GdkFunction and GdkLineStyle

[Rok Roskar <rroskar artsci wustl edu>]

Can someone please give me an example using GdkFunction and GdkLineStyle?
I am trying to draw a selection rectangle on top of an image, preferably
so that the pixels comprising the rectangle would be the negative of the
underlying image pixels... I thou~ght that this could be done using the
GdkFunction and GDK_INVERT, but I cant figure out the syntax.... thanks
for the help,

Rok