If a certain section of the curve is straight, the end points of the line have a maximum of one control point each. They cannot be modified to round points unless the straight line is converted back to a curve.
如果曲线中的一部分是直线段，那么该直线段的每个端点最多只有一个控制点。您可能做不出圆滑接点来，这是因为先把该直线重新转换为曲线了。