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

[Mike Meyer]

On Thu, 5 Jan 2012 20:31:59 -0500
Wolfram Kahl <kahl at cas.mcmaster.ca> wrote:
> On Thu, Jan 05, 2012 at 05:08:29PM -0800, Mike Meyer wrote:
> > On Thu, 5 Jan 2012 19:16:28 -0500
> > Wolfram Kahl <kahl at cas.mcmaster.ca> wrote:
> > > On Thu, Jan 05, 2012 at 03:53:47PM -0400, Norbert Zeh wrote:
> > > I am running to equal ATI cards with the radeon driver.
> > > 
> > > > > (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?
> > > I just knew no other tool that produces that kind of
> > > information...
> > 
> > Xrandr is the preferred solution. Xinerama has missing functionality
> > and vague specs.
> 
> However:
> 
>  * With Xinerama on, xrandr is not available.

That doesn't seem right.  Both systems I have available have both the
xrandr and xinerama extensions working in the X server. At least, I
can query the screen info using either extension. What makes you say
this?

>  * With Xinerama off, I have two displays,
>    and it appears that not only xmonad cannot move windows between
> the two.

That's standard X behavior. It takes an extension to let you move
windows between multiple screens. It's not clear that xrandr supports
multiple cards. I've certainly never done it.

> > [...]
> > > 
> > > Right now, with Xinerama off, I get:
> > > On DISPLAY :0.0:
> > >  $ xrandr
> > > Screen 0: minimum 320 x 200, current 3968 x 1200, maximum 8192 x
> > > 8192 DVI-0 connected 1920x1200+2048+0 (normal left inverted right
> > > x axis y axis) 495mm x 310mm 1920x1200      59.9*+
> > > DVI-1 connected 2048x1152+0+0 (normal left inverted right x axis y
> > > axis) 510mm x 287mm 2048x1152      59.9*+
> > >    ...
> > >  $ ghc -e "Graphics.X11.openDisplay [] >>=
> > > Graphics.X11.Xinerama.getScreenInfo" Xlib:  extension "XINERAMA"
> > > missing on display ":0.0". [Rectangle {rect_x = 0, rect_y = 0,
> > > rect_width = 3968, rect_height = 1200}]
> > > 
> > > I consider this as wrong and would expect two separate rectangles
> > > to be reported for the two outputs DVI-0 and DVI-1.
> > > (That was probably the case while the second card was
> > > deactivated.)
> > 
> > This is correct for an xrandr config.
> 
> I wanted to say, more precisely, that I consider the output of
> Graphics.X11.Xinerama.getScreenInfo to be either wrong,
> or inappropriate for xmonad to base its screen subdivisions on.

Ah, right. yeah, the ghc output is wrong.

The solution seems to be to list the two outputs on the one card as
different devices, at least according to this:

https://bbs.archlinux.org/viewtopic.php?id=115596

    <mike