transparent surface with GL

[Alain Dumesny]

  From: hoberoi at 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... 

-------------------------------------------------------------------------
Alain Dumesny	alain at sgi.com	(415)335-7250	    Silicon Graphics Inc.

  ``Read my MIPS -- no new VAXes!!'' -- George Bush after sniffing freon