def _corners(d):
    """Return corner coordinates.

    @param d: `dict` with keys
        `'x', 'y', 'w', 'h'`
    @return: quadruple
    @rtype: `tuple`
    """
    x = d['x']
    y = d['y']
    w = d['w']
    h = d['h']
    xmax = x + w
    ymax = y + h
    return x, xmax, y, ymax