console switching

[<cw...@so...>]

just a quick curiosity:
how does one detect when a console switch occurs?  we are writing an 
application that needs to stop drawing on the framebuffer when it is no longer 
in the correct console. (ie, we run app in console 1, we then switch to console 
2.  app needs to not draw all over console 2's screen (1 fb device))

normally, i would try to avoid such a dumb question, but i haven't found an 
obvious solution immediatly.

thanks in advance =)

chris