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

@@ -46,6 +46,7 @@
 #define DEFAULT_DISPLAY_CONFIGURATION_TIMEOUT 20
 
 enum {
+  MONITORS_CHANGED_INTERNAL,
   CONFIRM_DISPLAY_CHANGE,
   SIGNALS_LAST
 };
@@ -851,6 +852,14 @@ 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),
@@ -2574,6 +2583,8 @@ meta_monitor_manager_notify_monitors_changed (MetaMonitorManager *manager)
   manager->current_switch_config = META_MONITOR_SWITCH_CONFIG_UNKNOWN;
 
   meta_backend_monitors_changed (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

@@ -850,7 +850,7 @@ meta_cursor_renderer_native_init (MetaCursorRendererNative *native)
   MetaMonitorManager *monitors;
 
   monitors = meta_monitor_manager_get ();
-  g_signal_connect_object (monitors, "monitors-changed",
+  g_signal_connect_object (monitors, "monitors-changed-internal",
                            G_CALLBACK (on_monitors_changed), native, 0);
 
   priv->hw_state_invalidated = TRUE;

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);
 }
 

src/core/screen.c

@@ -73,8 +73,10 @@ static void prefs_changed_callback (MetaPreference pref,
 static void set_desktop_geometry_hint (MetaScreen *screen);
 static void set_desktop_viewport_hint (MetaScreen *screen);
 
-static void on_monitors_changed (MetaMonitorManager *manager,
+static void on_monitors_changed_internal (MetaMonitorManager *manager,
-                                 MetaScreen         *screen);
+                                          MetaScreen         *screen);
+static void on_monitors_changed          (MetaMonitorManager *manager,
+                                          MetaScreen         *screen);
 
 enum
 {
@@ -710,6 +712,8 @@ meta_screen_new (MetaDisplay *display,
   screen->rect.x = screen->rect.y = 0;
 
   manager = meta_monitor_manager_get ();
+  g_signal_connect (manager, "monitors-changed-internal",
+                    G_CALLBACK (on_monitors_changed_internal), screen);
   g_signal_connect (manager, "monitors-changed",
                     G_CALLBACK (on_monitors_changed), screen);
 
@@ -2266,8 +2270,8 @@ meta_screen_resize_func (MetaWindow *window,
 }
 
 static void
-on_monitors_changed (MetaMonitorManager *manager,
+on_monitors_changed_internal (MetaMonitorManager *manager,
-                     MetaScreen         *screen)
+                              MetaScreen         *screen)
 {
   MetaBackend *backend;
   MetaCursorRenderer *cursor_renderer;
@@ -2306,7 +2310,13 @@ on_monitors_changed (MetaMonitorManager *manager,
   backend = meta_get_backend ();
   cursor_renderer = meta_backend_get_cursor_renderer (backend);
   meta_cursor_renderer_force_update (cursor_renderer);
+}
 
+static void
+on_monitors_changed (MetaMonitorManager *manager,
+                     MetaScreen         *screen)
+{
+  /* Inform the external world about what has happened */
   g_signal_emit (screen, screen_signals[MONITORS_CHANGED], 0);
 }
 

src/wayland/meta-wayland-outputs.c

@@ -422,7 +422,7 @@ meta_wayland_outputs_init (MetaWaylandCompositor *compositor)
   MetaMonitorManager *monitors;
 
   monitors = meta_monitor_manager_get ();
-  g_signal_connect (monitors, "monitors-changed",
+  g_signal_connect (monitors, "monitors-changed-internal",
                     G_CALLBACK (on_monitors_changed), compositor);
 
   compositor->outputs = g_hash_table_new_full (NULL, NULL, NULL, wayland_output_destroy_notify);