Created attachment 216721 [details] [review]
a proposed patch (works for me)

I have to create some gtk UI a I want to use glade. I've found out that it is not possible to run glade in my KDE desktop with widget style oxygen-gtk. If I click on the new window icon from toolbar glage immeadiately crashes with SIGSEGV.

What I discovered:

glade creates a GDK_WINDOW_OFFSCREEN window and oxygen-gtk wants to get frame
extents for this window. The problem is that it is not possible to get frame
extents of an offscreen window.

Problem description:

The following lines are copied from glade, gtk and oxygen-gtk sources.
The lines show steps to crash.

1. glade creates an attributes for offscreen window
glade_design_layout_realize() : gladeui/glade-design-layout.c : 1630
  attributes.window_type = GDK_WINDOW_OFFSCREEN;

2.
glade_design_layout_realize() : gladeui/glade-design-layout.c : 1644
  ipriv->offscreen_window = gdk_window_new (gtk_widget_get_root_window (widget),
                                            &attributes, attributes_mask);

3.
gdk_window_new () : gdk/gdkwindow.c 11375
  if (gdk_window_is_offscreen (window))
    {
      _gdk_offscreen_window_new (window, attributes, attributes_mask);

4.
gdk_window_is_offscreen() : gdk/gdkwindow.c : 11375
  static gboolean
  gdk_window_is_offscreen (GdkWindow *window)
  {
        return window->window_type == GDK_WINDOW_OFFSCREEN;
  }

5.
_gdk_offscreen_window_new() : gdk/gdkoffscreenwindow.c : 803
  window->impl = g_object_new (GDK_TYPE_OFFSCREEN_WINDOW, NULL);

6.
gdk_offscreen_window_class_init() : gdk/gdkoffscreenwindow.c : 766
  impl_class->get_frame_extents = NULL;

-- And finally.

7.
Gtk::gdk_toplevel_get_frame_size() : src/oxygengtkutils.cpp : 882
  gdk_window_get_frame_extents( topLevel, &rect );

8.
gdk_window_get_frame_extents() : gdk/gdkwindow.c : 10443
  GDK_WINDOW_IMPL_GET_CLASS (window->impl)->get_frame_extents (window, rect);
                                               
-- Ooops, get_frame_extents is NULL here

Backtrace:

+ Trace 230387