Ubuntu Wiki

xscreensaver

Detect

• Use $DISPLAY and search to find a window with the unique XA_SCREENSAVER_VERSION property.

• xscreensaver-demo (the control panel) is driver/demo-Gtk.c and uses:

  xscreensaver_running_p (state *s)
  {
    char *rversion = NULL;
    server_xscreensaver_version (dpy, &rversion, 0, 0);
    return rversion != NULL;
  }

• To do it from the command line:

  $ xscreensaver-command -version
  xscreensaver-command: no screensaver is running on display :0.0

Communicate

• Uses $DISPLAY and then send a custom XAtom via an Xevent:

  $ xscreensaver-command -deactive
  
  XA_DEACTIVATE = XInternAtom (dpy, "DEACTIVATE", False);
  if (!strncmp (s, "-deactivate", L)) cmd = &XA_DEACTIVATE;
  event.xclient.message_type = XA_SCREENSAVER;
  event.xclient.data.l[0] = (long) command;

Notes

• after matching, xscreensaver-4.23/driver/screensaver-command.c which calls into remote.c for the dirty work.

gnome-screensaver

• gnome-screensaver-2.13.92/src/gnome-screensaver-command.c:

Detect

• Use the Session DBus to check for org.gnome.ScreenSaver being owned:

  connection = dbus_bus_get (DBUS_BUS_SESSION, &dbus_error);
  dbus_bus_name_has_owner(connection, "org.gnome.ScreenSaver");

• On the command-line:

  $ gnome-screensaver-command --version
  gnome-screensaver-command 2.14.0

Communicate

• Sends a Message over the session DBus:

  message = dbus_message_new_method_call(
    "org.gnome.ScreenSaver",
    "/org/gnome/ScreenSaver",
    "org.gnome.ScreenSaver",
    "Poke");
  message = dbus_message_new_method_call(
    "org.gnome.ScreenSaver",
    "/org/gnome/ScreenSaver",
    "org.gnome.ScreenSaver",
    ("setActive", FALSE));

• Or on the command-line:

  $ gnome-screensaver --poke
  $ gnome-screensaver --deactivate

  ...which basically end up doing the same thing after 4 levels of indirection as Poke calls gs_watcher_reset() which calls:

  gs_watcher_set_active (watcher, FALSE);
  gs_watcher_set_active (watcher, TRUE);

Kscreensaver

• Kscreensaver already has code to (a) detect (b) ping xscreensaver and kscreensaver: http://www.koders.com/cpp/fid5EFB9027E1545F96F8B3A51780B37B88AB255A0D.aspx