Refraction can only simulate a limited set of light paths, for perfect mirror surfaces, or perfectly homogeneous transparent media.More complex effects like depth of field are not supported.Distributed...