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From: iris@granny.engin.umich.edu (Yuval Roth Tabak )
Newsgroups: comp.sys.sgi
Subject: problems with depthcue ?
Message-ID: <IRIS.91Feb19131752@granny.engin.umich.edu>
Date: 19 Feb 91 18:17:52 GMT
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Reply-To: iris@caen.engin.umich.edu
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I am developping an application using multiple windows.
In one of the windows I am using depthcuing (depthcue, RGBmode,
lRGBrange) to display the z-buffer, and I have encountered 
some disturbing inconsistencies with the description
in the standard documentation:
1. The color range does not seem to be linear with respect
   to distances from the viewing position (it seems to be stretched
   much more closer to the viewer than further away).
   I did use lsetdepth before lRGBrange to set the smae MIN and MAX
   values.
   -- I was able to get around the problem by playing with the range
   in lRGBrange so that the colors change in the depth region that I
   am mostly interested in. However, this does not explain the inconsistency.
2. When the scene is drawn with depthcue, there seems to be a peculiar
   orientation preference.
   More precisely, when I rotate the scene around the viewing axis
   (by using lookat() and changing the twist angle) the colors in
   the window change drastically, also the color `gradient' seems to
   be going horizontally in the image regardless of orientation of 
   planes in the scene. If the colors represent z-values
   (distances from viewing point of planes perpendicular to the viewing axis),
   then the colors should not change this way (should they ?!).
   Another perplexing effect is that planes that intersect each other
   in the scene have different colors (in the depthcue window) at the 
   intersection line -- this is more puzzling since a similar window 
   displaying the same scene regularily displays the scene correctly, i.e. 
   the z-buffer itself is working properly.

If any body has encountered similar problems, and/or if someone can clear
some of my ignorance, I would appreciate it.

Yuval
--
=============================================================================
Yuval Roth                    |    Internet: iris@caen,engin.umich.edu
University of Michigan AI Lab |    1101 Beal Ave., Ann Arbor, MI 48109-2110
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