Getting notified about window title changes

window-managerxorg

…without polling.

I want to detect when the currently focused window changes so that I can update a piece of custom GUI in my system.

Points of interests:

real time notifications. Having 0.2s lag is okay, having 1s lag is meh, having 5s lag is totally unacceptable.
resource friendliness: for this reason, I want to avoid polling. Running xdotool getactivewindow getwindowname every, say, half a second, works quite alright… but is spawning 2 processes a second all that friendly to my system?

In bspwm, one can use bspc subscribe which prints a line with some (very) basic stats, every time window focus changes. This approach seems nice at first, but listening to this won't detect when window title changes by itself (for example, changing tabs in the web browser will go unnoticed this way.)

So, is spawning new process every half a second okay on Linux, and if not, how can I do things better?

One thing that comes to my mind is to try to emulate what window managers do. But can I write hooks for events such as "window creation", "title change request" etc. independently from the working window manager, or do I need to become a window manager itself? Do I need root for this?

(Another thing that came to my mind is to look at xdotool's code and emulate only the things that interest me so that I can avoid all the process spawning boilerplate, but it still would be polling.)

Best Answer

I couldn't get your focus-change approach to work reliably under Kwin 4.x, but modern window managers maintain a _NET_ACTIVE_WINDOW property on the root window that you can listen for changes to.

Here's a Python implementation of just that:

#!/usr/bin/python
from contextlib import contextmanager
import Xlib
import Xlib.display

disp = Xlib.display.Display()
root = disp.screen().root

NET_ACTIVE_WINDOW = disp.intern_atom('_NET_ACTIVE_WINDOW')
NET_WM_NAME = disp.intern_atom('_NET_WM_NAME')  # UTF-8
WM_NAME = disp.intern_atom('WM_NAME')           # Legacy encoding

last_seen = { 'xid': None, 'title': None }

@contextmanager
def window_obj(win_id):
    """Simplify dealing with BadWindow (make it either valid or None)"""
    window_obj = None
    if win_id:
        try:
            window_obj = disp.create_resource_object('window', win_id)
        except Xlib.error.XError:
            pass
    yield window_obj

def get_active_window():
    win_id = root.get_full_property(NET_ACTIVE_WINDOW,
                                       Xlib.X.AnyPropertyType).value[0]

    focus_changed = (win_id != last_seen['xid'])
    if focus_changed:
        with window_obj(last_seen['xid']) as old_win:
            if old_win:
                old_win.change_attributes(event_mask=Xlib.X.NoEventMask)

        last_seen['xid'] = win_id
        with window_obj(win_id) as new_win:
            if new_win:
                new_win.change_attributes(event_mask=Xlib.X.PropertyChangeMask)

    return win_id, focus_changed

def _get_window_name_inner(win_obj):
    """Simplify dealing with _NET_WM_NAME (UTF-8) vs. WM_NAME (legacy)"""
    for atom in (NET_WM_NAME, WM_NAME):
        try:
            window_name = win_obj.get_full_property(atom, 0)
        except UnicodeDecodeError:  # Apparently a Debian distro package bug
            title = "<could not decode characters>"
        else:
            if window_name:
                win_name = window_name.value
                if isinstance(win_name, bytes):
                    # Apparently COMPOUND_TEXT is so arcane that this is how
                    # tools like xprop deal with receiving it these days
                    win_name = win_name.decode('latin1', 'replace')
                return win_name
            else:
                title = "<unnamed window>"

    return "{} (XID: {})".format(title, win_obj.id)

def get_window_name(win_id):
    if not win_id:
        last_seen['title'] = "<no window id>"
        return last_seen['title']

    title_changed = False
    with window_obj(win_id) as wobj:
        if wobj:
            win_title = _get_window_name_inner(wobj)
            title_changed = (win_title != last_seen['title'])
            last_seen['title'] = win_title

    return last_seen['title'], title_changed

def handle_xevent(event):
    if event.type != Xlib.X.PropertyNotify:
        return

    changed = False
    if event.atom == NET_ACTIVE_WINDOW:
        if get_active_window()[1]:
            changed = changed or get_window_name(last_seen['xid'])[1]
    elif event.atom in (NET_WM_NAME, WM_NAME):
        changed = changed or get_window_name(last_seen['xid'])[1]

    if changed:
        handle_change(last_seen)

def handle_change(new_state):
    """Replace this with whatever you want to actually do"""
    print(new_state)

if __name__ == '__main__':
    root.change_attributes(event_mask=Xlib.X.PropertyChangeMask)

    get_window_name(get_active_window()[0])
    handle_change(last_seen)

    while True:  # next_event() sleeps until we get an event
        handle_xevent(disp.next_event())

The more fully-commented version I wrote as an example for someone is in this gist.

UPDATE: Now, it also demonstrates the second half (listening to _NET_WM_NAME) to do exactly what was requested.

