command: add read-only focused property

Add a property that returns whether the window is focused, currently
only for X11 and Wayland.

My use cause for this is having an equivalent of pause-when-minimize.lua
for tiling window managers: make mpv play only while it's in the current
workspace or is focused (I'm fine with either one but prefer focus).
On X I do this by observing display-names, which is empty when the
rectangles of the display and mpv don't intersect, but on Wayland its
value doesn't change when mpv leaves the current workspace (and the same
check doesn't work since the geometries still intersect).

This could later be made writable as requested in #6252.

Note that on Wayland se shouldn't consider an unactivated window with
keyboard input focused.

The wlroots compositors I tested set activated after changing the
keyboard focus, so if you set wl->focused only in
keyboard_handle_enter() and keyboard_handle_leave() to avoid adding the
"has_keyboard_input" member, focused isn't set to true when first
opening mpv until you focus another window and focus mpv again.

Conversely, if that order can't be assumed for all compositors, we
should toggle wl->focused when necessary in keyboard_handle_enter() and
keyboard_handle_leave() as well as in handle_toplevel_config().

1 files changed, 3 insertions, 0 deletions

diff --git a/DOCS/man/input.rst b/DOCS/man/input.rst
index 739f5f1022..18027ce17a 100644
--- a/DOCS/man/input.rst
+++ b/DOCS/man/input.rst
@@ -2439,6 +2439,9 @@ Property list
     since setting the option, and the window size was not restricted in other
     ways. The property is unavailable if no video is active.
 
+``focused``
+    Whether the window has focus. Currently works only on X11 and Wayland.
+
 ``display-names``
     Names of the displays that the mpv window covers. On X11, these
     are the xrandr names (LVDS1, HDMI1, DP1, VGA1, etc.). On Windows, these