How to determine (from Elisp) whether the Emacs frame has focus?

[Marcin Borkowski]

Hi all,

I'd like to know whether the selected Emacs frame has focus.  Currently,
I'm using an xdotool/xprop combo (I'm on GNU/Linux), but I'd like to
know whether there is a better way.  I know about focus-in-hook and
focus-out-hook, and I could make them set/unset some global variable,
but this looks hackish.

Any ideas?

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University