Howto get notified when an GdkWindow becomes invisible?

["Clemens Eisserer" <linuxhippy gmail com>]

Hello,

sorry for bothering you again, I already asked this on gtk-list, but
maybe it was the wrong list and maybe therefor I got no answer.

I would like to release some resources as soon as a GdkWindow is set
to a state where it has never to paint itself (=hidden, minimized,
...) and I am seeking for advice - whats the best way to do this? I
plan to do this in GdkWindow.c itself, so are there better ways than
to register a signal? Which events should I listen to?

Thank you in advance, lg Clemens