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Contents
  1. 1. Summary
  2. 2. gnome-screensaver
  3. 3. xscreensaver
  4. 4. xset
  5. 5. Screensaver extension
  6. 6. Reference

This document describes the screensaver work flow.

Summary

Usually there are 2 stages for the process of screen saver.

  • stage 1: the application to call the screensaver daemon to show the screensaver, such as a picture.
  • stege 2: to shutdown the monitor, which will call the DDX from X server.

Below are screensaver applications:

  • gnome-screensaver
  • xscreensaver
    Both of them will NOT call DDX driver xf86IsUnblank() as DDX Design.
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    Returns TRUE when the screen saver mode specified by mode requires the screen be unblanked, and FALSE otherwise. The screen saver modes that require blanking are SCREEN_SAVER_ON and SCREEN_SAVER_CYCLE, and the screen saver modes that require unblanking are SCREEN_SAVER_OFF and SCREEN_SAVER_FORCER. Drivers may call this helper from their SaveScreen() function to interpret the screen saver modes.

Helper command:

  • xset
    DDX driver will be called.

There is a screen saver extension in X server.

  • Currently I didn’t find it is enabled during the work.
  • If it works, the *(pScreen->screensaver.ExternalScreenSaver) will be called during dixSaveScreens().

Anyway, whether screen saver extension enabled or not, the related setting will be done in dixSaveScreens()
to check the type is SCREEN_SAVER_ON, SCREEN_SAVER_OFF or others.

  • xset will go through this path.
  • xscreensaver will only show the screensaver as application.

gnome-screensaver

It’s default screensaver in Ubuntu system.

  • The daemon will start as root when system boot

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    root      2095  0.0  1.2 562416 42520 ?        Sl   04:20   0:01 /usr/bin/gnome-screensaver --no-daemon

  • gnome-screensaver command to show blank screen by default

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    Usage:
    gnome-screensaver-command [OPTION...]

    Help Options:
    -h, --help           Show help options

    Application Options:
    --exit               Causes the screensaver to exit gracefully
    -q, --query          Query the state of the screensaver
    -t, --time           Query the length of time the screensaver has been active
    -l, --lock           Tells the running screensaver process to lock the screen immediately
    -a, --activate       Turn the screensaver on (blank the screen)
    -d, --deactivate     If the screensaver is active then deactivate it (un-blank the screen)
    -V, --version        Version of this application

xscreensaver

If you like, you can install xscreensaver, co-existing with the gnome-screensaver, or remove it.

  • xscreensaver will call libGL.so to show the screensaver.

    • If loading libGL.so is failed, no screensaver will be shown.

  • Install xscreensaver

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    $ sudo apt-get install xscreensaver

    Optional:
    $ sudo apt-get install xscreensaver-data-extra xscreensaver-gl-extra

  • Start xscreensaver daemon as non-root

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    $ xscreensaver -nosplash &

  • start configuration GUI and start daemon automatically.

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    $ xscreensaver-demo

  • xscreensaver command to show the screensaver with random picture by default

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    usage: xscreensaver-command -<option>

    This program provides external control of a running xscreensaver process.
    Version 5.15, copyright (c) 1991-2008 Jamie Zawinski <jwz@jwz.org>.

    The xscreensaver program is a daemon that runs in the background.
    You control a running xscreensaver process by sending it messages
    with this program, xscreensaver-command.  See the man pages for
    details.  These are the arguments understood by xscreensaver-command:

    -activate     Turn on the screensaver (blank the screen), as if the user
                  had been idle for long enough.

    -deactivate   Turns off the screensaver (un-blank the screen), as if user
                  activity had been detected.

xset

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usage:  xset [-display host:dpy] option ...

To control Energy Star (DPMS) features:
  -dpms      Energy Star features off
  +dpms      Energy Star features on
   dpms [standby [suspend [off]]]
        force standby 
        force suspend 
        force off 
        force on 
        (also implicitly enables DPMS features) 
        a timeout value of zero disables the mode 
For screen-saver control:
  s [timeout [cycle]]  s default    s on
  s blank              s noblank    s off
  s expose             s noexpose
  s activate           s reset
For status information:  q

  • xset s activate

    • Turn off the monitor
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      dix_main
        Dispatch
          dixSaveScreens
            AMDGPUSaveScreen_KMS
              xf86IsUnblank
                crtc->funcs->dpms
                output->funcs->dpms

  • xset s reset

    • Recovery the monitor

  • xset dpms force off

    • Turn off the monitor, wait for keyboard or mouse to activate
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      dix_main
        Dispatch
          ProcDPMSForceLevel
            DPMSSet
              dixSaveScreens
                AMDGPUSaveScreen_KMS
                  xf86IsUnblank
                    crtc->funcs->dpms
                    output->funcs->dpms

Screensaver extension

X server has a extension for screensaver.

  • The initial function ScreenSaverExtensionInit() in Xext/saver.c
  • By default it looks no screensaver extension in X server.
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    CreateRootWindow(ScreenPtr pScreen)
    {
    ...
    pScreen->screensaver.ExternalScreenSaver = NULL;
    ...
    }

Reference

Contents
  1. 1. Summary
  2. 2. gnome-screensaver
  3. 3. xscreensaver
  4. 4. xset
  5. 5. Screensaver extension
  6. 6. Reference