How do I get a list of all windows on my gnome2 desktop using pygtk?

Question

I'm a bit confused with some gtk and gnome concepts. I'm trying to get list of non minimized windows on my gnome2 desktop, but after reading the pygtk documentation and inspecting the results, I can't understand the results.

Neither of the two snippets below appears to work.

First I tried this..

>>> gtk.gdk.window_get_toplevels()
[<gtk.gdk.Window object at 0xb74339b4 (GdkWindow at 0x8a4c170)>]

>>> gtk.gdk.window_get_toplevels()[0].get_children()
[]

then this

>>> d = gtk.gdk.DisplayManager()   
>>> d.get_default_display().get_screen(0).get_root_window().get_children() 
[<gtk.gdk.Window object at 0x89dcc84 (GdkWindow at 0x8a4c170)>, <gtk.gdk.Window object at 0x89dccac (GdkWindow at 0x8a4c0c0)>] 

As seen in the console output, the second option returns two windows. But I haven't been able to figure out what they are. None of them has any children and I allways get those two windows regardless how many windows I have on my desktop.

Could anybody explain the hierarchy of objects of the typical gtk based desktop environment? I can't understand why the above code doesn't work.

Please refrain from posting alternative solutions that resource to wnck, xlib, qt, etc. I'm more interested in understanding what I am doing wrong than in getting advice such us checking other libraries.

Answer 1

Your constraint is like saying "I want to build a CD player using only a banana. Please refrain from posting alternative solutions that resort to lasers." GTK can't do that, you're using the wrong tool for the job.

Here's an explanation of what a "window" actually means and why your code doesn't work:

First off, you need to understand the difference between a gtk.Window and a gtk.gdk.Window. A GTK window is a top level GTK widget that can contain other widgets. It is usually linked to a window on your desktop, but doesn't have to be - in GTK 3 there is an OffscreenWindow.

A GDK window, on the other hand, is platform-dependent. On an X desktop it is a thin wrapper around an X window, which is not necessarily a toplevel desktop window. On other systems it exists to abstract away the windowing system. A GDK window receives events, so some GTK non-window widgets have their own GDK windows. "Window" is really a terrible name for these objects, but it was inherited from X and it's probably not going to change.

Each GTK process only knows about its own windows. You can get a list of the toplevel GTK windows of your own application using gtk.window_list_toplevels(). Getting the children of these windows should return you the GTK widgets that they contain. However, you can't descend into the widget hierarchy of other processes' windows. For example, what if another process has a window with a child widget that is a custom widget that your process doesn't know about? What should it report as the type of that widget?

Getting a list of the toplevel GDK windows with gtk.gdk.window_get_toplevels() is basically the same as getting a list of the toplevel X windows, as far as I understand it. You have no way of knowing what kind of windows they are - they might be the Gnome Panel, or they might be Qt windows, or they might be something else altogether that doesn't correspond with a desktop window.

Libwnck (link to the overview of what it does) can get you a list of non-minimized windows, and their titles, but it won't allow you to see inside them. There's no way to do that. Libwnck uses GDK internally, so technically you could do it using GDK, but why would you bother if there's already a library that does that for you? If you really want to do it yourself, look at the libwnck source code.

Answer 2

The windows you get are the windows that were created within your process. To get the list of windows, you need to query the properties of the root window, like this:

import gtk.gdk
root = gtk.gdk.get_default_root_window()
for id in root.property_get('_NET_CLIENT_LIST')[2]:
    w = gtk.gdk.window_foreign_new(id)
    if w:
        print(w.property_get('WM_NAME')[2])

Please note that GDK is a thin layer over underlying OS graphics engine (X11/Quartz/Aqua/GDI etc) and result may differ on different NIX devices.