Discussion:
State of OpenGL Xinerama as of 2014
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Coyo
2014-07-26 21:09:21 UTC
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I want multiple displays, as many as 24 heads, and a single OpenGL
application spanning all of them as though they were one display. Is
this possible with current Linux support?

I want to know because I want to put together a Linux gaming rig.
It'll have custom refrigeration and independent power and everything,
but it has to run Linux and it has to run at full capabilities. I want
to be 100% sure it'll work before I plop down all that money.

AMD has cooked up something called Eyefinity and has been pushing this
proprietary tech over YouTube and its own website, but this confuses
me. Hasn't Linux been doing this for years?

I've heard mixed reports. Some say that one OpenGL application can
trivially use multiple monitors in Xinerama mode, while others say
that OpenGL acceleration will only work on the primary display, though
non-OpenGL applications can occupy other monitors.

The way AMD marketed Eyefinity seems to make the assumption that
OpenGL applications previously could not span more than one display.
It is also assumed that previously, multiple GPUs in CrossfireX or SLI
mode were not supported with Xinerama.

I'm aware that support for this in the radeonsi and nouveau open
source drivers are nonexistant, but what about the propietary drivers?
I've done some research, but I figured asking wouldn't hurt.

I was taught that there was no such thing as a dumb question.
Freenode's attitude flies in the face of that, linking people who
actually put in an effort to http://lmgtfy.com/ which is very
insulting. Kinda reminds me of Rick Burns Your Company's Computer Guy.

There's a reason no one likes him.

Anyway, I thought I'd ask because I'm getting conflicting reports. I
don't want to sink tens of thousands of dollars into a Linux gaming
box if the fundemental design completely fails to function.

Will multiple displays, multiple GPUs, single OpenGL application work
on Linux?

Thank you very much for your time and patience with me. Any time and
patience you spend on me is greatly appreciated.
Alberto Luaces
2014-07-28 09:29:44 UTC
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Coyo writes:

> AMD has cooked up something called Eyefinity and has been pushing this
> proprietary tech over YouTube and its own website, but this confuses
> me. Hasn't Linux been doing this for years?

Indeed, I have been using accelerated OpenGL on two monitors with either
Xinerama or X displays without problems. And here you can see a much
bigger and older setting:

https://www.cs.uaf.edu/2007/powerwall/

From what I have just read, the point of Eyefinity is to be able to
drive 6 monitors at once with just only one card, while the typical
output number of a vanilla card is two:

https://superuser.com/questions/95884/ati-eyefinity-under-linux

The question is now, apart from the convenience of having to use less
cards, what is the performance drop to be expected against the
traditional solution? It seems like a convenience vs. speed trade-off.

Note that is not my aim to take part into this matter.

--
Alberto
Nobody
2014-07-29 23:11:15 UTC
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On Sat, 26 Jul 2014 16:09:21 -0500, Coyo wrote:

> I've heard mixed reports. Some say that one OpenGL application can
> trivially use multiple monitors in Xinerama mode, while others say that
> OpenGL acceleration will only work on the primary display, though
> non-OpenGL applications can occupy other monitors.

OpenGL can typically be used on Xinerama displays provided that all of the
video cards use the same driver (i.e. same vendor and hardware "family").
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