wayland: Trigger wl_output updates on actor position changes

Both notify::position on the surface actor and position-changed on
MetaWindow are listened to, in order to trigger wl_output updates for
wl_surfaces whenever the surfaces move across them.

Both signals are necessary in order to cater for toplevel and subsurface
relocations (Because it's the parent window actor what changes position
in this last case).

Also, shuffle signal disconnection, so each signal goes away with
the object reference held by MetaWaylandSurface.

https://bugzilla.gnome.org/show_bug.cgi?id=782344

src/wayland/meta-wayland-surface.c

@@ -182,6 +182,13 @@ static void
 surface_actor_allocation_notify (MetaSurfaceActorWayland *surface_actor,
                                  GParamSpec              *pspec,
                                  MetaWaylandSurface      *surface);
+static void
+surface_actor_position_notify (MetaSurfaceActorWayland *surface_actor,
+                               GParamSpec              *pspec,
+                               MetaWaylandSurface      *surface);
+static void
+window_position_changed (MetaWindow         *window,
+                         MetaWaylandSurface *surface);
 
 static void
 unset_param_value (GParameter *param)
@@ -422,13 +429,6 @@ meta_wayland_surface_destroy_window (MetaWaylandSurface *surface)
       MetaDisplay *display = meta_get_display ();
       guint32 timestamp = meta_display_get_current_time_roundtrip (display);
 
-      g_signal_handlers_disconnect_by_func (surface->surface_actor,
-                                            surface_actor_mapped_notify,
-                                            surface);
-      g_signal_handlers_disconnect_by_func (surface->surface_actor,
-                                            surface_actor_allocation_notify,
-                                            surface);
-
       meta_window_unmanage (surface->window, timestamp);
     }
 
@@ -1272,18 +1272,47 @@ meta_wayland_surface_update_outputs (MetaWaylandSurface *surface)
                         surface);
 }
 
+static void
+meta_wayland_surface_update_outputs_recursively (MetaWaylandSurface *surface)
+{
+  GList *l;
+
+  meta_wayland_surface_update_outputs (surface);
+
+  for (l = surface->subsurfaces; l != NULL; l = l->next)
+    meta_wayland_surface_update_outputs_recursively (l->data);
+}
+
 void
 meta_wayland_surface_set_window (MetaWaylandSurface *surface,
                                  MetaWindow         *window)
 {
   gboolean was_unmapped = surface->window && !window;
 
+  if (surface->window == window)
+    return;
+
+  if (surface->window)
+    {
+      g_signal_handlers_disconnect_by_func (surface->window,
+                                            window_position_changed,
+                                            surface);
+    }
+
   surface->window = window;
   sync_reactive (surface);
   sync_drag_dest_funcs (surface);
 
   if (was_unmapped)
     g_signal_emit (surface, surface_signals[SURFACE_UNMAPPED], 0);
+
+  if (window)
+    {
+      g_signal_connect_object (window,
+                               "position-changed",
+                               G_CALLBACK (window_position_changed),
+                               surface, 0);
+    }
 }
 
 static void
@@ -1320,6 +1349,15 @@ wl_surface_destructor (struct wl_resource *resource)
   if (surface->input_region)
     cairo_region_destroy (surface->input_region);
 
+  g_signal_handlers_disconnect_by_func (surface->surface_actor,
+                                        surface_actor_mapped_notify,
+                                        surface);
+  g_signal_handlers_disconnect_by_func (surface->surface_actor,
+                                        surface_actor_allocation_notify,
+                                        surface);
+  g_signal_handlers_disconnect_by_func (surface->surface_actor,
+                                        surface_actor_position_notify,
+                                        surface);
   g_object_unref (surface->surface_actor);
 
   meta_wayland_compositor_destroy_frame_callbacks (compositor, surface);
@@ -1348,7 +1386,7 @@ surface_actor_mapped_notify (MetaSurfaceActorWayland *surface_actor,
                              GParamSpec              *pspec,
                              MetaWaylandSurface      *surface)
 {
-  meta_wayland_surface_update_outputs (surface);
+  meta_wayland_surface_update_outputs_recursively (surface);
 }
 
 static void
@@ -1356,7 +1394,22 @@ surface_actor_allocation_notify (MetaSurfaceActorWayland *surface_actor,
                                  GParamSpec              *pspec,
                                  MetaWaylandSurface      *surface)
 {
-  meta_wayland_surface_update_outputs (surface);
+  meta_wayland_surface_update_outputs_recursively (surface);
+}
+
+static void
+surface_actor_position_notify (MetaSurfaceActorWayland *surface_actor,
+                               GParamSpec              *pspec,
+                               MetaWaylandSurface      *surface)
+{
+  meta_wayland_surface_update_outputs_recursively (surface);
+}
+
+static void
+window_position_changed (MetaWindow         *window,
+                         MetaWaylandSurface *surface)
+{
+  meta_wayland_surface_update_outputs_recursively (surface);
 }
 
 MetaWaylandSurface *
@@ -1381,6 +1434,10 @@ meta_wayland_surface_create (MetaWaylandCompositor *compositor,
                            "notify::allocation",
                            G_CALLBACK (surface_actor_allocation_notify),
                            surface, 0);
+  g_signal_connect_object (surface->surface_actor,
+                           "notify::position",
+                           G_CALLBACK (surface_actor_position_notify),
+                           surface, 0);
   g_signal_connect_object (surface->surface_actor,
                            "notify::mapped",
                            G_CALLBACK (surface_actor_mapped_notify),