Screen settings

DoudouLinux is featuring a tool to change the screen resolution and set which screen is on or off when 2 screens are plugged. Its interface varies depending on the number of connected screens. Usually on a desktop computer, there is only one connected screen and you will just be offered to set the screen resolution and refresh rate [1]. On a laptop you may want to have both the laptop screen and an external screen connected. In this case the interface is a little more complicated since you will be able to set each screen resolution and refresh rate independently, as well as which screen is active or not.

Case of a single screen

The tool to set the screen is located in the group “System” of the “Tune” tab. DoudouLinux is supposed to set a correct resolution at boot, this is why this tool is not directly placed in the “Tune” tab. Refer to the paragraph “Screen tuning algorithm at boot” below for further information about how screens are set at boot. The tool in case of a single video output is very simple:

Screen settings with a single display

Changes can be applied on the fly. The only drawback is that they are not saved when you leave the activity even with persistence activated, this is a known issue. Please also note that not all resolutions of your screen may be available. As explained below, DoudouLinux is selecting resolutions that are comfortable for the user and not too large, typically below 1280×1024 [2].

Case of two screens

If you start DoudouLinux with two screens plugged, DoudouLinux should automatically detect them and set a resolution fitting well on the external one (supposing that you are using a laptop). The screens will show or try to show the same thing if their resolution cannot be identical. Entering the activity “Whole DoudouLinux” you will be able to start the screen setting tool. This time the interface is a little more complicated. You are given the following options:

• switch on or off a screen, in the first tab
• set a different resolution on each screen, in the second tab

Please note again that settings will not survive after activity exit, even with persistence activated.

Screen settings with 2 displays: which one is on/off

Screen settings with 2 displays: screen parameters

Note also that, if you plugged a large LCD TV-set in your laptop, it may happen that its characteristics are not correctly detected, which may lead to very small and unreadable characters in texts. Unfortunately we still cannot propose an easy solution for these cases. If you do not have Linux skills, the only solution is to use the activity “Whole DoudouLinux” only. Just:

 unplug the TV-set from your computer
 press Ctrl+Alt+Backspace
 wait for the menu of activities to show again
 replug the TV
 enter the activity “Whole DoudouLinux”

You are then able to use the screen setting tool to activate both screens using the laptop display settings, but as soon as you leave the activity, the issue is back…

Screen tuning algorithm at boot

The algorithm used to automatically tune the screen settings when DoudouLinux is starting is the following:

• If the screen is detected as a CRT screen (monitor with a tube)
  • DoudouLinux reads the monitor and graphic card characteristics
  • whenever available, a refresh rate above 70Hz is forced
  • the largest resolution below 1280×1024 for the selected refresh rate is set
• If the screen is detected as an LCD screen (LCD display or laptop screen)
  • the native screen resolution is chosen
  • refresh rate does not matter since these screens are not blinking as much as CRT screens

Please note that it may happen that an LCD display is not detected as an LCD display. This is why you may get a smaller resolution (ie. 1280×1024) than the native one on some LCD displays. In this case it is not possible to change the resolution to a larger one with the screen setting tool. You need to do a technical operation directly in the screen configuration file, as detailed below.

Manual tuning

If you have Linux skills, you can change the screen configuration file named /etc/X11/xorg.conf in order to match your needs. Changes in this file are saved only if you have activated any data persistence. Moreover a hardware signature feature in DoudouLinux allows to always use the same configuration file for a given computer, even if you are regularly using DoudouLinux on computers with different hardware configurations.

Removing the screen resolution limits

If you are using an LCD monitor and DoudouLinux is not using its native resolution, you certainly need to remove screen resolution limits. In the file /etc/X11/xorg.conf, the following lines are defining the allowed screen resolutions:

	SubSection      "Display"
		Depth   24
		Modes   "1280x1024" "1152x864" "1024x768" "800x600" "640x480" "400x300" "320x240"
	EndSubSection
	SubSection      "Display"
		Depth   16
		Modes   "1280x1024" "1152x864" "1024x768" "800x600" "640x480" "400x300" "320x240"
	EndSubSection
	SubSection      "Display"
		Depth   15
		Modes   "1280x1024" "1152x864" "1024x768" "800x600" "640x480" "400x300" "320x240"
	EndSubSection

At your convenience, you can either remove them, comment them by adding a number character “#” at each line start, or modify the resolution values. Save and restart the menu of activities by leaving the current activity or pressing Ctrl+Alt+Backspace.

Forcing a correct font size on TV

If you are experiencing very small fonts on your TV set, you can activate a parameter in /etc/X11/xorg.conf which forces the value of the physical screen dimensions. Just uncomment the following line by removing the “#” character:

#	DisplaySize	220 165

Save and restart the menu of activities by leaving the current activity or pressing Ctrl+Alt+Backspace. If the font size is still not correct, you will have to tune the values 220 and 165. They are representing the number of screen dots per inch, the first one for the horizontal direction and the second one for the vertical one. They should match the actual values of your computer screen (not the TV). Increasing numbers should increase font size. Please note that we arranged the values to have a ratio 4/3 (220/165 = 1.33), if your screen is 16/9 or so, you may prefer using another ratio.

How to reset the configuration file?

The configuration file is generated while booting; however, when the hardware signature is identical to a previously computed one, the configuration file saved is simply reused and thus not regenerated. If you made changes that are wrong and unrecoverable (you did not use comments to backup the original values?), the only solution is to remove the configuration file then restart the generation tool. You first need to determine what is the configuration file path, since is name depends on hardware signature:

$ ls -l /etc/X11/xorg.conf
lrwxrwxrwx 1 root root 56 2011-02-24 15:16 /etc/X11/xorg.conf -> /home/etc/X11/xorg.conf.f23ee189c503a601e8f515db67dea61b

Here the true file path is:

/home/etc/X11/xorg.conf.f23ee189c503a601e8f515db67dea61b

You have to remove it then to restart the configuration generation tool:

$ sudo rm /home/etc/X11/xorg.conf.f23ee189c503a601e8f515db67dea61b
$ sudo /usr/bin/dexconf

Now restart the menu of activities by leaving the current activity or pressing Ctrl+Alt+Backspace. Everything should be restored!

Changing the video driver

Sometimes the video driver is not correctly detected. This should not happen so much now since DoudouLinux is now trying to guess the video driver for Intel and nVidia video cards; however, in case of failure or if your video hardware is not of these two brands, you can either change the video driver or add it to the configuration file /etc/X11/xorg.conf.

To add your video driver, you can use a dedicated tool simply called “video-driver”. You just need to give the driver name as the first argument:

$ sudo video-driver intel

Note that this tool is only able to add the driver, it cannot change nor remove it. If you want to change or remove it, you need to edit /etc/X11/xorg.conf and modify the following section:

Section "Device"
	Identifier      "Configured Video Device"
	Driver          "intel"
EndSection

Of course you need to know the name of the Linux driver to be used…pre