'return x, y (in display coordinate) that is to be used for a reference
of any offset coordinate'

def _get_ref_xy(self, renderer):

    if isinstance(self.xycoords, tuple):
        (s1, s2) = self.xycoords
        if ((isinstance(s1, six.string_types) and (s1.split()[0] == u'offset')) or (isinstance(s2, six.string_types) and (s2.split()[0] == u'offset'))):
            raise ValueError(u'xycoords    should    not    be    an    offset    coordinate')
        (x, y) = self.xy
        (x1, y1) = self._get_xy(renderer, x, y, s1)
        (x2, y2) = self._get_xy(renderer, x, y, s2)
        return (x1, y2)
    elif (isinstance(self.xycoords, six.string_types) and (self.xycoords.split()[0] == u'offset')):
        raise ValueError(u'xycoords    should    not    be    an    offset    coordinate')
    else:
        (x, y) = self.xy
        return self._get_xy(renderer, x, y, self.xycoords)
