transparent background on DrawingArea

[michi7x7 <michi michi7x7 de>]

Hello everybody,

I am trying to draw something using Cairo to a DrawingArea and set the 
blank pixels to "transparent" using shape_combine_mask.
With this i want to create a window on desktop-level showing some 
information. To use shape_combine_mask i must create a Gdk::Bitmap from 
the Drawable. Is there a good solution for this?

Regards,

Michael