Originally Posted by AaronP
RandR 1.2 currently only works on a single X screen (a real one, not a Xinerama screen). You can get exactly the same "fakerama" behavior with the nvidia driver today with TwinView. To span multiple GPUs, you still need the real Xinerama extension, which still disables RandR. See hw/xfree86/modes/xf86RandR12.c in the xserver tree:
xf86RandR12Init (ScreenPtr pScreen)
/* XXX disable RandR when using Xinerama */
(PanoramiX is the old historical name for Xinerama).
RandR 1.2 support in the nvidia driver is in the works, but don't expect it to magically make RandR + real Xinerama work.
I won't pretend to be a C programmer but what you just said is contrary to what the developer of XRandR has stated on his blog. It states that XRandR supports Xinerama internally, it says nothing about it only working with a single GPU, furthermore, in my own tests I managed to get output to both monitors (on 2 GPUs) using XRandR 1.2 with Xinerama disabled in xorg.conf, granted they were two seperate desktops but from what I have read (and I have read a lot on this issue for obvious reasons) XRandR's version of xinerama in the new spec gives no indication that this is limited to single GPUs. Without a pair of Intel Graphics Cards I can't confirm either way as to my knowledge only the Intel drivers currently support the new XRandR 1.2 specification (since the person who wrote XRandR 1.2 works for Intel from what I have been able to ascertain). It would be incredibly short sighted to limit this new feature of XRandR to a single GPU and would pretty much make the feature redundant as it would do nothing to solve the problem at hand.
In the modern age more and more people are using multiple GPUs, both with your own SLI system and your competitor's equivalents and this trend is likely to increase as equipment such as displays become less expensive. It would make no sense to start restricting software to single GPU systems in an age where more and people are doing the opposite.
I will send an email to the developer of XRandR 1.2 personally to try and get confirmation on the multiple GPU situation with the new spec. If indeed this is the case, then what would you suggest for those of us who do use multiple GPUs? Are we not permitted to play games or use a PVR or enjoy modern features such as composite window managers? Are we supposed to be excluded and penalised for purchasing additional hardware? By purchasing multiple video cards we are in essence increasing your (and other manufacturer's) revenue multiple times yet our usability and experience is significantly decreased as a result? It seems a little backwards to me.
If this is the case then obviously the situation needs to be addressed and a solution found, as it is in no way conducive of an innovative and evolving industry.
I will get back to you once I have a reply from the XRandR 1.2 developer, but I would request that yourself and your colleagues join the community in trying to find a suitable solution to this situation, not only because it is the logical and sensible thing to do, but because in doing so you will be protecting your own revenue streams instead of limiting them.
I appreciate your input in this thread so far and hope I have not said anything you may find insulting, as that is certainly not my intention, I am merely trying to find a solution to what I and others see as a serious problem with the current implementation of multiple GPUs.
Thanks again for the prompt reply.