Angus Dorbie (dorbie++at++multipass.asd.sgi.com)
Fri, 27 Jun 1997 18:41:40 -0700
Most folk who use pbuffers think
"I don't want to see it so I must render off screen"
But much of the time they can draw their stuff to the
normal framebuffer and whatever visible channels they have
will subsequently hide the results, ofcourse by then the
information has been read back to memory or TRAM in a post
draw function.
This would allow you to avoid all this pbuffer nonsense and
avoid wasting framebuffer resources.
Cheers,Angus.
On Jun 27, 8:11pm, Amaury Aubel wrote:
> Subject: Re: Generating textures on the fly
> On Jun 25, 8:05pm, Rob Jenkins wrote:
> > Bit of an aside, there's a chapter of the 6.2 gl_dev relnotes:
> > 'Pbuffers_on_Impact' that anyone wanting to use Pbuffers ( esp on Impact )
> > would find useful.
> >
> > Cheers
> > Rob
> >-- End of excerpt from Rob Jenkins
>
>
> Thanks Rob for pointing this out, it was most useful!
>
> At last I managed to generate textures in an off-screen pbuffer with the
right
> alpha values, load them into TRAM, and map them onto Billboards with
> transparency on. Pew! So I almost achieved my goal except that...
>
> it won't work with a Z-buffered pbuffer!
> (because it runs out of FB resources)
>
>
> On our Octanes and O2s, findvis 'rgba Z' gives:
>
> 0x2b, RGBA 4/4/4/4, db, Z 24, S 8, accum 16/16/16/16
> 0x2d, RGBA 4/4/4/4, db, stereo, Z 24, S 8, accum 16/16/16/16
> 0x2f, RGBA 5/5/5/1, db, Z 24, S 8, accum 16/16/16/16
> 0x31, RGBA 5/5/5/1, db, stereo, Z 24, S 8, accum 16/16/16/16
> 0x33, RGBA 8/8/8/8, db, Z 24, S 8, accum 16/16/16/16
> 0x35, RGBA 8/8/8/8, Z 24, S 8, accum 16/16/16/16
>
> What is the "size" of a pixel in 0x2b, 0x2f, 0x35?
> Even if I allocate a tiny (ie 16x16) pbuffer it crashes...
>
> My hardware config. is the following:
> Graphics board 0 is "IMPACTSR" graphics.
> Managed (":0.0") 1280x1024
> Product ID 0x3, 2 GEs, 2 REs, 4 TRAMs
> MGRAS revision 1, RA revision 0
> HQ rev B, GE11 rev B, RE4 rev C, PP1 rev A,
> VC3 rev A, CMAP rev E, Heart rev D
> 19" monitor (id 0x1)
>
> Channel 0:
> Origin = (0,0)
> Video Output: 1280 pixels, 1024 lines, 72.24Hz (1280x1024_72)
>
> Do I stand any chance to have a Z-buffered (preferably sb) pbuffer?
> Maybe if I change down the screen resolution?
>
>
> Amaury.
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>-- End of excerpt from Amaury Aubel
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