hoberoi@eagle.wesleyan.edu (04/11/91)
hi, I was wondering if anyone had written a routine for doing transparent surfaces using GL on the RS6000 ?. This machine comes without an alpha plane. I remember seeing something on transparent surfaces sometime back... any pointers ?. (my system is an RS6000 530, 24 bit 3D graphics adapter with z-buffer) thanks himanshu
alain@paris.asd.sgi.com (Alain Dumesny) (04/19/91)
From: hoberoi@eagle.wesleyan.edu
Subject: transparent surface with GL
Date: 11 Apr 1991 08:26:00 PDT
hi,
I was wondering if anyone had written a routine for doing transparent
surfaces using GL on the RS6000 ?. This machine comes without an alpha plane.
(my system is an RS6000 530, 24 bit 3D graphics adapter with z-buffer)
You donnot need the alpha bit planes to do transparency (only to store
transparency parameter values, i.e. alpha values). This has been a long time
confusion because of fautly documentation.... In order to do transparency you do
need to have the blending() function available on your machine, which is not
available on PIs and therefore probably not on your system..
use getgdesc(GD_BLEND) (get graphic description) to see if color blending is
available, in which case you simply specify the transparency of an object as just
another material property (like ambient, diffuse, etc..). If you want to fake
transparency on a PI, then you will have to define patterns which represents level
of transparencies, and use setpattern() to use those patterns when drawing. This
works pretty well, but beware of artifacts (because the patterns are onyl 32x32).
Hope this helped...
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Alain Dumesny alain@sgi.com (415)335-7250 Silicon Graphics Inc.
``Read my MIPS -- no new VAXes!!'' -- George Bush after sniffing freon