How to know which window has focus and how to change it?

Question

I would like to know how can I ask X11 which windows has focus. And if for any reason my own application (that may be visible or not) got the focus I want be able to let the

Answer 1

Use this XQueryTree to find the currently active, or top-most window.

Here is a function, when given a display, it will find the current window in focus:

static Window
GetCurrWindow(d)
Display *d;
{
Window foo;
Window win;
int bar;

    do{
    (void) XQueryPointer(d, DefaultRootWindow(d), &foo, &win,
        &bar, &bar, &bar, &bar, &bar);
    } while(win <= 0);


#ifdef VROOT
    {
    int n;
    Window *wins;
    XWindowAttributes xwa;

    (void) fputs("=xwa=", stdout);

    /* do{  */
        XQueryTree(d, win, &foo, &foo, &wins, &n);
    /* } while(wins <= 0); */
    bar=0;
    while(--n >= 0) {
        XGetWindowAttributes(d, wins[n], &xwa);
        if( (xwa.width * xwa.height) > bar) {
        win = wins[n];
        bar = xwa.width * xwa.height;
        }
        n--;
    }
    XFree(wins);
    }
#endif
    return(win);
}

http://tronche.com/gui/x/xlib/window-information/XQueryTree.html

I found the source:

http://examples.oreilly.com/networksa/tools/xsnoop.c

Good Luck

Answer 2

I recommend an application called XDoTool. It supports quite a lot of queries, controls, and even hooks.

> xdotool getwindowfocus               # 29360135
> xdotool getwindowfocus getwindowpid  # 12988
> xdotool getwindowfocus getwindowname # tilda
> xdotool getwindowfocus behave '%@' blur getmouselocation
#      or focus, mouse-enter, etc.
x:514 y:317 screen:0 window:56623121
x:271 y:26 screen:0 window:56623121
...

Commands like behave accept a callback, which can be built-in like getmouselocation or external like exec notify-send 'focused window', exec zsh myscript.zsh, etc., however you want to use it.

Edit - you can focus using xdotool windowfocus [options] [window], as in xdotool search --class firefox windowfocus. In my case this causes errors because Firefox shows up as a couple dozen 'windows', but all have the same PID; it works given the right ID. Hopefully that's a start.

Edit 2 - the 'window ID' is the decimal representation of the window pointer, e.g. from xprop:

> xprop -root _NET_ACTIVE_WINDOW
_NET_ACTIVE_WINDOW(WINDOW): window id # 0x1c00007, 0x0
> xdotool getwindowfocus
29360135
> printf '%d\n' '0x1c00007'
29360135

Answer 3

You probably want the XGetInputFocus call.

Window focused;
int revert_to;

XGetInputFocus(dpy, &focused, &revert_to);

In this snippet, focused will be the window with current input focus, getting keyboard events and mouse button presses.

This will work even if the window manager does not set the _NET_ACTIVE_WINDOW property on the root window, as specified by EWMH. A few window managers, such as dwm and my 9wm, don't set this.

Answer 4

Take a look at the _NET_ACTIVE_WINDOW value of the root window which is set by most modern window managers:

xprop -root _NET_ACTIVE_WINDOW

This value can, of course, be obtained using Xlib library calls.