Drawing lines

["Matthew A. Zeits" <mazeits motown lmco com>]

hello,
I am trying to write a uml case tool using gtk.  I have a question regarding 
drawing 'example' figures and lines.  What I want to do is say draw a line from 
a point pre-selected, to the current position of the pointer, and make sure that 
this line doesn't clobber the items it draws over--i.e. when the line is moved, 
the original pixels in the line's update rectangle are redrawn.  What is the 
easiest way to do this?  I know all the standard methods with other widget 
toolsets, but figuring out how to do it with gtk/gdk is a bit confusing.  I have 
attempted to extract it from the gimp-99.9 selection source, but that has too 
much noise in it for me to extract the idiom.  Thankyou.
Matt Zeits