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[Duane D. Frank]

Okay ye all Iris graphics gods, I have another question.
I am trying to use depth cueing and it works well and exactly as I
would expect and well when I use an Orthographic (parallel) 
projection.  However, when I try and do the same thing using
a Perspective project (with or without lookat call or with or without
translations in the z-direction) I have to play with it a lot to
get it to come out right, and there seems to be no rhyme or reason
to how it behaves.  The values I come up with are usually not even
near what I expect, and small changes in the values that I pass to
shaderange or setdepth sometimes make drastic changes in the picture
and other times doesn't change it at all. 
Does anyone have any hints, suggestions, theories, equations or 
anything that might shed some light on the use of depth cueing while
using a perspective projection?
Thanks in advance,
Duane D. Frank, (dfrank at cs2.cs.wsu.edu) or (22414843.WSUVM1.BITNET)