Don't create ALL BackgroundWindows new if monitors change

Author: leolost2605

src/ShellClients/BackgroundWindow.vala

@@ -25,10 +25,14 @@ public class Gala.BackgroundWindow : Object {
 
         providing_window = new_window;
 
+        providing_window.unmanaging.connect (on_window_unmanaging);
+
+        reposition ();
+    }
+
+    public void reposition () {
         var monitor_geom = display.get_monitor_geometry (monitor_index);
         providing_window.move_frame (false, monitor_geom.x, monitor_geom.y);
-
-        providing_window.unmanaging.connect (on_window_unmanaging);
     }
 
     private void on_window_unmanaging () {

src/ShellClients/ShellClientsManager.vala

@@ -53,9 +53,14 @@ public class Gala.ShellClientsManager : Object {
     private void update_background_windows () {
         var display = wm.get_display ();
 
-        background_windows = new BackgroundWindow[display.get_n_monitors ()];
+        background_windows.resize (display.get_n_monitors ());
+
         for (int i = 0; i < background_windows.length; i++) {
-            background_windows[i] = new BackgroundWindow (display, i);
+            if (background_windows[i] == null) {
+                background_windows[i] = new BackgroundWindow (display, i);
+            } else {
+                background_windows[i].reposition ();
+            }
         }
     }