Return width, height, x center, and y center for an anchor (window).

def _whctrs(anchor):
        """
        Return width, height, x center, and y center for an anchor (window).
        """
        w = anchor[2] - anchor[0] + 1
        h = anchor[3] - anchor[1] + 1
        x_ctr = anchor[0] + 0.5 * (w - 1)
        y_ctr = anchor[1] + 0.5 * (h - 1)
        return w, h, x_ctr, y_ctr