[Mesa3d-users] Problems with glDrawPixels and glReadPixels

[Ross G. M. <rg...@cs...>]

Hello All,
	I need some help with a program that uses glDrawPixels and 
glReadpixels to write to and read from the depth buffer.  Specifically, 
when I write data to the depth buffer using glDrawPixels and subsequently 
read it back out with glReadPixels I get different results.  Between half 
and two-thirds of the pixels are correct (not counting the background), 
but the remainder are off slightly.  In fact, their integer values are one 
less than they should be.  This isn't much, but it's enough to keep parts 
of subsequent polygons from being displayed because the depth buffer is 
wrong. 

I didn't want to post a huge message to this list, so I've created a web 
page that goes into further detail and includes a short program that 
demonstrates the problem.  It also has a couple of screen shots.  The 
page is available here:

http://cs.baylor.edu/~rgm/mesa/drawpixels.html

If anyone could tell me what I'm doing wrong, I'd appreciate it.

Thanks,
-Ross