window: Add window id

Generate a unique 64bit window-id which is unrelated to any windowing
backend.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/306
(cherry picked from commit bbcb66ddf4)

src/core/display-private.h

@@ -507,4 +507,8 @@ void meta_display_notify_pad_group_switch (MetaDisplay        *display,
                                            guint               n_mode,
                                            guint               n_modes);
 
+MetaWindow *meta_display_get_window_from_id (MetaDisplay *display,
+                                             uint64_t     window_id);
+uint64_t    meta_display_generate_window_id (MetaDisplay *display);
+
 #endif

src/core/display.c

@@ -3269,3 +3269,35 @@ meta_display_notify_pad_group_switch (MetaDisplay        *display,
 
   g_string_free (message, TRUE);
 }
+
+MetaWindow *
+meta_display_get_window_from_id (MetaDisplay *display,
+                                 uint64_t     window_id)
+{
+  g_autoptr (GSList) windows = NULL;
+  GSList *l;
+
+  windows = meta_display_list_windows (display, META_LIST_DEFAULT);
+  for (l = windows; l; l = l->next)
+    {
+      MetaWindow *window = l->data;
+
+      if (window->id == window_id)
+        return window;
+    }
+
+  return NULL;
+}
+
+uint64_t
+meta_display_generate_window_id (MetaDisplay *display)
+{
+  static uint64_t base_window_id;
+  static uint64_t last_window_id;
+
+  if (!base_window_id)
+    base_window_id = g_random_int () + 1;
+
+  /* We can overflow here, that's fine */
+  return (base_window_id + last_window_id++);
+}

src/core/window-private.h

@@ -153,6 +153,7 @@ struct _MetaWindow
 
   MetaDisplay *display;
   MetaScreen *screen;
+  uint64_t id;
   guint64 stamp;
   MetaLogicalMonitor *monitor;
   MetaWorkspace *workspace;

src/core/window.c

@@ -1142,6 +1142,8 @@ _meta_window_shared_new (MetaDisplay         *display,
       window->has_resize_func = FALSE;
     }
 
+  window->id = meta_display_generate_window_id (display);
+
   META_WINDOW_GET_CLASS (window)->manage (window);
 
   if (!window->override_redirect)
@@ -8466,3 +8468,17 @@ meta_window_is_stackable (MetaWindow *window)
 {
   return META_WINDOW_GET_CLASS (window)->is_stackable (window);
 }
+
+/**
+ * meta_window_get_id:
+ * @window: a #MetaWindow
+ *
+ * Returns the window id associated with window.
+ *
+ * Returns: (transfer none): The window id
+ */
+uint64_t
+meta_window_get_id (MetaWindow *window)
+{
+  return window->id;
+}

src/meta/window.h

@@ -260,4 +260,6 @@ gboolean meta_window_is_client_decorated (MetaWindow *window);
 gboolean meta_window_titlebar_is_onscreen    (MetaWindow *window);
 void     meta_window_shove_titlebar_onscreen (MetaWindow *window);
 
+uint64_t meta_window_get_id (MetaWindow *window);
+
 #endif