From: Angus Dorbie (dorbie++at++sgi.com)
Date: 05/24/2000 14:52:29
Thanks, I tried to put out a correction in a followon post.
On the stereo issue, the attempt was not to get direct stereo support
from the card but to use two independent channels to produce stereo. So
stereo support at the card/driver level is not really the issue in this
scenario. The sync I was referring to is not of swap to vertical retrace
but the genlock across eyes and the equivalent of swapready. In this
instance given that you can't genlock, deliberately not syncing to
vertical retrace may be a better option since you will need some kind of
handshake between draw processes. Without genlock this could introduce a
significant delay with swap sync to refresh, and the stereo artifacts
aren't necessarily worse in either scenario.
Cheers,Angus.
Tom Flynn wrote:
>
> On Wed, 24 May 2000, Angus Dorbie wrote:
>
> > This cannot work with a single app right now.
> >
> > It might be possible by running two copies of Performer as separate
> > applications but you need DRI based drivers to handle the dispatch of
> > OpenGL to the right card with this type of config
>
> slight correction here...currently neither DRI or Nvidia drivers handle
> multiple cards. Both drivers are designed so that such a thing could be
> possible, but it has yet to be implemented.
>
> > and the nVidia drivers
> > don't use that framework but use their own fast dispatch method so you'd
> > need to mess around with which different version of OpenGL libs that the
> > two copies of Performer linked to so that the nvidia display got
> > hardware acceleration via the SGI nVidia drivers and the voodoo's (SLI I
> > assume) worked via the DRI drivers.
> >
> > This is my best guess as to what you need to do, I haven't tried this, I
> > expect you'll be the pioneer if you proceed with your plan.
> >
> > The stereo will be horrid since there will be no sync of refresh, swaps
>
> I don't believe stereo is supported in either driver at this time. As to
> swap on vertical retrace, that can be enabled via an environment variable
> (GL_SYNC_TO_VBLANK) on our 230 systems. I don't believe the DRI driver
> currently supports swap on vertical retrace.
>
> > or update. You could do a little bit in software through shared memory
> > but you's will at least like to block on frame completion before the
> > swap probably just after pfDraw and that will slow you down.
>
> This really needs to be done inside the driver where you can have control
> over when data gets sent down the FIFO. You might be able to fudge
> something using the SYNC extension to XFree86, but it might be
> difficult to make sure OpenGL is sync'd as expected. Again, this should
> really be done in the driver.
>
> tom
> --
> "Mongooses are famous for their snake-fighting ability, and are
> almost always victorious because of their speed, agility, and timing
> and also because of their thick coat."
-- For Performer+OpenGL tutorials http://www.dorbie.com/"In the middle of difficulty lies opportunity." --Albert Einstein
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