Transparent Background
What about transparent backgrounds? In order to have some areas of the window appear transparent, you need to apply a shape mask to it. A shape mask is a GdkBitmap specifying which pixels will appear transparent and which - opaque. Note that GdkBitmap is a monochrome mask so it is not possible to achieve variable transparency as of yet. Complete example: 

 1: <?php
 2:   $win = &new GtkWindow();
 3:   $win->realize();
 4: 
 5:   list($pixmap, $mask) =
 6:      gdk::pixmap_create_from_xpm($win->window, null, "rings.xpm");
 7: 
 8:   $pix = &new GtkPixmap($pixmap, $mask);
 9: 
10:   $win->add($pix);
11:   $win->shape_combine_mask($mask, 0, 0);
12: 
13:   $win->set_default_size($pixmap->width, $pixmap->height);
14:   $win->set_policy(false, false, false);
15:   $win->show_all();
16: ?>