Strange transparency behaviour

[Miguel Gómez <magomez igalia com>]

Hi!

I was making some trials with transparency stuff with the code attached, 
 and I've found that if I put an eventbox in a window and set its 
background transparent, the background of the window becomes transparent 
too.

Is this the normal behaviour? I was expecting to see the window 
background through the eventbox. Is there any way to handle the opacity 
of the window background and of the eventbox separately? Or maybe there 
is only one alpha channel per toplevel window and it's impossible to set 
different opacities to different gdkwindows that are in the same window 
hierarchy?

Thanks for your help!

Greetings!

--
Miguel Gomez <magomez igalia com>
Igalia - http://www.igalia.com

#include <gtk/gtk.h>


static gboolean
transparent_expose (GtkWidget      *widget,
                    GdkEventExpose *event)
{
  cairo_t *cr;

  cr = gdk_cairo_create (widget->window);
  cairo_set_operator (cr, CAIRO_OPERATOR_CLEAR);
  gdk_cairo_region (cr, event->region);
  cairo_fill (cr);
  cairo_destroy (cr);

  return FALSE;
}


int
main (int argc, char **argv)
{
    GtkWidget *window, *event, *label, *aspect;
  GdkScreen *screen;
  GdkColormap *rgba;

  gtk_init (&argc, &argv);


  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  screen = gtk_widget_get_screen (window);
  rgba = gdk_screen_get_rgba_colormap (screen);
  gtk_widget_set_colormap (window, rgba);
  gtk_widget_set_size_request (window, 300, 300);

  aspect = gtk_aspect_frame_new (NULL, 0.5, 0.5, 4.0 / 3, FALSE);
  gtk_container_add (GTK_CONTAINER (window), aspect);
  
  event = gtk_event_box_new ();
  gtk_event_box_set_visible_window (GTK_EVENT_BOX (event), TRUE);
  gtk_widget_set_app_paintable (GTK_WIDGET (event), TRUE);
  gtk_container_add (GTK_CONTAINER (aspect), event);
  g_signal_connect (event, "expose-event",
                    G_CALLBACK (transparent_expose), NULL);

  label = gtk_label_new ("this a visible label");
  gtk_container_add (GTK_CONTAINER (event), label);
  
  gtk_widget_show_all (window);
  
  gtk_main ();

  return 0;
}