display: Only manage the default X screen

https://bugzilla.gnome.org/show_bug.cgi?id=648156

src/core/display.c

@@ -470,6 +470,7 @@ meta_display_open (void)
 {
   Display *xdisplay;
   GSList *screens;
+  MetaScreen *screen;
   GSList *tmp;
   int i;
   guint32 timestamp;
@@ -854,19 +855,18 @@ meta_display_open (void)
   the_display->last_user_time = timestamp;
   the_display->compositor = NULL;
   
+  /* Mutter used to manage all X screens of the display in a single process, but
+   * now it always manages exactly one screen as specified by the DISPLAY
+   * environment variable. The screens GSList is left for simplicity.
+   */
   screens = NULL;
 
-  i = 0;
-  while (i < ScreenCount (xdisplay))
-    {
-      MetaScreen *screen;
+  i = meta_ui_get_screen_number ();
 
   screen = meta_screen_new (the_display, i, timestamp);
 
   if (screen)
     screens = g_slist_prepend (screens, screen);
-      ++i;
-    }
   
   the_display->screens = screens;
   

src/ui/ui.c

@@ -82,6 +82,12 @@ meta_ui_get_display (void)
   return GDK_DISPLAY_XDISPLAY (gdk_display_get_default ());
 }
 
+gint
+meta_ui_get_screen_number (void)
+{
+  return gdk_screen_get_number (gdk_screen_get_default ());
+}
+
 /* We do some of our event handling in frames.c, which expects
  * GDK events delivered by GTK+.  However, since the transition to
  * client side windows, we can't let GDK see button events, since the

src/ui/ui.h

@@ -46,6 +46,8 @@ void meta_ui_init (void);
 
 Display* meta_ui_get_display (void);
 
+gint meta_ui_get_screen_number (void);
+
 void meta_ui_add_event_func    (Display       *xdisplay,
                                 MetaEventFunc  func,
                                 gpointer       data);