From: phowe++at++csc.com.au
Date: 05/16/2001 21:34:07
Hi,
I'm wanting to read back values from the Z-buffer using glReadPixels and
I have found I'm getting different values on an Octane2 compared to an
Oynx2 and an O2. What I'm doing is using gluProject to convert a point
in world space to screen space, and compare it with what gets read back
from the Z buffer (to determine if the point is occluded by another
object).
On an Oynx2 and O2 the values match (more or less), but on an Octane2
they are completely different. Now I have determined that the cause of the
issue is due to the fact that we change the projection matrix to
orthographic
before the call to glReadPixels. If the call to glReadPixels is made before
the projection matrix is changed, the values match.
Does anybody know what is happening here, does the glReadPixels call
use the projection matrix for converting the Z value somehow in openGl 1.2
verses 1.1 ? Is there away to avoid this?
The man pages mentions on option GL_DEPTH_COMPONENT24_SGIX,
which I tried using but it gave me the same result.
The tech spec on the Octane2 mentioned it has a24bit eye space Z buffer.
What does that mean? Is that different to the Oynx2?
Any Information would be appreciated.
Thanks
Peter
This archive was generated by hypermail 2b29 : Wed May 16 2001 - 21:45:16 PDT