backends/x11: Handle a11y changing XKB events together with other XKB events

There's no need for an XEvent filter, since this is already code close enough
to MetaBackendX11 XEvent handling and always required anyways. Make the a11y
configuration checks happen directly from MetaBackendX11 event handling.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3153>

src/backends/x11/meta-backend-x11.c

@@ -346,6 +346,8 @@ handle_host_xevent (MetaBackend *backend,
 {
   MetaBackendX11 *x11 = META_BACKEND_X11 (backend);
   MetaBackendX11Private *priv = meta_backend_x11_get_instance_private (x11);
+  ClutterBackend *clutter_backend = meta_backend_get_clutter_backend (backend);
+  ClutterSeat *seat = clutter_backend_get_default_seat (clutter_backend);
   MetaContext *context = meta_backend_get_context (backend);
   gboolean bypass_clutter = FALSE;
   MetaDisplay *display;
@@ -408,6 +410,17 @@ handle_host_xevent (MetaBackend *backend,
                                                                      layout_group);
                 }
               break;
+            case XkbControlsNotify:
+              /* 'event_type' is set to zero on notifying us of updates in
+               * response to client requests (including our own) and non-zero
+               * to notify us of key/mouse events causing changes (like
+               * pressing shift 5 times to enable sticky keys).
+               *
+               * We only want to update our settings when it's in response to an
+               * explicit user input event, so require a non-zero event_type.
+               */
+              if (xkb_ev->ctrls.event_type != 0)
+                meta_seat_x11_check_xkb_a11y_settings_changed (seat);
             default:
               break;
             }

src/backends/x11/meta-xkb-a11y-x11.c

@@ -43,8 +43,6 @@
                                       XkbAccessXFeedbackMask  | \
                                       XkbControlsEnabledMask
 
-static int _xkb_event_base;
-
 static Display *
 xdisplay_from_seat (ClutterSeat *seat)
 {
@@ -86,8 +84,8 @@ set_xkb_desc_rec (Display    *xdisplay,
   meta_clutter_x11_untrap_x_errors ();
 }
 
-static void
+void
-check_settings_changed (ClutterSeat *seat)
+meta_seat_x11_check_xkb_a11y_settings_changed (ClutterSeat *seat)
 {
   MetaSeatX11 *seat_x11 = META_SEAT_X11 (seat);
   MetaBackend *backend = meta_seat_x11_get_backend (META_SEAT_X11 (seat_x11));
@@ -145,37 +143,11 @@ check_settings_changed (ClutterSeat *seat)
   XkbFreeKeyboard (desc, XkbAllComponentsMask, TRUE);
 }
 
-static MetaX11FilterReturn
-xkb_a11y_event_filter (XEvent       *xevent,
-                       ClutterEvent *clutter_event,
-                       gpointer      data)
-{
-  ClutterSeat *seat = CLUTTER_SEAT (data);
-  XkbEvent *xkbev = (XkbEvent *) xevent;
-
-  /* 'event_type' is set to zero on notifying us of updates in
-   * response to client requests (including our own) and non-zero
-   * to notify us of key/mouse events causing changes (like
-   * pressing shift 5 times to enable sticky keys).
-   *
-   * We only want to update out settings when it's in response to an
-   * explicit user input event, so require a non-zero event_type.
-   */
-  if (xevent->xany.type == (_xkb_event_base + XkbEventCode) &&
-      xkbev->any.xkb_type == XkbControlsNotify && xkbev->ctrls.event_type != 0)
-    check_settings_changed (seat);
-
-  return META_X11_FILTER_CONTINUE;
-}
-
 static gboolean
 is_xkb_available (Display *xdisplay)
 {
   int opcode, error_base, event_base, major, minor;
 
-  if (_xkb_event_base)
-    return TRUE;
-
   if (!XkbQueryExtension (xdisplay,
                           &opcode,
                           &event_base,
@@ -187,8 +159,6 @@ is_xkb_available (Display *xdisplay)
   if (!XkbUseExtension (xdisplay, &major, &minor))
     return FALSE;
 
-  _xkb_event_base = event_base;
-
   return TRUE;
 }
 
@@ -337,11 +307,6 @@ meta_seat_x11_apply_kbd_a11y_settings (ClutterSeat         *seat,
 gboolean
 meta_seat_x11_a11y_init (ClutterSeat *seat)
 {
-  MetaSeatX11 *seat_x11 = META_SEAT_X11 (seat);
-  MetaBackend *backend = meta_seat_x11_get_backend (META_SEAT_X11 (seat_x11));
-  ClutterBackend *clutter_backend = meta_backend_get_clutter_backend (backend);
-  MetaClutterBackendX11 *clutter_backend_x11 =
-    META_CLUTTER_BACKEND_X11 (clutter_backend);
   Display *xdisplay = xdisplay_from_seat (seat);
   guint event_mask;
 
@@ -352,9 +317,5 @@ meta_seat_x11_a11y_init (ClutterSeat *seat)
 
   XkbSelectEvents (xdisplay, XkbUseCoreKbd, event_mask, event_mask);
 
-  meta_clutter_backend_x11_add_filter (clutter_backend_x11,
-                                       xkb_a11y_event_filter,
-                                       seat);
-
   return TRUE;
 }

src/backends/x11/meta-xkb-a11y-x11.h

@@ -34,3 +34,5 @@ meta_seat_x11_apply_kbd_a11y_settings (ClutterSeat         *seat,
 
 gboolean
 meta_seat_x11_a11y_init               (ClutterSeat            *seat);
+
+void meta_seat_x11_check_xkb_a11y_settings_changed (ClutterSeat *seat);