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From: npw@eleazar.dartmouth.edu (Nicholas Wilt)
Newsgroups: comp.graphics
Subject: Ray Tracing Optimization Idea
Keywords: Exploit coherence
Message-ID: <1991Mar21.183340.19319@dartvax.dartmouth.edu>
Date: 21 Mar 91 18:33:40 GMT
Sender: news@dartvax.dartmouth.edu (The News Manager)
Organization: Dartmouth College, Hanover, NH
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Originator: npw@eleazar.dartmouth.edu

I had a simple, interesting idea to make tracing primary rays more
efficient.  Cache the last object intersected; intersect with it
first and if hit, determine whether it is still the nearest object as
follows:
	1. Fire a ray from the intersection back at the eye
	2. If no object is intersected, the cached object is still nearest
	3. If any objects are intersected, find the farthest intersection
	   that's not beyond the eye.  This is the new nearest intersection
	   to the eye.

Since many objects such as polygons and bounding volumes (with K-K
traversal) respond well to rays which are heading away from them, it seems
to me that this scheme could work well for certain scenes.

Has anyone read about an approach which takes advantage of coherence in
this way?  Has anyone implemented the approach?  I welcome any comments.

--Nick
  npw@eleazar.dartmouth.edu