widget: Track when the window scale factor changes and notify

The scale-factor property on the widgets will be notified, and the
scale will change on the style property, causing us to pick up
new css assets.

gtk/gtkwidget.c

@@ -9992,10 +9992,33 @@ gtk_widget_has_screen (GtkWidget *widget)
   return (gtk_widget_get_screen_unchecked (widget) != NULL);
 }
 
+void
+_gtk_widget_scale_changed (GtkWidget *widget)
+{
+  GtkWidgetPrivate *priv;
+
+  g_return_if_fail (GTK_IS_WIDGET (widget));
+
+  priv = widget->priv;
+
+  if (priv->context)
+    gtk_style_context_set_scale (priv->context, gtk_widget_get_scale_factor (widget));
+
+  g_object_notify (G_OBJECT (widget), "scale-factor");
+
+  gtk_widget_queue_draw (widget);
+
+  if (GTK_IS_CONTAINER (widget))
+    gtk_container_forall (GTK_CONTAINER (widget),
+                          (GtkCallback) _gtk_widget_scale_changed,
+                          NULL);
+}
+
 gint
 gtk_widget_get_scale_factor (GtkWidget *widget)
 {
   GtkWidget *toplevel;
+  GdkScreen *screen;
 
   g_return_val_if_fail (GTK_IS_WIDGET (widget), 1);
 
@@ -10009,7 +10032,11 @@ gtk_widget_get_scale_factor (GtkWidget *widget)
   /* else fall back to something that is more likely to be right than
    * just returning 1:
    */
-  return gdk_screen_get_monitor_scale_factor (gtk_widget_get_screen (widget), 0);
+  screen = gtk_widget_get_screen (widget);
+  if (screen)
+    return gdk_screen_get_monitor_scale_factor (screen, 0);
+
+  return 1;
 }
 
 /**

gtk/gtkwidgetprivate.h

@@ -47,6 +47,8 @@ void         _gtk_widget_set_alloc_needed   (GtkWidget *widget,
                                              gboolean   alloc_needed);
 void         _gtk_widget_draw               (GtkWidget *widget,
 					     cairo_t   *cr);
+void          _gtk_widget_scale_changed     (GtkWidget *widget);
+
 
 void         _gtk_widget_add_sizegroup         (GtkWidget    *widget,
 						gpointer      group);

gtk/gtkwindow.c

@@ -147,6 +147,8 @@ struct _GtkWindowPrivate
 
   guint    mnemonics_display_timeout_id;
 
+  gint     scale;
+
   gint title_height;
   GtkWidget *title_box;
   GtkWidget *title_icon;
@@ -1335,6 +1337,8 @@ gtk_window_init (GtkWindow *window)
 
   context = gtk_widget_get_style_context (GTK_WIDGET (window));
   gtk_style_context_add_class (context, GTK_STYLE_CLASS_BACKGROUND);
+
+  priv->scale = gtk_widget_get_scale_factor (GTK_WIDGET (window));
 }
 
 static void
@@ -5689,6 +5693,7 @@ gtk_window_realize (GtkWidget *widget)
   gint attributes_mask;
   GtkWindowPrivate *priv;
   gint i;
+  int old_scale;
 
   window = GTK_WINDOW (widget);
   priv = window->priv;
@@ -5918,6 +5923,11 @@ gtk_window_realize (GtkWidget *widget)
 
   if (priv->has_resize_grip)
     resize_grip_create_window (window);
+
+  old_scale = priv->scale;
+  priv->scale = gtk_widget_get_scale_factor (widget);
+  if (old_scale != priv->scale)
+    _gtk_widget_scale_changed (widget);
 }
 
 static void
@@ -6515,6 +6525,12 @@ gtk_window_configure_event (GtkWidget         *widget,
   GtkWindow *window = GTK_WINDOW (widget);
   GtkWindowPrivate *priv = window->priv;
   gboolean expected_reply = priv->configure_request_count > 0;
+  int old_scale;
+
+  old_scale = priv->scale;
+  priv->scale = gtk_widget_get_scale_factor (widget);
+  if (old_scale != priv->scale)
+    _gtk_widget_scale_changed (widget);
 
   if (!gtk_widget_is_toplevel (GTK_WIDGET (widget)))
     {
@@ -9681,6 +9697,7 @@ gtk_window_set_screen (GtkWindow *window,
   GtkWidget *widget;
   GdkScreen *previous_screen;
   gboolean was_mapped;
+  int old_scale;
 
   g_return_if_fail (GTK_IS_WINDOW (window));
   g_return_if_fail (GDK_IS_SCREEN (screen));
@@ -9728,6 +9745,11 @@ gtk_window_set_screen (GtkWindow *window,
 
   if (was_mapped)
     gtk_widget_map (widget);
+
+  old_scale = priv->scale;
+  priv->scale = gtk_widget_get_scale_factor (widget);
+  if (old_scale != priv->scale)
+    _gtk_widget_scale_changed (widget);
 }
 
 static void