posn-object-x-y

posn-object-x-y is a compiled Lisp function in `subr.el'.

(posn-object-x-y POSITION)

Return the x and y coordinates relative to the object of POSITION.
The return value has the form (DX . DY), where DX and DY are
given in pixels. POSITION should be a list of the form returned
by `event-start' and `event-end'.