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A Linux User Reference

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DESKTOP UIS

Accessibility

  • Technology, terminology
    Sticky keys

    Allows for a key combination like Ctrl+Alt+F9 to be entered sequentially.

    Repeat keys

    Ignore long presses of the same key and control the repeat rate of the key presses.

    Bounce keys

    Ignore repeated presses of the same key.

    Slow keys

    Specify the duration for which you must press-and-hold a key before the system accepts the key press.

    Toggle keys

    Emit an audible notification when a user activates or deactivates a toggle key.

    Mouse keys

    Use the numeric keypad to emulate mouse actions.

    High Contrast/Large Print Desktop Themes

    Implement such themes to aid visual impairedness.

    Screen Reader

    A software application that enables people with severe visual impairments to use a compute. They provide information about icons, menus, dialogue boxes, files and folders.

    Two ways to provide this information:

    • Speech A Text-To-Speech (TTS) engine to translate on-screen information into speech - output through earphones or speakers. Maybe hardware or software.

    • Braille An external hardware device - a refreshable Braille display. Contains one or more rows of cells. Each cell can be formed into the shape of a Braille character. Braille characters change as the video display changes. Braille and speech are often used together.

    Screen Magnifier

    Does as the name suggests. Standalone applications now being replaced with Orca.

    Orca

    A screen reader for Gnome. Lets users access to information not easily reachable through keyboard navigation commands.

    It defines a set of default behaviours (reaction to application events) and key bindings (reaction to user key presses).

    Gok

    An on-screen keyboard that provides

    • access to the GNOME desktop via dynamically generated keyboards
    • text entry via one of the provided alphanumeric keyboards
    • text entry via a dynamic keyboard created based on the users current system keyboard driver
    • user made keyboardtext entry
    • gui interaction using only switches and/or mouse devices.
    Gestures

    Allow pre-defined mouse movements to run/startup applications. The mouse stroke is associated with a command.

    Emacspeak

    A speech interface that allows visually impaired users to interact independently and efficiently with the computer

    AccessX

    A program the provides various keyboard enhancements, such as StickKeys, MouseKeys, and BounceKeys. Provides two programs:

    • accessx GUI configuration tool. Enables settings on exit. Stores settings in ~/AccessX or somewhere in the users home directory.
    • ax Command-line version of accessx. Also loads the user preferences without opening a terminal. Used to automate startup - add ax to ~/.xsessions file. ~/AccessX file takes the same format as Xresources.

      Sample ~/AccessX configuration entries

       *TimeOutScale.value:                   2
       *StickyKeysToggle.set:                 False
       *MouseKeysToggle.set:                  False
       *ToggleKeysToggle.set:                 False
       *RepeatKeysToggle.set:                 True
       *SlowKeysToggle.set:                   False
       *BounceKeysToggle.set:                 False
       *StickyTwoKeysToggle.set:              True
       *StickyModSoundToggle.set:             True
       *MouseMaxSpeedScale.minimum:           1
       .....
       *KRGDebounceScale.value:               3
      
  • Gnome Accessible Technology (AT) support
    • These notes are based on v2.18 docs.
    • GDM supports "Accessible Login" and AT programs such as GOK (on-screen keyboard) and orca (magnifier and text-to-speech).
    • 'gdmsetup' does not yet work with accessibility -> need to manually edit ascii files

    Autostart configuration

    • /usr/share/gdm/autostart/LoginWindow directory contains files in the format specified by the "FreeDesktop.org Desktop Application Autostart Specification".
    • Any .desktop files in this directory will cause the associated program to automatically start with the login GUI greeter.

    Accessible login

    • best use 'gdmlogin' for both greeters.
    • the GDM greeter programs support the ability to launch AT's at login time via configurable "gestures".
    • these gestures can be defined to be standard keyboard hotkeys, switch device event or mouse motion events.
    • when using the "GTK+ Greeter" the user may also change the visual appearance of the login UI - use a higher-contrast color scheme for better visibility.

