Friday, 18 January 2013

Optimus and Ubuntu 12.10 (Part 4)

This post is the fourth of a series of posts on tweaking Ubuntu 12.10 to exploit Optimus technology on my Lenovo W530 to the extent I need. Make sure you are familiar with the context, especially the objectives and constraints as described in Part 1, Part 2 and Part 3.

Moving windows from the primary screen to the external VGA screen

As it has been explained before, windows cannot cross screen boundaries, and the GNOME desktop cannot span multiple X screens even in the case when the these screens belong to the same display (X instance). It should be obvious that this is also the case with screens that belong to different X servers.

The objectives defined in the previous parts require the ability to extend the GNOME desktop to the monitor attached to the external VGA port, to run presentations using two monitors and to clone the primary monitors content to the external monitor.

In order to meet one of the objectives, one could mirror, or better said clone the content of one screen to another screen. To be even more precise, only a given portion of the screen has to be cloned to other viewport, the area of the other screen that is displayed by the external monitor. There is a userspace tool called hybrid screenclone to perform exactly this task - find more on this tool below.

Extending the desktop to a screen of the other X server

Thinking further, in order to be able to extend the desktop and thereby meet other objectives, one could set up a mock monitor in the first X server, and then, clone the content to the screen of the other X server so it would show up on the external monitor.

My first approach was to examine the video outputs of the integrated graphics device, and found VGA[12] that is wired to /dev/null (see Part 2). With various xrandr commands I could force the unused, thus always disconnected output to be configured with a fixed resolution, right of the primary monitor. A screenshot confirmed I was half way through: it contained a black are next to the primary desktop. I could even drag windows onto this black area, however, the desktop would not extend to this portion of the X screen. Also, libreoffice refused to start the slideshow in multi-monitor mode, as it only detected one connected monitor. While the idea was not completely useless, this approach did turn out not to be usable in production.

A bit of googling revealed, that the author of hybrid screenclone also maintains a patch against the intel video driver which adds a dynamically configurable virtual output - enabling exactly the scenario I was targeting.

Intel driver hack

The listing below takes the reader through the process of creating and installing a package containing the patched version of the intel video driver.

$ mkdir /tmp/foo && cd /tmp/foo # we are going to compile in tmpfs/RAM
$ sudo aptitude build-dep --schedule-only  xserver-xorg-video-intel
$ sudo aptitude # review interactively what is going to be installed
$ apt-get source xserver-xorg-video-intel
$ cd xserver-xorg-video-intel-2.20.9/
$ wget
$ # the newer patch did not match.
$ patch -p1 < xserver-xorg-video-intel-2.20.2_virtual_crtc.patch
$ # now update the version to show this is a patched package
$ # NEVER alter packages without making it clear in the package version!
$ # I prepend this to debian/changelog:
$ mv debian/changelog debian/changelog.old && cat <<EOF > debian/changelog
xserver-xorg-video-intel (2:2.20.9-0ubuntu2+virtual-crtc) quantal; urgency=low

  [ Tibor Bősze ]
  * Add xserver-xorg-video-intel-2.20.2_virtual_crtc.patch

 -- Tibor Bősze <>  Sun, 13 Jan 2013 03:15:00 +0200

$ cat debian/changelog.old >> debian/changelog && rm debian/changelog.old
$ # now build and install the package
$ dpkg-buildpackage -b
$ sudo dpkg -i ../xserver-xorg-video-intel_2.20.9-0ubuntu2+virtual-crtc_amd64.deb
$ # as you see, the package version will clearly show that this is a patched package
$ # prevent the package to be automatically updated
$ sudo aptitude hold xserver-xorg-video-intel

After a reboot, the command below will active the virtual monitor. The graphical display manager will not show any second display, however, creating a screenshot quickly confirms that the second virtual monitor is active, and the desktop correctly extends to it. Also, libreoffice impress can finely use it for running the slideshow in dual monitor mode.

$ xrandr --output LVDS2 --auto --output VIRTUAL --mode 800x600 --right-of LVDS2


To render this post complete, below are listed the commands to download and compile the tool.

$ # we are still doing stuff in tmpfs/RAM
$ aptitude install git-core
$ git clone git://
$ cd hybrid-screenclone && make
g++ -std=c++0x -g -Wall  -lpthread -lX11 -lXdamage -lXtst -lXinerama -lXcursor -o screenclone fatal error: X11/Xcursor/Xcursor.h: No such file or directory
compilation terminated.
make: *** [screenclone] Error 1
$ apt-file search Xcursor.h
libxcursor-dev: /usr/include/X11/Xcursor/Xcursor.h
$ aptitude install libxcursor-dev
$ make
g++ -std=c++0x -g -Wall  -lpthread -lX11 -lXdamage -lXtst -lXinerama -lXcursor -o screenclone fatal error: X11/extensions/Xinerama.h: No such file or directory
compilation terminated.
make: *** [screenclone] Error 1
$ aptitude install libxinerama-dev libxdamage-dev libxtst-dev
$ make
$ mv screenclone ~/optimus/

By default the tool will clone the first screen of the first display to the first screen of the second one, that is, :0.0 to :1.0. This almost completely fits my use case, I added the parameter -x 1 which limits the content to be copied to the area of the screen that is displayed by the second monitor, the VIRTUAL output in my case.

$ # clone the viewport of the VIRTUAL output from :0.0 to the top left corner of :1.0
$ ~/optimus/screenclone -x 1 

Part 5 will revisit the issue of changing framebuffer number assignment and provide a more elegant solution to fixing usplash.


  1. small typos:
    * debain => debian,
    * add an empty line before "-- Tibor Bősze..."
    * apitude => aptitude