UPDATE #2: ...and the third part: Falling back to WM_NAME if something like xterm hasn't set _NET_WM_NAME. (The latter is UTF-8 encoded while the former is supposed to use a legacy character coding called compound text but, since nobody seems to know how to work with it, you get programs throwing whatever stream of bytes they have in there and xprop just assuming it'll be ISO-8859-1.)

Related Solutions

Xorg – How to Invert Colors of the Active Window

If you are looking for a method universal for any window, then this must be made available by the window manager. Therefore I'm afraid any non-composite WM will not be able to do that on demand. So maybe you previously did this with Compiz?

A method of inverting colors regardless of WM is doing this per-application - as with xpdf that you mentioned. There are some applications that have such functionality, but usually you won't be able to invert the colors at run-time. For apps like xpdf, you can either have an alternative desktop menu entry (or icon) that runs the app with special parameters, or define those in your .Xdefaults. For xpdf note also the use of paperColor, foreground and background resources.

Override the window title for an arbitrary window in KDE and set a custom window title

I had this exact same problem.

So I wrote a shell script that I bound to a hotkey.

When I hit the hotkey, it gets the window id of the currently active window (the one that has focus).

Then it gives you a popup dialog where you enter the title you want that window to have.

Then every time that window changes its name, it changes it back to the title you want.

To use the script, you need:

the fish shell
(I wrote it in fish rather than bash cuz bash gives me a headache)
kdialog
some way to bind the script to a hotkey
(I use xbindkeys, cuz all I had to do to get it to work was add:

"[PATH TO SCRIPT]/[NAME OF SCRIPT]" Mod4 + t

(that is, window key + t)
to my /home/o1/.xbindkeysrc)

Thanks to this dude, who gave me the info on the magic xprop stuff.

(Like, a year ago, and then I never got around to writing the script til today. xD )

P.S. If any newbie finds this answer and doesn't know how to use it, just ask me and I'll walk you through it. ^^

EDIT: I updated it so that you can use it from the command line with the switches -t for title_i_want and -w for window_id.

Here's the script:

#!/usr/local/bin/fish

# this block is so you can use it from the command line with -t and -w
if test "$argv" != "" -a (math (count $argv)%2 == 0)
    for i in (seq 1 (count $argv))
        if test $argv[$i] = '-t'
            set title_i_want $argv[(math 1 + $i)]
        else if test $argv[$i] = '-w'
            set window_id $argv[(math 1 + $i)]
        end
    end
    if not test $window_id
        echo "YOU DIDN'T ENTER A `window_id` WITH `-w`,
SO MAKE SURE THE WINDOW YOU WANT HAS FOCUS
TWO SECONDS FROM NOW!"
        sleep 2
    end
end

# get the id of the currently focused window
if not test $window_id
    set window_id (xprop -root _NET_ACTIVE_WINDOW | grep -P -o "0x\w+")
end

# get the title to force on that window

if not test $title_i_want
    set title_i_want (kdialog --title "entitled" --inputbox "type the title you want and hit enter.
to stop renaming,
just enter nothing and hit esc")
end

# this bit is needed for a kludge that allows window renaming
set has_renamed_before "FALSE"
set interrupt_message "WAIT WAIT I WANT A TURN BLOO BLOO BLEE BLUH BLOO" # hopefully i never want to actually use that as a title xD
xprop -f _NET_WM_NAME 8u -set _NET_WM_NAME $interrupt_message -id $window_id

# take the output of xprop
# pipe it into a while loop
# everytime it outputs a new line
# stuff it into a variable named "current_title"
xprop -spy _NET_WM_NAME -id $window_id | while read current_title

    # cut off extraneous not-the-title bits of that string
    set current_title (echo $current_title | grep -P -o '(?<=_NET_WM_NAME\(UTF8_STRING\) = ").*(?="\z)')

    # if the current title is the interrupt message
    # AND
    # this script has renamed the window at least once before
    # then we wanna let the new name take over
    if test $current_title = $interrupt_message -a $has_renamed_before = "TRUE"
        exit
    # if title_i_want is an empty string, exit
    else if test $title_i_want = ""
        xprop -f _NET_WM_NAME 8u -set _NET_WM_NAME "WIDNOW WILL START RENAMING ITSELF AS NORMAL" -id $window_id
        exit
    # otherwise just change the title to what i want
    else if test $current_title != $title_i_want
        xprop -f _NET_WM_NAME 8u -set _NET_WM_NAME "$title_i_want" -id $window_id
        set has_renamed_before "TRUE"
    end
end

EDIT: I actually don't use this Fish script anymore;
I rewrote it in Ruby:

