#include <stdio.h>
#include <X11/Xlib.h>

int main()
{
  Display *d;
  Window inwin;      /* root window the pointer is in */
  Window inchildwin; /* child win the pointer is in */
  int rootx, rooty; /* relative to the "root" window; we are not interested in these,
                       but we can't pass NULL */
  int childx, childy;  /* the values we are interested in */
  Atom atom_type_prop; /* not interested */
  int actual_format;   /* should be 32 after the call */
  unsigned int mask;   /* status of the buttons */
  unsigned long n_items, bytes_after_ret;
  Window *props; /* since we are interested just in the first value, which is
		    a Window id */

  /* default DISPLAY */
  d = XOpenDisplay(NULL);

  /* ask for active window (no error check); the client must be freedesktop
     compliant */
  (void)XGetWindowProperty(d, DefaultRootWindow(d),
			   XInternAtom(d, "_NET_ACTIVE_WINDOW", True),
			   0, 1, False, AnyPropertyType,
			   &atom_type_prop, &actual_format,
			   &n_items, &bytes_after_ret, (unsigned char**)&props);
			
  XQueryPointer(d, props[0], &inwin,  &inchildwin,
		&rootx, &rooty, &childx, &childy, &mask);
  printf("relative to active window: %d,%d\n", childx, childy);

  XFree(props);           /* free mem */
  (void)XCloseDisplay(d); /* and close the display */
  return 0;
}