Re: copy z-buffer with scaling on iR

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Hansong Zhang (zhangh++at++cs.unc.edu)
Mon, 20 Oct 1997 21:01:06 -0400 (EDT)

Thanks Rob. Problem nailed.

> Are you using IrisGl or OpenGL ?

OpenGL

> Do you have latest iR gfx patches ? ( 1808 for Onyx, 2191 for Onyx2 )

I don't know. Have to ask the facilities.

> Does it work with no zoom ? ( or other values of zoom )

Yes. 512x512 -> 512x512 copy is no problem.

> Does glCopyPixels return any GL error ? The quick/easy test would be just run
> it through ogldebug and turn on GL error checking. If OpenGL thinks you did a
> GL_INVALID_OPERATION say it might just not transfer any pixels and carry on.

No error message. I have glGetError() etc in my program but caught
nothing.

> Do you have zbuffering etc enabled when you do the copy ?

DEPTH_TEST is off. Turns out this is the problem. So on iR if there's no
DEPTH_TEST, there's no depth write. Generally I think this is not quite
right - no DEPTH_TEST should mean writes without any condition
(i.e. not_depth_test = do_depth_test && depth_func_is_ALWAYS), just like
on Impacts. And what about depth reads? Does turning off DEPTH_TEST
prohibits depth reads (sounds even more unreasonable)? have to try this..

Anyway, the convention should at least be the same across machines.

> Do you have a multisampled visual ( and so a multisampled zbuffer ) ?
>
Turning GLUT_MULTIPSAMPLE on or off (I use glut) doesn't make a
difference.

Thanks,
Hansong

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