backends: add 'monitors-updated-internal' signal to only update internal state

Adding an internal signal and use it to update the internal state before
emitting "monitors-changed" which will be repeated by the screen to the world.

https://bugzilla.gnome.org/show_bug.cgi?id=788860

src/backends/meta-backend.c

@@ -196,8 +196,6 @@ meta_backend_monitors_changed (MetaBackend *backend)
           priv->is_pointer_position_initialized = TRUE;
         }
     }
-
-  meta_settings_update_ui_scaling_factor (priv->settings);
 }
 
 void

src/backends/meta-input-settings.c

@@ -1617,7 +1617,7 @@ meta_input_settings_init (MetaInputSettings *settings)
     g_hash_table_new_full (NULL, NULL, NULL, (GDestroyNotify) device_mapping_info_free);
 
   priv->monitor_manager = g_object_ref (meta_monitor_manager_get ());
-  g_signal_connect (priv->monitor_manager, "monitors-changed",
+  g_signal_connect (priv->monitor_manager, "monitors-changed-internal",
                     G_CALLBACK (monitors_changed_cb), settings);
 
 #ifdef HAVE_LIBWACOM

src/backends/meta-monitor-manager.c

@@ -59,6 +59,7 @@ enum
 static GParamSpec *obj_props[PROP_LAST];
 
 enum {
+  MONITORS_CHANGED_INTERNAL,
   CONFIRM_DISPLAY_CHANGE,
   SIGNALS_LAST
 };
@@ -838,6 +839,14 @@ meta_monitor_manager_class_init (MetaMonitorManagerClass *klass)
   klass->read_edid = meta_monitor_manager_real_read_edid;
   klass->is_lid_closed = meta_monitor_manager_real_is_lid_closed;
 
+  signals[MONITORS_CHANGED_INTERNAL] =
+    g_signal_new ("monitors-changed-internal",
+                  G_TYPE_FROM_CLASS (object_class),
+                  G_SIGNAL_RUN_LAST,
+                  0,
+                  NULL, NULL, NULL,
+                  G_TYPE_NONE, 0);
+
   signals[CONFIRM_DISPLAY_CHANGE] =
     g_signal_new ("confirm-display-change",
 		  G_TYPE_FROM_CLASS (object_class),
@@ -2624,6 +2633,7 @@ meta_monitor_manager_notify_monitors_changed (MetaMonitorManager *manager)
 
   meta_backend_monitors_changed (manager->backend);
 
+  g_signal_emit (manager, signals[MONITORS_CHANGED_INTERNAL], 0);
   g_signal_emit_by_name (manager, "monitors-changed");
 }
 

src/backends/meta-screen-cast-monitor-stream.c

@@ -130,7 +130,7 @@ meta_screen_cast_monitor_stream_new (GDBusConnection     *connection,
 
   monitor_stream->stage = stage;
 
-  g_signal_connect_object (monitor_manager, "monitors-changed",
+  g_signal_connect_object (monitor_manager, "monitors-changed-internal",
                            G_CALLBACK (on_monitors_changed),
                            monitor_stream, 0);
 

src/backends/meta-settings.c

@@ -343,11 +343,25 @@ meta_settings_init (MetaSettings *settings)
   update_experimental_features (settings);
 }
 
+static void
+on_monitors_changed (MetaMonitorManager *monitor_manager,
+                     MetaSettings       *settings)
+{
+  meta_settings_update_ui_scaling_factor (settings);
+}
+
 void
 meta_settings_post_init (MetaSettings *settings)
 {
+  MetaMonitorManager *monitor_manager =
+    meta_backend_get_monitor_manager (settings->backend);
+
   update_ui_scaling_factor (settings);
   update_font_dpi (settings);
+
+  g_signal_connect_object (monitor_manager, "monitors-changed-internal",
+                           G_CALLBACK (on_monitors_changed),
+                           settings, G_CONNECT_AFTER);
 }
 
 static void

src/backends/native/meta-cursor-renderer-native.c

@@ -1071,7 +1071,7 @@ meta_cursor_renderer_native_new (MetaBackend *backend)
   priv =
     meta_cursor_renderer_native_get_instance_private (cursor_renderer_native);
 
-  g_signal_connect_object (monitor_manager, "monitors-changed",
+  g_signal_connect_object (monitor_manager, "monitors-changed-internal",
                            G_CALLBACK (on_monitors_changed),
                            cursor_renderer_native, 0);
 

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

@@ -454,7 +454,7 @@ meta_backend_x11_post_init (MetaBackend *backend)
   META_BACKEND_CLASS (meta_backend_x11_parent_class)->post_init (backend);
 
   monitor_manager = meta_backend_get_monitor_manager (backend);
-  g_signal_connect (monitor_manager, "monitors-changed",
+  g_signal_connect (monitor_manager, "monitors-changed-internal",
                     G_CALLBACK (on_monitors_changed), backend);
 }