[ltp] External screen with free drivers

[Marius Gedminas]

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On Tue, Sep 06, 2005 at 11:28:51AM +0200, Paul RIVIER wrote:
> my laptop is a T42 / ATI 9600 M10 / xorg 6.8.2

I have T42 / ATI Radeon Mobility M7 LW [Radeon Mobility 7500] / xorg 6.8.2

> I want to use an external display (for a beamer presentation for exemple)=
 :
> - in "replicator" mode (diplay same thing on both diplays)
> - with separated resolutions (native 1400*1050 for my laptop LCD,=20
> default resolution for the external screen)
> - using the free ati / radeon driver.

I have managed to do all of the above (except my laptop's LCD is
1024x768).  Actually, I got the first one completely for free, and had
to do some research to get different pictures on different displays.

My /etc/X11/xorg.conf is at http://mg.pov.lt/xorg.conf

It is more complex than strictly necessary, as I was experimenting with
various configurations and adding them all as different ServerLayout
sections.  There are long comments describing each at the beginning of
the file.  Ask me if something seems unclear.

I now use MergedFB mode, which seems to be the best one available *if
you use the same resolution on different displays*.  It goes like this:

  1. Connect external monitor
  2. Kill the X session (and GDM)
  3. startx -- -layout MergedFBLayout

        External monitor must be connected at this point, or you'll only
        get clone mode (same picture on both displays)

  4. You have a wide desktop, spanning two monitors

  5. Disconnect external monitor
  6. Press Ctrl+Alt+[+]
  7. You still have a wide desktop, and can scroll it by moving your
     mouse past the edge of the screen
  8. Reconnect external monitor
  9. Press Ctrl+Alt+[+]
  10. You have a wide desktop, spanning two monitors (again)

Alternatively

  6. Run 'xrandr -s 1'
  7. You now have a single desktop
  8. Reconnect external monitor
  9. Run 'xrandr -s 0'
  10. You have a wide desktop, spanning two monitors (again)


If you want different resolutions on different monitors, you can use

  3. startx -- -layout XineramaLayout

but then if you disconnect the external monitor, part of your desktop
will be invisible.  Neither Ctrl+Alt+[+] nor xrandr work in this
configuration.


It is possible to get different resolutions on different monitors with
MergedFB, but then one of the monitors will be a viewport to a larger
virtual desktop (up/down scrolling at screen edge).  It might be
possible to change the driver to disable this scrolling:
  http://bugs.xfree86.org/show_bug.cgi?id=3D276#c144


If you never want to move windows from one screen to another, you can
use

  3. startx -- -layout TwoHeadLayout

Then you get two completely independent desktops -- only the mouse can
move between them.  GNOME doesn't deal with this situation well (panel
applets crash etc.)


Thank you Alex Deucher for implementing MergedFB for Radeons!

Marius Gedminas
--=20
What goes up, must come down. Ask any system administrator.

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