There are the following possible window types defined in GDK:

 typedef enum
 {
   GDK_WINDOW_ROOT,
   GDK_WINDOW_TOPLEVEL,
   GDK_WINDOW_CHILD,
   GDK_WINDOW_DIALOG,
   GDK_WINDOW_TEMP,
   GDK_WINDOW_FOREIGN
 } GdkWindowType;

Additionally the following type hints may be given:

 typedef enum
 {
   GDK_WINDOW_TYPE_HINT_NORMAL,
   GDK_WINDOW_TYPE_HINT_DIALOG,
   GDK_WINDOW_TYPE_HINT_MENU,
   GDK_WINDOW_TYPE_HINT_TOOLBAR
 } GdkWindowTypeHint;

What do you think which type and hint would suit best?

IMHO, all GIMP windows (e.g. the various tool dialogs) should be
"utility windows". But you can try and play with metacity-window-demo
to find good window types for specific windows.

The "utility window" type is a window manager hint, and is implemented
like this in GTK+:

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  set_gtk_window_type (GTK_WINDOW (window),
"_NET_WM_WINDOW_TYPE_UTILITY");
  gtk_window_set_transient_for (GTK_WINDOW (window), GTK_WINDOW
(parent_window));



Now I see a problem: all "drawing windows" are potential parents for
the dialogs, and a window can only have one parent I believe.
The solution I see is make all "utility windows" childs of the current
"drawing windows" when the latter becomes active.

Err ... I forgot, the implementation of set_gtk_window_type() ...

static void
set_gdk_window_type (GdkWindow  *window,
                     const char *type)
{
  Atom atoms[2] = { None, None };

  atoms[0] = XInternAtom (GDK_WINDOW_XDISPLAY (window),
                          type, False);

  XChangeProperty (GDK_WINDOW_XDISPLAY (window),
                   GDK_WINDOW_XWINDOW (window),
                   XInternAtom (GDK_WINDOW_XDISPLAY (window),
"_NET_WM_WINDOW_TYPE", False),
                   XA_ATOM, 32, PropModeReplace,
                   (guchar *)atoms,
                   1);
}

static void
on_realize_set_type (GtkWindow *window,
                     gpointer   data)
{
  const char *type;

  g_return_if_fail (GTK_WIDGET_REALIZED (window));

  type = g_object_get_data (G_OBJECT (window), "meta-window-type");

  g_return_if_fail (type != NULL);

  set_gdk_window_type (GTK_WIDGET (window)->window,
                       type);
}

static void
set_gtk_window_type (GtkWindow  *window,
                     const char *type)
{
  g_object_set_data (G_OBJECT (window), "meta-window-type", (char*) type);

  g_signal_handlers_disconnect_by_func (G_OBJECT (window),
                                        on_realize_set_type,
                                        NULL);

  g_signal_connect_after (G_OBJECT (window),
                          "realize",
                          G_CALLBACK (on_realize_set_type),
                          NULL);

  if (GTK_WIDGET_REALIZED (window))
    set_gdk_window_type (GTK_WIDGET (window)->window,
                         type);
}

You forgot that The GIMP is not X11 specific. We can't include that
piece of code since it will only work for X11. I also have the
impression that the concept of "utility" windows is specific to the
metacity window manager. We are restricted to the functionality
provided by GDK. I gave you the enums so that you can choose from the
window types that are offered by GDK.

I'm sure that you can find another way to configure your window
manager so that the dock windows behave according to your preferences.
Sawfish for example allows to configure windows according to the
window class and name.

I propose to have this report closed as WONTFIX.

Well, it shouldn't be Metacity-specific (see
http://www.freedesktop.org/standards/wm-spec/1.2/html/x224.html for
the spec), but I agree it should be in gdk instead ...

The HEAD branch of GTK+ seems to have support for these window manager
hints. If GTK+-2.2 is released early enough for GIMP-1.4 we can easily
change this.

2003-03-12  Sven Neumann  <sven@gimp.org>

  * app/widgets/gimpdock.c (gimp_dock_init): set a window type hint
  of GDK_WINDOW_TYPE_HINT_UTILITY for dock windows (fixes bug #94669).

  * app/gui/splash.c (splash_create): set a window type hint of
  GDK_WINDOW_TYPE_HINT_SPLASHSCREEN.

*** Bug 108211 has been marked as a duplicate of this bug. ***