GdkPixbuf and gtk_widget_shape_combine_mask()

[Trevor Spiteri <tspiteri falmalta com>]

gtk_widget_shape_combine_mask() requires a GdkBitmap * parameter. How do
I get such a GdkBitmap * when I have a GdkPixbuf *?

I tried to use gdk_pixbuf_render_pixmap_and_mask(), but could not figure
a way to unref the resulting pixmap and bitmap after using
gtk_widget_shape_combine_mask(). This is because I use
GDK_DISABLE_DEPRECATED, so gdk_pixmap_unref(), gdk_bitmap_unref() and
gdk_drawable_unref() are all disabled. Is there a non-deprecated way to
unref the pixmap and bitmap?

Thanks

Trevor Spiteri