Example GTK to create a dock-like bar and strut

dockbar-gtk2.py

#!/usr/bin/env python2
#
# dockbar.py
#
# Example program places a coloured bar across the top of the
# current monitor
#
# demonstrates
#
# (a) creating the bar as an undecorated "dock" window   
# (b) setting its colour
# (c) getting the number of monitors and their sizes
#
#                                                         JL 20140512

import gtk

# Colour style for (b)
colour_rc= """
style "bar-colour" {
    bg[NORMAL] = "Dark Red"
} widget "*bar" style "bar-colour"
"""

#  the size of the bar (its height), in pixels
bar_size = 10

def main ():

    # (a) Create an undecorated dock
    window = gtk.Window()
    window.set_name("bar")
    window.set_type_hint(gtk.gdk.WINDOW_TYPE_HINT_DOCK)
    window.set_decorated(False)
    window.connect("destroy", gtk.main_quit)

    # (b) Style it
    gtk.rc_parse_string(colour_rc)

    # the screen contains all monitors
    screen = window.get_screen()
    width = gtk.gdk.screen_width()
    print "width: %d" % width

    # (c) collect data about each monitor
    monitors = []
    nmons = screen.get_n_monitors()
    print "there are %d monitors" % nmons
    for m in range(nmons):
      mg = screen.get_monitor_geometry(m)
      width = mg.width
      print "monitor %d: %d x %d" % (m,mg.width,mg.height)
      monitors.append(mg)

    # current monitor
    curmon = screen.get_monitor_at_window(screen.get_active_window())
    x, y, width, height = monitors[curmon]
    print "monitor %d: %d x %d (current)" % (curmon,width,height)
    print "bar: start=%d end=%d" % (x,x+width-1)

    # display bar along the top of the current monitor
    window.move(x,y)
    window.resize(width,bar_size)

    # it must be shown before changing properties 
    window.show_all()

    # (d) reserve space (a "strut") for the bar so it does not become obscured
    #     when other windows are maximized, etc
    topw = window.get_toplevel().window
    topw.property_change("_NET_WM_STRUT","CARDINAL",32,gtk.gdk.PROP_MODE_REPLACE,
            [0, 0, bar_size, 0])
    topw.property_change("_NET_WM_STRUT_PARTIAL","CARDINAL",32,gtk.gdk.PROP_MODE_REPLACE,
            [0, 0, bar_size, 0, 0, 0, 0, 0, x, x+width-1, 0, 0])


    # we set _NET_WM_STRUT, the older mechanism as well as _NET_WM_STRUT_PARTIAL
    # but window managers ignore the former if they support the latter.
    #
    # the numbers in the array are as follows:
    #
    # 0, 0, bar_size, 0 are the number of pixels to reserve along each edge of the
    # screen given in the order left, right, top, bottom. Here the size of the bar
    # is reserved at the top of the screen and the other edges are left alone.
    #
    # _NET_WM_STRUT_PARTIAL also supplies a further four pairs, each being a
    # start and end position for the strut (they don't need to occupy the entire
    # edge).
    #
    # In the example, we set the top start to the current monitor's x co-ordinate
    # and the top-end to the same value plus that monitor's width, deducting 1,
    # because the xo-ordinate system starts at 0 rather than 1. The net result
    # is that space is reserved only on the current monitor.
    #
    # co-ordinates are specified relative to the screen (i.e. all monitors together).
    #


    # main event loop
    gtk.main()

if __name__ == "__main__":
    main ()

dockbar-gtk3.py

#!/usr/bin/env python
#
# dockbar.py
#
# Example program places a coloured bar across the top of the
# current monitor
#
# demonstrates
#
# (a) creating the bar as an undecorated "dock" window   
# (b) setting its colour
# (c) getting the number of monitors and their sizes
#
#                                               JL 20140512, 20170220

import gi
gi.require_version('Gtk','3.0')
from gi.repository import Gtk, Gdk
import Xlib
from Xlib.display import Display
from Xlib import X

