[gtk+] x11: Make selection handling work across screens

[Matthias Clasen <matthiasc src gnome org>]

commit 55edc81c10742bf3e410168f6dc317f8aca05938
Author: Matthias Clasen <mclasen redhat com>
Date:   Mon Jul 27 23:18:27 2015 -0400

    x11: Make selection handling work across screens
    
    When dealing with selection events, we might see windows from
    other screens in the requestor field. The current x11 backend
    code fails to wrap these in a foreign GdkWindow, since we
    don't have the corresponding GdkScreen anymore. Work around
    this by creating such 'foreign screens' on demand. We still
    maintain the 1:1 relation between the display and the screen
    returned by gdk_display_get_default_screen().
    
    https://bugzilla.gnome.org/show_bug.cgi?id=721398

 gdk/x11/gdkdisplay-x11.c |   29 +++++++++++++++++++++++++++--
 gdk/x11/gdkdisplay-x11.h |    1 +
 2 files changed, 28 insertions(+), 2 deletions(-)
---
diff --git a/gdk/x11/gdkdisplay-x11.c b/gdk/x11/gdkdisplay-x11.c
index f2824b6..9bb27ee 100644
--- a/gdk/x11/gdkdisplay-x11.c
+++ b/gdk/x11/gdkdisplay-x11.c
@@ -1959,6 +1959,7 @@ gdk_x11_display_finalize (GObject *object)
 
   /* Free all GdkScreens */
   g_object_unref (display_x11->screen);
+  g_list_free_full (display_x11->screens, g_object_unref);
 
   g_free (display_x11->startup_notification_id);
 
@@ -2035,12 +2036,36 @@ GdkScreen *
 _gdk_x11_display_screen_for_xrootwin (GdkDisplay *display,
                                      Window      xrootwin)
 {
-  GdkScreen *screen = gdk_display_get_default_screen (display);
+  GdkScreen *screen;
+  XWindowAttributes attrs;
+  gboolean result;
+  GdkX11Display *display_x11;
+  GList *l;
+
+  screen = gdk_display_get_default_screen (display);
 
   if (GDK_SCREEN_XROOTWIN (screen) == xrootwin)
     return screen;
 
-  return NULL;
+  display_x11 = GDK_X11_DISPLAY (display);
+
+  for (l = display_x11->screens; l; l = l->next)
+    {
+      screen = l->data;
+      if (GDK_SCREEN_XROOTWIN (screen) == xrootwin)
+        return screen;
+    }
+
+  gdk_x11_display_error_trap_push (display);
+  result = XGetWindowAttributes (display_x11->xdisplay, xrootwin, &attrs);
+  if (gdk_x11_display_error_trap_pop (display) || !result)
+    return NULL;
+
+  screen = _gdk_x11_screen_new (display, XScreenNumberOfScreen (attrs.screen));
+
+  display_x11->screens = g_list_prepend (display_x11->screens, screen);
+
+  return screen;
 }
 
 /**
diff --git a/gdk/x11/gdkdisplay-x11.h b/gdk/x11/gdkdisplay-x11.h
index aadf255..9b78f61 100644
--- a/gdk/x11/gdkdisplay-x11.h
+++ b/gdk/x11/gdkdisplay-x11.h
@@ -39,6 +39,7 @@ struct _GdkX11Display
   GdkDisplay parent_instance;
   Display *xdisplay;
   GdkScreen *screen;
+  GList *screens;
 
   GSource *event_source;