drawing the entire window or pars of it?

[lchen patrick com au]

My applcation tracks vehicle movement in real time.   All objects
are in 2-D.

It seems to me the hard bit is - recover the scene at location "A"
when the vehicle has moved to "B".   The porgram needs to find
out all the objects or parts of the objects covered by the vehicle
while it was at "A" and redraw them.   I kind of remember reading
from somewhere that one can just redraw the entire objects off screen
and then copy/swap it over.  Is this the right way of doing it?
Will it slow things down?
Or I have to keep track of what regions need to be redrawn, which
is really tedious.   Does GDK/GTK+ manage the objects too?

Also, is it possible to associate a function to a drawable on the display?
eg. the function is called when user clicks on a polygon.

Thanks.