drawing without deleting backgound

[Andreas Volz <andreas brachttal net>]

Hi,

I''ve drawn some background graphics in my gtk 2.0 application into an
GdkPixmap and then copy it into the drawing_area like in the
scribble-example.

But now I want to draw some complex objects on the background and move
them without deleting the background image. I know from my old Borland C
BGI days that I must create a mask for my new object, then copy the
background under the mask to a temp_image and later copy it back. Right?

But how could I do it in gdk? Which functions should I use to do it?

Or is there a better way do to it? Perhaps a second layer or moving a
second image with an alpha mask around, ...?

Any examples?

I develop with an linux X-Window System, but later I'll port the
application to Windows. Are there any restrictions to gdk on Windows?

Thanks
Andreas