gdk-window-root-coords (window x y)

window -- a gdk-window object
x -- an integer with the x coordinate in window
y -- an integer with the y coordinate in window

root-x -- an integer with the x root coordinate
root-y -- an integer with the y root coordinate

Obtains the position of a window position in root window coordinates. This is similar to the function gdk-window-origin but allows you to pass in any position in the window, not just the origin.