Jenny Zhao (zhz++at++dandan.asd.sgi.com)
Tue, 1 Oct 1996 11:32:21 -0700
To: "Jenny Zhao" <zhz>
cc: dorbie++at++bitch.reading.sgi.com
Subject: Re: (Fwd) Re: Final word on reading the Z-buffer in Performer 2.0
Date: Tue, 01 Oct 1996 11:29:49 -0700
From: Ziv Gigus <ziv++at++argus>
"Jenny Zhao" writes:
>
> hi, ziv,
>
> there is much confusion about whether
> we could read the depth value on
> machines with multisampling visual.
> could you please help us
> clarify it?
> i have included below the email
> from info-performer on this subject.
IrisGL:
You
CAN NOT
read the multisampled Z buffer.
To get depth information you do have to allocate a non multisampled
depth buffer (zbsize(>0)) and draw with multisample(FALSE). Note that
drawing/clearing with multisample(TRUE) will not effect the non
multisampled depth buffer and drawing/clearing with multisample(FALSE)
will not effect the multisampled Z buffer.
OpenGL:
Running on Irix 5.3+patch918 (but not in 5.3 or 5.3+patch154) or Irix 6.2
you
CAN
read the Z buffer of a multisampled visual.
The value that you get is the depth stored at sample 0 of the pixel.
Note, that you DO NOT have to turn multisampling off, nor do you have
to redraw the scene.
Note, also that in OpenGL you can either have a multisampled visual
with a multisampled Z buffer, or a non multisampled visual with a non
multisampled Z buffer. When using a multisampled visual, the same z
buffer is used both when multisampling is on or off.
Finally note that spec does not require the implementation to return
the value of sample 0; the implementation is free to return the value
of any of the samples or a reasonable function (i.e., min, max, mean)
of the depth values of all samples. However, both RE and IR return
the value of sample 0.
> thanks!
>
Ziv
..............................................................
Ziv Gigus M/S 7U-553
Silicon Graphics Computer Systems email: ziv++at++sgi.com
2011 N. Shoreline Blvd. voice: (415) 933-2869
Mountain View, CA 94039 fax : (415) 965-2663
---End of forwarded mail from Ziv Gigus <ziv++at++argus>
--
Jenny Zhao zhz++at++asd.sgi.com 415 933-5091 (Voice) 415 965-2658 (Fax) Silicon Graphics - IRIS Performer ======================================================================= List Archives, FAQ, FTP: http://www.sgi.com/Technology/Performer/ Submissions: info-performer++at++sgi.com Admin. requests: info-performer-request++at++sgi.com
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