How to put the GtkWidget to max screen size?

["alan" <alan ielinux com>]

I set GtkWidget to max size of screen by use gtk_widget_set_usize() and
gtk_widget_set_uposition().
If I running in kde environmentis is ok.
but if I set widget position to (0,0), and running program in afterstop.
The title bar of afterstep will hide over screen.
Have any other way to set GtkWidget to max size of screen.
And, How to know the border size and title bar height of window manager?