drawing area widget repainting

[lost <lost paradise net nz>]

How do I force a drawing area widget to redraw a sub-section of itself
and clear the area to the default background colour at the same time?

there is:
        gtk_widget_queue_draw_area(); 
which forces the redraw, but dosn't clear the exposed area first
        gtk_widget_queue_clear_area();
doesn't appear to do anything.

At present, I'm clearing the area by drawing a filled rectangle over it
in the same colour as the default background, but I'd like to find the
proper method

Thanks

--
Jacob Lister, home in Wellington, New Zealand,
Author, Carbon audio processing software :
  http://homepages.paradise.net.nz/lost