Accessor function for application.width ?

[N James Bridge <james xmas demon co uk>]

It's useful to blank out a drawing area by drawing a filled rectangle
with the same size as the window. The examples I have seen get the
dimensions from widget->allocation.width but Devhelp says that the
GtkAllocation structure is GSEALed. At present the method works but is
there an accessor function to use instead? I can't find one.

TIA

James