def get_normal_points(cx, cy, cos_t, sin_t, length):
    """
    For a line passing through (*cx*, *cy*) and having a angle *t*,
    return locations of the two points located along its perpendicular line at the distance of *length*.
    """

    if length == 0.:
        return cx, cy, cx, cy

    cos_t1, sin_t1 = sin_t, -cos_t
    cos_t2, sin_t2 = -sin_t, cos_t

    x1, y1 = length*cos_t1 + cx, length*sin_t1 + cy
    x2, y2 = length*cos_t2 + cx, length*sin_t2 + cy

    return x1, y1, x2, y2