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-

require 'trollop'
opts = Trollop.options do
                        opt :title_i_want,  "title_i_want",     default: ""
                        opt :bluh,          "write to bluh",    default: nil
                        opt :copy_title,    "copy_title",       default: nil
# TODO - AUTO OPTION                                            
                        opt :auto,          "auto",             default: nil
end

title_i_want    = opts[:title_i_want]


def get_current_wid
    `xprop -root _NET_ACTIVE_WINDOW`[/0x\w+/]
end

def with_current_title wid, &block
    IO.popen("xprop -spy _NET_WM_NAME _NET_WM_ICON_NAME -id #{wid}") do |io|
        loop do
            line = io.gets
            exit if line.nil?
            line = line.strip
            # cut off extraneous not-the-title bits of that string
            current_title = line[/(?:_NET_WM_(?:ICON_)?NAME\(UTF8_STRING\) = ")(.*)("$)/, 1]

            block.call current_title unless current_title.nil?
        end
    end
end
def get_current_title wid
    IO.popen("xprop _NET_WM_NAME _NET_WM_ICON_NAME -id #{wid}") do |io|
            line = io.gets.strip
            # cut off extraneous not-the-title bits of that string
            current_title = line[/(?:_NET_WM_(?:ICON_)?NAME\(UTF8_STRING\) = ")(.*)("$)/, 1]

            return current_title unless current_title.nil?
    end
end

if opts[:copy_title]
    # require "muflax"
    p 1
    wid = get_current_wid
    `echo -n '#{get_current_title wid}(WID: #{wid})'|xclip -selection c`
    exit
end
if opts[:bluh]
    require "muflax"
    loop do
        # p 1   #db
        wid = get_current_wid
        # p 2   #db
        File.open "bluh", "a+" do |f| f.puts get_current_title wid end
        while wid == get_current_wid
            # puts "..."    #db
            sleep 1
        end
    end
    exit
end

#> 1A - from terminal - give title_i_want
if not title_i_want.empty?
#> 1A.1 - get current wid - assume it's the terminal_wid
    terminal_wid = get_current_wid
#> 1A.2 - wait for wid to change
    while get_current_wid == terminal_wid
        puts "focus the window you want to title «#{title_i_want}»..."
        sleep 1
    end
#> 1A.3 - set new wid to target TWID
    TWID = get_current_wid

#> 1B - from hotkey (or just sleeping) - no give title_i_want
else
#> 1B.1 - set current wid to target TWID
    TWID = get_current_wid
#> 1B.2 - get title_i_want (with kdialog)
#> 1B.2.1 - default to current title
    with_current_title TWID do |current_title|
        # v :current_title  #db
        default_title = current_title

        sublime_match = /
            (?<beginning>.*?)                                   # beginning might be...
                                                                #           path
                                                                #           untitled, find results, other useless junk
                                                                #           ? dired
            (?<dirty>\s•)?                                      # dirty?
            (?:\s\(\.?(?<projname>[^()]*)\))?                   # project name, preceded by "." (i name them that way), and in rkaks (sublime does that)
                                                                # or, sans dot, it's the dir, if the window was opened as a dir
            (?<issub>\s-\sSublime\sText\s2\s\(UNREGISTERED\))   # garbage at the end that marks it as a sublime window
        /x =~ current_title

        #if it's a sublime window...
        if sublime_match
            dummy = beginning.split("/")
            if dummy.length > 1
                taildir = dummy[-2]
            end
            /? (?<direddir>.*)/ =~ beginning

            default_title =
            if      projname    ;   projname
            elsif   taildir     ;   taildir
            elsif   direddir    ;   direddir
            else                ;   beginning
            end
        end

        if opts[:auto]
            title_i_want = default_title
        else
            title_i_want = `kdialog --title "entitled" --inputbox "type the title you want and hit enter.\nto stop renaming,\njust enter nothing and hit esc" '#{default_title}'`.chomp
        end
        break
    end
end


# v :terminal_wid   #db
# v :TWID           #db
# v :ARGV           #db
# v :title_i_want   #db


def set_title wid, title
    `xprop  -f _NET_WM_NAME 8u      -set _NET_WM_NAME       "#{title}"  -id #{wid}`
    `xprop  -f _NET_WM_ICON_NAME 8u -set _NET_WM_ICON_NAME  "#{title}"  -id #{wid}`
end


#> 2 - apply title to TWID
#> 2.1 - allow de-naming
#> 2.2 - allow renaming

# this bit is needed for a kludge that allows window renaming
has_renamed_before  = false
interrupt_message   = "WAIT WAIT I WANT A TURN BLOO BLOO BLEE BLUH BLOO" # hopefully i never want to actually use that as a title xD
`xprop -f _NET_WM_NAME 8u -set _NET_WM_NAME '#{interrupt_message}' -id #{TWID}`

with_current_title TWID do |current_title|

    # if title_i_want is an empty string, exit
    if title_i_want.empty?
        # p 1   #db
        set_title TWID, "WINDOW WILL START RENAMING ITSELF AS NORMAL"
        exit

    # if the current title is the interrupt message
    # AND
    # this script has renamed the window at least once before
    # then we wanna let the new name take over
    elsif current_title == interrupt_message and has_renamed_before
        # p 2   #db
        exit


    # otherwise just change the title to what i want
    elsif current_title != title_i_want
        # p 3   #db
        set_title TWID, title_i_want
        has_renamed_before = true
    end
end

Best Answer

Related Solutions

Xorg – How to Invert Colors of the Active Window

Override the window title for an arbitrary window in KDE and set a custom window title

Related Question