Add signals for when windows change monitors

This is useful in order to track e.g. which windows are on the primary
monitor.

https://bugzilla.gnome.org/show_bug.cgi?id=609258

src/core/screen.c

@@ -84,6 +84,8 @@ enum
   WORKSPACE_ADDED,
   WORKSPACE_REMOVED,
   WORKSPACE_SWITCHED,
+  WINDOW_ENTERED_MONITOR,
+  WINDOW_LEFT_MONITOR,
   STARTUP_SEQUENCE_CHANGED,
   WORKAREAS_CHANGED,
   MONITORS_CHANGED,
@@ -201,6 +203,28 @@ meta_screen_class_init (MetaScreenClass *klass)
                   G_TYPE_INT,
                   MUTTER_TYPE_MOTION_DIRECTION);
 
+  screen_signals[WINDOW_ENTERED_MONITOR] =
+    g_signal_new ("window-entered-monitor",
+                  G_TYPE_FROM_CLASS (klass),
+                  G_SIGNAL_RUN_LAST,
+                  0,
+                  NULL, NULL,
+                  _mutter_marshal_VOID__INT_OBJECT,
+                  G_TYPE_NONE, 2,
+                  G_TYPE_INT,
+                  META_TYPE_WINDOW);
+
+  screen_signals[WINDOW_LEFT_MONITOR] =
+    g_signal_new ("window-left-monitor",
+                  G_TYPE_FROM_CLASS (klass),
+                  G_SIGNAL_RUN_LAST,
+                  0,
+                  NULL, NULL,
+                  _mutter_marshal_VOID__INT_OBJECT,
+                  G_TYPE_NONE, 2,
+                  G_TYPE_INT,
+                  META_TYPE_WINDOW);
+
   screen_signals[STARTUP_SEQUENCE_CHANGED] =
     g_signal_new ("startup-sequence-changed",
                   G_TYPE_FROM_CLASS (klass),
@@ -2822,6 +2846,21 @@ meta_screen_resize (MetaScreen *screen,
   screen->rect.width = width;
   screen->rect.height = height;
 
+  /* Clear monitor for all windows on this screen, as it will become
+   * invalid. */
+  windows = meta_display_list_windows (screen->display,
+                                       META_LIST_INCLUDE_OVERRIDE_REDIRECT);
+  for (tmp = windows; tmp != NULL; tmp = tmp->next)
+    {
+      MetaWindow *window = tmp->data;
+
+      if (window->screen == screen)
+        {
+          g_signal_emit_by_name (screen, "window-left-monitor", window->monitor->number, window);
+          window->monitor = NULL;
+        }
+    }
+
   reload_monitor_infos (screen);
   set_desktop_geometry_hint (screen);
   

src/core/window.c

@@ -1085,6 +1085,8 @@ meta_window_new_with_attrs (MetaDisplay       *display,
       meta_window_update_struts (window);
     }
 
+  g_signal_emit_by_name (window->screen, "window-entered-monitor", window->monitor->number, window);
+
   /* Must add window to stack before doing move/resize, since the
    * window might have fullscreen size (i.e. should have been
    * fullscreen'd; acrobat is one such braindead case; it withdraws
@@ -1465,6 +1467,13 @@ meta_window_unmanage (MetaWindow  *window,
     }
 #endif
 
+  if (window->monitor)
+    {
+      g_signal_emit_by_name (window->screen, "window-left-monitor",
+                             window->monitor->number, window);
+      window->monitor = NULL;
+    }
+
   if (!window->override_redirect)
     meta_stack_remove (window->screen->stack, window);
 
@@ -4104,6 +4113,10 @@ meta_window_update_monitor (MetaWindow *window)
           meta_window_is_on_primary_monitor (window)  &&
           window->screen->active_workspace != window->workspace)
         meta_window_change_workspace (window, window->screen->active_workspace);
+
+      if (old)
+        g_signal_emit_by_name (window->screen, "window-left-monitor", old->number, window);
+      g_signal_emit_by_name (window->screen, "window-entered-monitor", window->monitor->number, window);
     }
 }
 

src/mutter-marshal.list

@@ -1 +1,2 @@
 VOID:INT,INT,ENUM
+VOID:INT,OBJECT