Window Questions

[osiris@cs.utexas.edu]

Several quick (hopefully) questions:

Try this: make an instance of a window, start a picture in that window, and
then flip that window from foreground to background a few times.  Now get
the picture.  You will notice that the picture will vary in size depending
on the number of times that you obscured and uncovered the window even
though you never sent a single drawing command to the window.  This happens
even if the erase-anonymous-invalidations initarg is false.  Why?  What are
the drawing commands that are being sent to the window and is there a way
to strip them out?

here is the code more or less

(require 'quickdraw)
(setf xxx (make-instance 'window :color-p T :erase-anonymous-invalidations ()))
(start-picture xxx)
;;; now flip to another app and back a few times
(setf ggg (get-picture xxx))
;;; note the size of the handle...

Also is there a method that is called when a window is about to go into the
background, or come to the foreground?

Thanks.