def _quadrant_coord(quadrant, x0, y0, x, y):
    """Return symmetrically reflected coordinates for a given pair."""
    if quadrant == 3:
        return x0 + x, y0 + y
    elif quadrant == 0:
        return x0 + x, y0 - y
    elif quadrant == 2:
        return x0 - x, y0 + y
    elif quadrant == 1:
        return x0 - x, y0 - y
