How do I get the active window on Gnome Wayland?

Question

Background: I'm working on a piece of software called ActivityWatch that logs what you do on your computer. Basically an attempt at addressing some of the issues with: RescueTime, selfspy, arbtt, etc.

One of the core things we do is log information about the active window (class and title). In the past, this has been done using on Linux using xprop and now python-xlib without issue.

But now we have a problem: Wayland is on the rise, and as far as I can see Wayland has no notion of an active window. So my fear is that we will have to implement support for each and every desktop environment available for Wayland (assuming they'll provide the capability to get information about the active window at all).

Hopefully they'll eventually converge and have some common interface to get this done, but I'm not holding my breath...

I've been anticipating this issue. But today we got our first user request for Wayland support by an actual Wayland user. As larger distros are adopting Wayland as the default display server protocol (Fedora 25 is already using it, Ubuntu will switch in 17.10 which is coming soon) the situation is going to get more critical over time.

Relevant issues for ActivityWatch:

• https://github.com/ActivityWatch/aw-watcher-window/issues/18
• https://github.com/ActivityWatch/activitywatch/issues/92

There are other applications like ActivityWatch that would require the same functionality (RescueTime, arbtt, selfspy, etc.), they don't seem to support Wayland right now and I can't find any details about them planning to do so.

I'm now interested in implementing support for Gnome to start off with and follow up with others as the path becomes more clear.

A similar question concerning Weston has been asked here: get the list of active windows in wayland weston

Edit: I asked in #wayland on Freenode, got the following reply:

15:20:44  ErikBjare    Hello everybody. I'm working on a piece of self-tracking software called ActivityWatch (https://github.com/ActivityWatch/activitywatch). I know this isn't exactly the right place to ask, but I was wondering if anyone knew anything about getting the active window in any Wayland-using DE.
15:20:57  ErikBjare    Created a question on SO: https://stackoverflow.com/questions/45465016/how-do-i-get-the-active-window-on-gnome-wayland
15:21:25  ErikBjare    Here's the issue in my repo for it: https://github.com/ActivityWatch/activitywatch/issues/92
15:22:54  ErikBjare    There are a bunch of other applications that depend on it (RescueTime, selfspy, arbtt, ulogme, etc.) so they'd need it as well
15:24:23  blocage      ErikBjare, in the core protocol you cannot know which windnow has the keyboard or cursor focus
15:24:39  blocage      ErikBjare, in the wayland core protocol *
15:25:10  blocage      ErikBjare, you can just know if your window has the focus or not, it a design choise
15:25:23  blocage      avoid client spying each other
15:25:25  ErikBjare    blocage: I'm aware, that's my reason for concern. I'm not saying it should be included or anything, but as it looks now every DE would need to implement it themselves if these kind of applications are to be supported
15:25:46  ErikBjare    So wondering if anyone knew the teams working with Wayland on Gnome for example
15:26:11  ErikBjare    But thanks for confirming
15:26:29  blocage      ErikBjare, DE should create a custom extension, or use D-bus or other IPC
15:27:31  blocage      ErikBjare, I guess some compositor are around here, but I do not know myself if there is such extension already
15:27:44  blocage      compositor developers *
15:28:36  ErikBjare    I don't think there is (I've done quite a bit of searching), so I guess I need to catch the attention of some DE developers
15:29:16  ErikBjare    Thanks a lot though
15:29:42  ErikBjare    blocage: Would you mind if I shared logs of our conversation in the issue?                                     
15:30:05  blocage      just use it :) it's public                                                                                               
15:30:19  ErikBjare    ty :)

Edit 2: Filed an enhancement issue in the Gnome bugtracker.

tl;dr: How do I get the active window on Gnome when using Wayland?

Answer 1

In my opinion the best choise you have is not Wayland or any available library (there are not one). Actually who know in gnome-wayland about the active windows is Mutter, so you need to find a way to ask to Mutter the active windows. Gnome can develp an API to internally ask to mutter the active window and restore the funcionality. But really, you have not a place to ask for it. Mutter will not develop an API to access to his internal representation, becasue this will be pretty specific of Mutter only and not to all Wayland windows manager. So this need to be added to an external library, where this library could talk probably with the current window manager that it's in use to resolve your request in a general way.

Another posibility is add a Wayland plugin where all windows manager will have a way to share the current active windows and in some way a library to talk directly with wayland to restore the funcionality.

So, your app is in a big problem. Most you can do is request this on mutter (where is know the active windows), but in my opinion it can not be resolved in Mutter.

I hope this will help you and you can find a way. Good loock.

Answer 2

I have a script called preguiça.py, that does exactly what you're doing, though it is probably a lot simpler and I haven't released it.

For my script, I acquired the window title using PyGObject's Window Navigator Construction Kit (Wnck).

Here's a simplified version of it, with the essencial parts:

from gi.repository import Wnck
from gi.repository import GObject

def changed (screen, window, data):
    print ("Changed!")
#    window = screen.get_active_window()
    if window:
        print ("Title: %s" % window.get_name())

screen = Wnck.Screen.get_default ()
screen.connect ("active-window-changed", changed, None)

mainLoop = GObject.MainLoop ()

try:
    mainLoop.run ()
except KeyboardInterrupt:
    print ("Hey")

mainLoop.unref ()

The actual code for what you're asking is actually commented out on the example above (I didn't need to capture the window, as the callback already receives it), but you may need it depending on your implementation.

I wrote it for X, and it didn't complain when I switched to Wayland, so it should probably work for you.

Note it doesn't get the information from Wayland, as you asked, but it is probably actually better, as it will be X/Wayland-agnostic. It got the title from an xterm I opened, so it should be toolkit-agnostic, as well.

Don't ask me on the details of the implementation, though. The code is at least four years old :)