[wmx] howto get physical screen size while in xinerama?

Hallo,

I am just trying to change window maximise and placment to work better 
with my to monitor xinerama setup.

I am not much into X programming.
As DisplayWith just returns the virtal (xinerama) size, I wonder if 
there is a way to get size of one screen (monitor) instead.


I also apprciate any pointers to online documentation covering this.

Thanks,
/jan.