'Midpoint of rectangle edges from left, moving clockwise.'

@property
def edge_centers(self):

    (x0, y0, width, height) = self._rect_bbox
    w = (width / 2.0)
    h = (height / 2.0)
    xe = (x0, (x0 + w), (x0 + width), (x0 + w))
    ye = ((y0 + h), y0, (y0 + h), (y0 + height))
    return (xe, ye)