# Colour style for (b)
stylesheet=b"""
window#bar {
  background-color: darkred;
}
"""

#  the size of the bar (its height), in pixels
bar_size = 10

def main ():

    # Version information
    print("Gtk %d.%d.%d" % (Gtk.get_major_version(),
                            Gtk.get_minor_version(),
                            Gtk.get_micro_version()))

    # (a) Create an undecorated dock
    window = Gtk.Window()
    window.set_name("bar")
    window.set_type_hint(Gdk.WindowTypeHint.DOCK)
    window.set_decorated(False)
    window.connect("delete-event", Gtk.main_quit)

    # (b) Style it
    style_provider = Gtk.CssProvider()
    style_provider.load_from_data(stylesheet)
    Gtk.StyleContext.add_provider_for_screen(
      Gdk.Screen.get_default(),
      style_provider,
      Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION)

    # the screen contains all monitors
    screen = window.get_screen()
    width = screen.width() #width = Gdk.Screen.width()
    print("width: %d" % width)

    # (c) collect data about each monitor
    monitors = []
    nmons = screen.get_display().get_n_monitors()
    print("there are %d monitors" % nmons)
    for m in range(nmons):
      mg = screen.get_monitor_geometry(m)
      print("monitor %d: %d x %d" % (m,mg.width,mg.height))
      monitors.append(mg)

    # current monitor
    curmon = screen.get_monitor_at_window(screen.get_active_window())
    x = monitors[curmon].x
    y = monitors[curmon].y
    width = monitors[curmon].width
    height = monitors[curmon].height
    print("monitor %d: %d x %d (current, offset %d)" % (curmon,width,height,x))
    print("bar: start=%d end=%d" % (x,x+width-1))

    # display bar along the top of the current monitor
    window.move(x,y)
    window.resize(width,bar_size)

    # it must be shown before changing properties 
    window.show_all()

    # (d) reserve space (a "strut") for the bar so it does not become obscured
    #     when other windows are maximized, etc
    # http://stackoverflow.com/questions/33719686  property_change not in gtk3.0
    # https://sourceforge.net/p/python-xlib/mailman/message/27574603
    display = Display()
    topw = display.create_resource_object('window',
                                          window.get_toplevel().get_window().get_xid())

    # http://python-xlib.sourceforge.net/doc/html/python-xlib_21.html#SEC20
    topw.change_property(display.intern_atom('_NET_WM_STRUT'),
                           display.intern_atom('CARDINAL'), 32,
                           [0, 0, bar_size, 0 ],
                           X.PropModeReplace)
    topw.change_property(display.intern_atom('_NET_WM_STRUT_PARTIAL'),
                           display.intern_atom('CARDINAL'), 32,
                           [0, 0, bar_size, 0, 0, 0, 0, 0, x, x+width-1, 0, 0],
                           X.PropModeReplace)


    # we set _NET_WM_STRUT, the older mechanism as well as _NET_WM_STRUT_PARTIAL
    # but window managers ignore the former if they support the latter.
    #
    # the numbers in the array are as follows:
    #
    # 0, 0, bar_size, 0 are the number of pixels to reserve along each edge of the
    # screen given in the order left, right, top, bottom. Here the size of the bar
    # is reserved at the top of the screen and the other edges are left alone.
    #
    # _NET_WM_STRUT_PARTIAL also supplies a further four pairs, each being a
    # start and end position for the strut (they don't need to occupy the entire
    # edge).
    #
    # In the example, we set the top start to the current monitor's x co-ordinate
    # and the top-end to the same value plus that monitor's width, deducting one.
    # because the co-ordinate system starts at zero rather than 1. The net result
    # is that space is reserved only on the current monitor.
    #
    # co-ordinates are specified relative to the screen (i.e. all monitors together).
    #


    # main event loop
    # Gtk.main()
    # Control-C termination broken in GTK3 http://stackoverflow.com/a/33834721
    # https://bugzilla.gnome.org/show_bug.cgi?id=622084
    from gi.repository import GLib
    GLib.MainLoop().run()

if __name__ == "__main__":
    main ()

Thanks! You're an absolute legend!