Multihead trouble docs update -- xrandr required for proper display

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What steps will reproduce the problem?
1. Clean FreeBSD install.

2. Install the following ports:
   - x11/hs-X11
   - x11/hs-xmonad
   - x11/xorg-minimal
   - x11/xterm
   - x11/nvidia-xconfig
   - x11/nvidia-settings

3. Configure!
   - Use a vanilla `defaultConfig`
   - Use default config from nvidia-xconfig
   - Set up the second monitor using nvidia-settings, check Xinerama
   - Start the engines.

What is the expected output? What do you see instead?

Should see a working multihead xmonad running. The result is one workspace 
stretched over both monitors. Going through the current troubleshooting FAQ 
doesn't lead to any answers. You'll get the following output:

$ ghc -e Graphics.X11.Xinerama.compiledWithXinerama
True

$ ghc -e "Graphics.X11.openDisplay [] >>= Graphics.X11.Xinerama.getScreenInfo"
[Rectangle {..snip..},Rectangle {..snip..}]

It should mention to make sure you've got xrandr installed. I dunno how obvious 
that is, but it *is* the troubleshooting section!

What version of the product are you using? On what operating system?

$ uname -a
FreeBSD 9.0-RELEASE FreeBSD 9.0-RELEASE #0: Tue Jan  3 07:46:30 UTC 2012     
root@farrell.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  amd64

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.0.4

$  xmonad --version
xmonad 0.10

Are you using an xmonad.hs?  Please attach it and the output of "xmonad
--recompile".

main = xmonad defaultConfig{terminal = "/usr/local/bin/xterm"}

:P

Please provide any additional information below.

Might make more sense to just make the xmonad port depend on X11 and xrandr, so 
they're guaranteed to get pulled in. I'm going to email the maintainer.

Original issue reported on code.google.com by unpan...@gmail.com on 28 Mar 2012 at 5:30

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The X11 package will require Xrandr starting with version 1.6.0 (though the 
only code above there that expects it is the newest xmobar which is still in 
git yet and a module I made that is only in darcs; I don't know what might care 
in xmonad's core).

As an aside, since when does the binary nvidia driver support Xrandr?

Original comment by MathStuf@gmail.com on 30 Mar 2012 at 1:42

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I'm honestly not too sure what xrandr does (anything related to X11 scares me; 
I just need my xterms and web browser) -- but the internet suggests it's been 
compatible with the nvidia blobs for awhile. Anecdotally, it's been working for 
at least 9 months.

That said, having xrandr *installed* seems to be enough, for some reason. It 
doesn't appear to be loaded into X11:

$ xrandr
RandR extension missing

:|

Original comment by unpan...@gmail.com on 30 Mar 2012 at 2:50

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"randr" is a contraction of "Resize and Rotate" which allows you to switch up 
your monitor configuration at runtime (it's outside drivers so that every 
driver doesn't need something like the nvidia-settings GUI). This link[1] might 
be of interest to you.

The driver is probably seeing one screen after the driver maps the two displays 
together. Does your nvidia card have two GPUs?

There also seems to be indications that the nvidia driver might act weird when 
Xinerama and Xrandr are enabled.

[1]https://wiki.archlinux.org/index.php/NVIDIA#Enable_screen_rotation_through_XR
andR

Original comment by MathStuf@gmail.com on 31 Mar 2012 at 12:15

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Nah, it's a single-GPU GTX 560 Ti.

I have Xinerama enabled in my xorg.conf, but not Xrandr. It seems just having 
it installed is enough to make the configuration work; that's enough to make me 
happy. I just wanted to post my troubles/solution somewhere (and maybe get them 
into the official troubleshooting docs) to save the next guy a few hours :)

Original comment by unpan...@gmail.com on 31 Mar 2012 at 12:31

[GoogleCodeExporter]

Ah, this might also be worth it to put on the wiki then.

Original comment by MathStuf@gmail.com on 31 Mar 2012 at 2:22