z-buffer values in ortho pr

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Shawn Soeder (shawn_soeder++at++esplt14m-s.grumman.com)
14 Oct 1996 17:18:09 -0400

Performers,

I am reading the z-buffer values in ortho projection, but I do not understand
the results. My understanding is that for ortho projection, the z-buffer
values are scaled linearly with distance. I am using a Onyx/RE2, Performer
2.0, Irix 5.3 and Iris GL.

I thought that if my near clipping plane is at 8000 and my far clipping plane
is at 12000 and my object is at 10000, then my z-buffer value should be
(2^24)/2 or 7fffff. This is not the case, and I get numbers more like ffbff0.

Is the z-buffer scaled non-linearly in ortho projection (like perspective
projection), or am I doing something else wrong? If it is scaled
non-linearly, does anyone know the algorithm?

Thanks,
Shawn

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