From: Scott Herod (herod++at++rtset.com)
Date: 03/31/2000 09:22:49
Hi Larry,
This is a good problem. I've had a couple of email conversations
with some SGI folks about it before. Basically, as I understand it,
if you have a drawable that can multisample and ask for generic
transparency on an IR you get PFTR_MS_ALPHA transparency. In this
case all geometry is considered opaque ( see the pfChannel man page ).
( I don't think I've tried forcing PFTR_MS_ALPHA_MASK and if I did
don't recall what happened. )
If you want to use PFTR_BLEND_ALPHA transparency, you will need to
break your "X" up into 4 geosets by the branches. Of course if the
arms of the "X" are supposed to move relative to each other, you are
out of luck.
With MS_ALPHA transparency, check that you have a multisample buffer
that is as deep as possible ( probably 8 bit ). Be aware that
transparency gradients will show obvious banding.
There is at least one evil and expensive "trick" that can fix problems.
I can detail it if you are still having problems.
Scott Herod
herod++at++rtset.com
"Larry E. Ramey" wrote:
>
> Lo all,
>
> Does IR graphics cause the Opaque bin and Transparent bin to be
> combined?
>
> Can this problem be solved?
>
> Imagine 2 planes that form an X. Both are slightly transparent. How can
> I draw them so that where one is in front of the other I can see the
> other one behind it, and yet see the same thing when they switch?
>
> The man pages I read seem to imply this is impossible since sorting is
> on a per GeoSet level instead of a perPrimitive basis.
>
> Thanks.
Scott Herod
RT-SET Broadcast Graphics Division Voice : 303-465-1556 x122
100 Technology Drive, Suite 100 FAX : 303-465-2012
Broomfield, CO 80021 USA Email : herod++at++rtset.com
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