wayland/pointer: Set focus to NULL when the cursor is hidden

This is important when using a touchscreen or stylus instead of a mouse
or touchpad. If the cursor only gets hidden and the focus stays the
same, the window will still send hover events to the UI element under
the cursor causing unexpected distractions while interacting with the
touchscreen.

Fix this by emitting a visibility-changed signal from the cursor tracker
which then triggers a focus surface sync and always set the focus
surface to NULL when it's synced while the cursor is hidden.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/448

src/backends/meta-cursor-tracker.c

@@ -50,6 +50,7 @@ enum
 {
   CURSOR_CHANGED,
   CURSOR_MOVED,
+  VISIBILITY_CHANGED,
   LAST_SIGNAL
 };
 
@@ -173,6 +174,13 @@ meta_cursor_tracker_class_init (MetaCursorTrackerClass *klass)
                                         G_TYPE_NONE, 2,
                                         G_TYPE_FLOAT,
                                         G_TYPE_FLOAT);
+
+  signals[VISIBILITY_CHANGED] = g_signal_new ("visibility-changed",
+                                              G_TYPE_FROM_CLASS (klass),
+                                              G_SIGNAL_RUN_LAST,
+                                              0, NULL, NULL,
+                                              g_cclosure_marshal_VOID__VOID,
+                                              G_TYPE_NONE, 0);
 }
 
 /**
@@ -433,6 +441,8 @@ meta_cursor_tracker_set_pointer_visible (MetaCursorTracker *tracker,
   tracker->is_showing = visible;
 
   sync_cursor (tracker);
+
+  g_signal_emit (tracker, signals[VISIBILITY_CHANGED], 0);
 }
 
 MetaCursorSprite *

src/wayland/meta-wayland-pointer.c

@@ -226,6 +226,14 @@ static void
 sync_focus_surface (MetaWaylandPointer *pointer)
 {
   MetaDisplay *display = meta_get_display ();
+  MetaBackend *backend = meta_get_backend ();
+  MetaCursorTracker *cursor_tracker = meta_backend_get_cursor_tracker (backend);
+
+  if (!meta_cursor_tracker_get_pointer_visible (cursor_tracker))
+    {
+      meta_wayland_pointer_set_focus (pointer, NULL);
+      return;
+    }
 
   switch (display->event_route)
     {
@@ -473,6 +481,13 @@ meta_wayland_pointer_on_cursor_changed (MetaCursorTracker *cursor_tracker,
     meta_wayland_surface_update_outputs (pointer->cursor_surface);
 }
 
+static void
+meta_wayland_pointer_on_cursor_visibility_changed (MetaCursorTracker  *cursor_tracker,
+                                                   MetaWaylandPointer *pointer)
+{
+  sync_focus_surface (pointer);
+}
+
 void
 meta_wayland_pointer_enable (MetaWaylandPointer *pointer)
 {
@@ -493,6 +508,11 @@ meta_wayland_pointer_enable (MetaWaylandPointer *pointer)
                     "cursor-changed",
                     G_CALLBACK (meta_wayland_pointer_on_cursor_changed),
                     pointer);
+
+  g_signal_connect (cursor_tracker,
+                    "visibility-changed",
+                    G_CALLBACK (meta_wayland_pointer_on_cursor_visibility_changed),
+                    pointer);
 }
 
 void
@@ -505,6 +525,10 @@ meta_wayland_pointer_disable (MetaWaylandPointer *pointer)
                                         (gpointer) meta_wayland_pointer_on_cursor_changed,
                                         pointer);
 
+  g_signal_handlers_disconnect_by_func (cursor_tracker,
+                                        meta_wayland_pointer_on_cursor_visibility_changed,
+                                        pointer);
+
   if (pointer->cursor_surface && pointer->cursor_surface_destroy_id)
     {
       g_signal_handler_disconnect (pointer->cursor_surface,