dual head howto for xrandr; problem with window manager, no more merged fb or xinerama flags...

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Dear Everybody:

I upgraded an F8 system to F9 and noticed the dual monitors were not
working anymore.  I mean, they were no longer a panorama. They were
clones.

system-config-display does not seem to run on this system. When I try
to use it to turn on dual heads, it just stalls. I mean, If I click
the dual head tab and activate the button, then the program won't
accept an OK click and it will only cancel.

In the X logs, I found that merged FB no longer is supported, and
xrandr is needed to make this work.  I gather that Xinerama is now
deprecated, and we need to make xrandr do the job.   I didn't find any
webpages that told me exactly what I needed, but stumbled to the
solution.

So I had to do some digging about xrandr.

In a terminal, you type

$ xrandr

You see the list of video outputs (monitors?) the system knows about,
on mine they are DVI-0 and DVI-1.  Some people report they see "LVDS"
or "VGA".

If you want to test your system out, you can experiment with xrandr
from the command line.  The syntax to take the two devices I see,
DVI-0 and DVI-1, and put them side by side, is basically like this

$ xrandr --output DVI-0 --mode 1280x1024 --output DVI-1 --mode
1280x1024 --right-of DVI-0

If xrandr works at all with your system, you should see the screen
resize and the workspace stretches across 2 screens.

Some people, who are silly in my opinion, say the user should put that
command in their startup scripts.  It seems better to me to put it in
the xorg.conf.  I'm attaching a working xorg.conf.  The required
changes concerned declaring the two monitor devices in relation to the
xrandr names for them, DVI-0 and DVI-1, and then setting the Screen
attribute to have a wide virtual size and refer to the first device.

Here is the problem I have not solved yet.  I do see a workspace that
is 2560x1024 and can drag applications across the 2 monitors.
xdpyinfo gives the "right answer"--one big workspace

screen #0:
  dimensions:    2560x1024 pixels (676x270 millimeters)
  resolution:    96x96 dots per inch
  depths (7):    24, 1, 4, 8, 15, 16, 32
  root window id:    0x7d

However, I cannot find a window manager that is able to treat the
whole workspace as one big space.  In Metacity (under Gnome), it seems
to see a dividing line between the two monitors.  The panel is limited
to the first monitor.  In the previous xorg, this was a problem as
well with Xinerama or whatever.  There were tricks that were used to
make the window manager see the whole desktop.  For example, for the
radeon merged frame buffer that I used to use in this particular
machine, the option that helped was:
	Option	    "MergedXinerama" "FALSE"

And for the WindowMaker, with an Nvidia card and the nvidia
proprietary driver, the option was:

	Option	    "NoTwinViewXineramaInfo" "true"

In the XrandR documentation, I can't see a similar option.

I hope my advice and xorg.conf help you make the first step, and I
also hope you can help me with this last step.


-- 
Paul E. Johnson
Professor, Political Science
1541 Lilac Lane, Room 504
University of Kansas

Attachment: xorg.conf
Description: Binary data

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