TwinView incorrectly indicates Xinerama as off when using two cards

[ebf]

Hi,

I am experiencing a similar problem as reported in an earlier thread:

http://www.nvnews.net/vbulletin/showthread.php?p=946340

My setup is as follows:

GeForce 7600 GS, with two attached 17" LCD displays
GeForce FX 5200, with one attached 17" LCD displays
NVIDIA 1.0-9755 drivers

I've also attached an nvidia-bug-report.log.

When I have just the first case (7600 GS) enabled, I can get both displays working fine. TwinView reports Xinerama as enabled, as the following output (from the xinerama-test.c file, which I've attached) indicates:

Version 1.1
ErrorBase = 0, EventBase = 0
Xinerama is active
2 screens
0) 1024 x 1280 @ (1024, 0)
1) 1024 x 1280 @ (0, 0)

Indeed, my window manager can place and maximize windows, recognizing the display edges.

However, when I also enable the second card (FX 5200), TwinView apparently reports that Xinerama is not active, though it still does provide the correct information for the two displays on the first card:

Version 1.1
ErrorBase = 0, EventBase = 0
Xinerama is not active
2 screens
0) 1024 x 1280 @ (1024, 0)
1) 1024 x 1280 @ (0, 0)

It appears that the drivers are incorrectly returning false from XineramaIsActive when there are two cards enabled. I am thus nearly certain that this is an issue with the drivers, and not with the window manager.

Thanks,

Eric

[AaronP]

Hi ebf,
This is the intended behavior. Some applications get confused if the Xinerama extension reports Xinerama enabled and there is more than one X screen.

[ebf]

Aaron,

I see. Is there any way to disable this behavior? I imagine from your response that while some applications do get confused, other applications do not get confused.

If so, it would be useful if I could control whether XineramaIsActive returns true or false in this case. Might NVIDIA support this as an option in a future release, or is there a simple fix?

Thanks for your reply,

Eric

[netllama]

You might want to check the driver README's discussion of the NoTwinviewXineramaInfo option.

[ebf]

Hi netllama,

Thanks for your reply.

Actually, my problem is the opposite of what is solved by the NoTwinviewXineramaInfo option. Specifically, I want TwinView to provide the Xinerama information, but when I am using multiple GPUs, TwinView does not do this.

I would like some way to force TwinView to provide this information, so that my window manager would take advantage of it. Any thoughts?

Eric

[netllama]

I'm afraid that I don't have any suggestions. This sounds like a limitation of your window manager.

[ebf]

netllama,

Thanks again for your reply.

I don't understand why you would suggest it is a limitation of the window manager. If TwinView is indicating that Xinerama is not active, then why would a program continue to ask for Xinerama information?

That is, it seems quite reasonable that a program would be written as follows:

if (XineramaIsActive(display))
{
   // Xinerama is enabled, so get information
   info = XineramaQueryScreens(display, &num);
   ...
}
else
{
   // Xinerama is not enabled, so can't get information
}

But if TwinView is returning false for XineramaIsActive, then such a program will come to the wrong conclusion. Do you really view this as a bug in the program, and not in the drivers?

Thanks,

Eric

[netllama]

As Aaron stated, this is expected driver behavior, its not considered a bug. At best it would be considered an enhancement request in the driver. I could certainly open one if you'd like, however there is little demand for this change in functionality.

[ebf]

Yes, if you could open an enhancement request, I would appreciate it.

As for demand, there are at least two other instances:

http://www.nvnews.net/vbulletin/showthread.php?p=946340

http://www.nvnews.net/vbulletin/showthread.php?t=72869

Thanks,

Eric

[JaXXoN]

Hi!

I have seen that you didn't enabled xinerama in your xorg.conf.
This is ok for a twinview setup, because the nvidia xinerama extension
is enabled by default, providing the appropriate information
(unless disabled with NoTwinViewXineramaInfo).

If you add another screen with a second card, then TwinViewXineramaInfo
is disabled - AFAIK, it is currently not possible to have Xinerama only for a
subset of screens.

To truely form three separate screens, you need to define two
screen for the first card as described in chapter P ("Configuring
Multiple X Screens on One Card").

If your WM is not capable of handling separate Screens then you
need to apply the option "Xinerama" "on".

If you like to use all three displays with xinerama, but you are
not happy with the XineramaInfo because of TwinView, then
you may like to read the following post:

http://www.nvnews.net/vbulletin/show...7&postcount=10

regards

Bernhard

[ebf]

Bernhard,

Thanks for the detailed reply! My situation is complicated somewhat since I rotate my displays using the XRandR extension. While it is possible to have both TwinView and XRandR enabled, as far as I know it is not currently possible to have both Xinerama and XRandR enabled.

Thanks also for the reference to the patch. I think I will first try modifying the source of my window manager, but if that doesn't work, then I'll try the patch.

Eric

[AaronP]

ebf,
If you don't mind giving up the ability to rotate on the fly, you can use the "Rotate" option in xorg.conf to rotate individual screens in Xinerama.