[xmonad] How to manage three monitors on two graphics cards?

[Norbert Zeh]

Wolfram Kahl [2012.01.05 1353 -0500]:
> I have a machine with two graphics cards,
> and three differently-sized monitors (at different orientations)
> driven by the two cards.
> 
> As far as I could easily find, my main options appear to be:
> 
> (1) In xorg.conf ServerFlags:
>        Option    "Xinerama" "false"
> 
>     Then I have two screens, :0.0 and :0.1;
>     I follow the gentoo Multihead instructions at
> 
>       http://en.gentoo-wiki.com/wiki/X.Org/Dual_Monitors
> 
>     and start X without session manager, just with startx,
>     and have xmonad on the last line of .xinitrc.
>     (This is xmonad-0.10.)
> 
>     That xmonad then appears to manage only the first screen, :0.0,
>     which happens to have two outputs associated with it.
>     (While I had the second card deactivated,
>      xmonad managed these two outputs separately as it should.)
>     However now, even though xrandr still sees these two outputs
>     associated with the current screen,
>     xmonad manages them as a single unit --- does that qualify as a bug?

I'm not sure about this, but I would suspect that this is an x server/graphics
driver issue.  xmonad can only work with what the x server/graphics driver
reports as the available screens.  I had a similar situation where, using three
screens and the NVIDIA proprietary driver.  I was running xinerama on top of
twinview and suddenly had the twinview screens used as a single screen.

In any case, running with "xinerama" "false" doesn't seem to be the way to go
because you can't move windows between independent displays, etc.

> (2) In xorg.conf ServerFlags:
>        Option    "Xinerama" "true"
> 
>      Now xrandr does not work anymore, and xmonad sees one big area.

Indeed, xrandr and xinerama are incompatible.  Do you need xrandr?  From your
post, I suspect that the only reason you want it is that your xinerama setup
still reports everything as one big screen, which is really strange.  Can you
maybe post your entire xorg.conf file (or better put it into a paste service and
post the link here).

Cheers,
Norbert