    Greeter statements in /etc/gdm/gdm.conf-custom

    [daemon]
    Greeter=/usr/lib/gdmlogin
    RemoteGreeter=/usr/lib/gdmlogin
    

    Configure gestures entries in- /etc/gdm/gdm.conf-custom

    [daemon]
    AllowThemeChange=true                                  # Allow users to change the color and 
                                                           # contrast scheme of the login dialog
    GtkThemesToAllow=HighContrast,HighContrastInverse      # Restrict users to this list of themes
    AddGtkModules=true                                     # Enables use of ATs - Onscreen 
                                                           # Keyboard, Screen Reader or Magnifier
    
    GtkModulesList=gail:atk-bridge:/usr/lib/gtk-2.0/modules/ \
    libkeymouselistener:/usr/lib/gtk-2.0/modules/libdwellmouselistener
    

    Last line causes all GDM GUI programs to be run with the appropriate GTK modules for launching AT programs - allowing user to enable them through the login screen.

    Gesture associations are contained in files AccessKeyMouseEvents and AccessDwellMouseEvents.

    $ ls /etc/gdm/modules
    AccessDwellMouseEvents  AccessKeyMouseEvents  \
    factory-AccessDwellMouseEvents  factory-AccessKeyMouseEvents
    
  • GDM GConf AT keys

    GDM offers GConf keys to control its accessibility features:

    Key Value Description
    /desktop/gnome/interface/accessibility false (boolean) Controls whether the Accessibility infrastructure will be started with the 'gdm'. This is needed for many accessibility technology programs to work.
    /desktop/gnome/applications/at/screen_magnifier_enabled false (boolean) If true starts with 'gdm'.
    /desktop/gnome/applications/at/screen_keyboard_enabled false (boolean) If true enables with 'gdm', enables On-screen keyboard.
    /desktop/gnome/applications/at/screen_reader_enabled false (boolean) If true starts with 'gdm', enables screen reader.
  • Linking GConf Keys to ATs
    • The assistive tool that gets launched depends on the desktop files located in the GDM autostart directory.
    • Any desktop file in the GDM autostart directory can be linked to these GConf keys via specifying that GConf key in the AutostartCondition value in the desktop file.
    • The 'AutostartCondition' line in the desktop file could be one of the following
    AutostartCondition=GNOME /desktop/gnome/applications/at/screen_keyboard_enabled
    AutostartCondition=GNOME /desktop/gnome/applications/at/screen_magnifier_enabled
    AutostartCondition=GNOME /desktop/gnome/applications/at/screen_reader_enabled
    
    • When an accessibility key is true any program which is linked to that key in a GDM autostart desktop file will be launched (unless the Hidden key is set to true in that desktop file).
    • A single GConf key can start multiple assistive tools if there are multiple desktop files with this AutostartCondition in the GDM autostart directory.
  • Change an AT configuration
    example
    The modification

    Replace GOK with the on-screen keyboard application "onboard" and additionally activate the assistive tool "mousetweaks" for dwelling support.

    (1) Create two desktop files, one for onboard and a second for mousetweaks e.g.

    • onboard.desktop and
    • mousetweaks.desktop.

    (2) Place them in the GDM autostart directory (/usr/share/gdm/autostart/LoginWindow).

    Example onboard.desktop

    [Desktop Entry]
    Encoding=UTF-8
    Name=Onboard Onscreen Keyboard
    Comment=Use an on-screen keyboard
    TryExec=onboard
    Exec=onboard --size 500x180 -x 20 -y 10
    Terminal=false
    Type=Application
    StartupNotify=true
    Categories=GNOME;GTK;Accessibility;
    AutostartCondition=GNOME /desktop/gnome/applications/at/screen_keyboard_enabled
    

    Example mousetweaks.desktop

    [Desktop Entry]
    Encoding=UTF-8
    Name=Software Mouse-Clicks
    Comment=Perform clicks by dwelling with the pointer
    TryExec=mousetweaks
    Exec=mousetweaks --enable-dwell -m window -c -x 20 -y 240
    Terminal=false
    Type=Application
    StartupNotify=true
    Categories=GNOME;GTK;Accessibility;
    AutostartCondition=GNOME /desktop/gnome/applications/at/screen_keyboard_enabled
    

    The line with the AutostartCondition links both desktop files to the GConf key for the on-screen keyboard.

    Disable GOK from starting

    Remove or deactivate the desktop file for the GOK on-screen keyboard by either

    • removing the gok.desktop file from the GDM autostart directory or
    • adding the Hidden=true key setting to the gok.desktop file.

    GOK will no longer be started when the user activates the on-screen keyboard in the GDM session, onboard and mousetweaks will be.