input-relay: Add mute key as volume key

Add KEY_MUTE as volume key. It will be mapped to KEY_MACRO28 and
use wpctl to toggle the mute of the default audio sink. The toggle of
the mute state will be done once when the key is pressed instead of
continuously toggling it when it is held down.
This allows the mute button on keyboards to work properly.

Signed-off-by: SuperTuxii <123881249+SuperTuxii@users.noreply.github.com>

input/input-relay.py

@@ -132,10 +132,10 @@ KEY_A = 30
 REL_X, REL_Y, REL_WHEEL, REL_MAX = 0x00, 0x01, 0x08, 0x0F
 BTN_LEFT, BTN_RIGHT, BTN_MIDDLE, BTN_SIDE, BTN_EXTRA = 0x110, 0x111, 0x112, 0x113, 0x114
 KEY_LEFTMETA, KEY_RIGHTMETA = 125, 126
-KEY_VOLUMEDOWN, KEY_VOLUMEUP = 114, 115
-# Volume keys are remapped to KEY_MACRO29 and KEY_MACRO30: above 255, so X11 can't
-# carry them, and bound to nothing in the default keymap.
-VOLUME_STANDIN = {KEY_VOLUMEUP: 0x2AC, KEY_VOLUMEDOWN: 0x2AD}
+KEY_MUTE, KEY_VOLUMEDOWN, KEY_VOLUMEUP = 113, 114, 115
+# Volume keys are remapped to KEY_MACRO28, KEY_MACRO29 and KEY_MACRO30: above 255, so X11
+# can't carry them, and bound to nothing in the default keymap.
+VOLUME_STANDIN = {KEY_MUTE: 0x2AB, KEY_VOLUMEUP: 0x2AC, KEY_VOLUMEDOWN: 0x2AD}
 VOLUME_ORIGINAL = {v: k for k, v in VOLUME_STANDIN.items()}
 VOLUME_CODES = set(VOLUME_STANDIN) | set(VOLUME_ORIGINAL)
 BUS_USB, BUS_BLUETOOTH, BUS_VIRTUAL = 0x03, 0x05, 0x06
@@ -383,6 +383,10 @@ class Volume:
 
     def key(self, fd, code, value, now):
         if value == 1:
+            if VOLUME_ORIGINAL.get(code, code) == KEY_MUTE:
+                subprocess.Popen(["wpctl", "set-mute", "@DEFAULT_AUDIO_SINK@", "toggle"],
+                                stdin=subprocess.DEVNULL, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+            else:
                 self.held = (fd, code)
                 self.step(code)
                 self.next_at = now + self.DELAY