Add meta_window_get_stable_sequence

Useful for plugins which want to order windows in a stable
fashion.

https://bugzilla.gnome.org/show_bug.cgi?id=595882

src/core/display-private.h

@@ -150,6 +150,15 @@ struct _MetaDisplay
   
   guint32 current_time;
 
+  /* We maintain a sequence counter, incremented for each #MetaWindow
+   * created.  This is exposed by meta_window_get_stable_sequence()
+   * but is otherwise not used inside mutter.
+   *
+   * It can be useful to plugins which want to sort windows in a
+   * stable fashion.
+   */
+  guint32 window_sequence_counter;
+
   /* Pings which we're waiting for a reply from */
   GSList     *pending_pings;
 

src/core/window-private.h

@@ -316,6 +316,9 @@ struct _MetaWindow
    */
   int unmaps_pending;
 
+  /* See docs for meta_window_get_stable_sequence() */
+  guint32 stable_sequence;
+
   /* set to the most recent user-interaction event timestamp that we
      know about for this window */
   guint32 net_wm_user_time;

src/core/window.c

@@ -802,6 +802,10 @@ meta_window_new_with_attrs (MetaDisplay       *display,
 
   meta_display_register_x_window (display, &window->xwindow, window);
 
+  /* Assign this #MetaWindow a sequence number which can be used
+   * for sorting.
+   */
+  window->stable_sequence = ++display->window_sequence_counter;
 
   /* assign the window to its group, or create a new group if needed
    */
@@ -8532,6 +8536,26 @@ meta_window_set_user_time (MetaWindow *window,
   g_object_notify (G_OBJECT (window), "user-time");
 }
 
+/**
+ * meta_window_get_stable_sequence:
+ * @window: A #MetaWindow
+ *
+ * The stable sequence number is a monotonicially increasing
+ * unique integer assigned to each #MetaWindow upon creation.
+ *
+ * This number can be useful for sorting windows in a stable
+ * fashion.
+ *
+ * Returns: Internal sequence number for this window
+ */
+guint32
+meta_window_get_stable_sequence (MetaWindow *window)
+{
+  g_return_val_if_fail (META_IS_WINDOW (window), 0);
+
+  return window->stable_sequence;
+}
+
 /* Sets the demands_attention hint on a window, but only
  * if it's at least partially obscured (see #305882).
  */

src/include/window.h

@@ -118,6 +118,7 @@ const char *meta_window_get_title (MetaWindow *window);
 MetaWindow *meta_window_get_transient_for (MetaWindow *window);
 void        meta_window_delete             (MetaWindow  *window,
                                             guint32      timestamp);
+guint       meta_window_get_stable_sequence (MetaWindow *window);
 guint32     meta_window_get_user_time (MetaWindow *window);
 int         meta_window_get_pid (MetaWindow *window);
 const char *meta_window_get_client_machine (MetaWindow *window);