Distributed Ray Tracing - Summary - 782 Lab3 - Distributed Raytracer

Vince Scheib
Roger Crawfis
CIS 782
Summery of Paper
February 25, 1999

Summarization of:
Cook, Robert L. Thomas Porter, Loren Carpenter. "Distributed Ray Tracing". Proceedings of SIGGRAPH'84. In Computer Graphics 18, 3, pp. 137-145, July 1984.

Ray tracing, the process of recursively intersecting a parameterized line equation with surfaces, is a simple and elegant rendering algorithm. Shadows, reflection, and refraction are easily attained, while much more difficult with alternative display techniques. Extending this algorithm to distributed ray tracing incorporates: blurred reflections, blurred refraction, soft shadows, depth of field, and motion blur. This increases the quality of rendered images dramatically, with relatively little cost.

The modification to the traditional ray tracer is very simple. Sample each pixel multiple times and each time distribute scene parameters. This point samples many parameters that have a large range of values. Finally, average the samples together for an approximation of the contribution of each parameters' diverse range. Each of the effects are addressed individually below.

Blurred Reflections
Reflections in the traditional ray tracer are perfect, or mirror like. In the distributed algorithm the reflected ray is perturbed slightly. This creates a glossy reflection, where objects in the reflection are increasingly blurry the farther away they are.

Blurred Refraction
In the same way that the reflected ray is perturbed, so is the refracted ray. This parallels the glossy reflection with glossy transparency.

Soft Shadows
Sampling a light source over an area expands upon the simple 'point light' of most ray tracers. When checking for shadows, a random point is selected from a light source with probability equal to the proportional amount of light emanating from that point. This simulates an area light source, which causes soft shadows.

Depth of Field
Distributing the eye position over the area of a virtual lens, while maintaining the center of interest, causes defocusing of objects not on the focal plane.

Motion Blur
Randomly positioning objects according to their time parameterized description of position in space causes motion blur. These sample points should be taken from the current frame to be rendered plus or minus some epsilon.

As stated above, each of these parameters is distributed per pixel sample. Averaging together multiple samples simultaneously averages together the point samples of each parameter. Thus all effects can be obtained for approximately the same cost.