ios - 无法在同一个 CGMutablePathRef 上创建两个 CGPathAddArc

Question

我试图理解为什么我只看到我的一个 CGPathAddArc。

代码:

  var r: CGRect = self.myView.bounds
 var lay: CAShapeLayer = CAShapeLayer()
        var path: CGMutablePathRef = CGPathCreateMutable()
        CGPathAddArc(path, nil, 30, 30, 30, 0, (360 * CGFloat(M_PI))/180, true    )
        CGPathAddArc(path, nil, 70, 30, 30, 0, (360 * CGFloat(M_PI))/180, true    )

        CGPathAddRect(path, nil, r2)
 CGPathAddRect(path, nil, r)
        lay.path = path
        lay.fillRule = kCAFillRuleEvenOdd
        self.myView.layer.mask = lay

结果:

有什么建议吗？谢谢!

Answer 1

如果您按下命令键并单击 CGPathAddArc 函数，您将看到文档。

/* Note that using values very near 2π can be problematic. For example,
   setting `startAngle' to 0, `endAngle' to 2π, and `clockwise' to true will
   draw nothing. (It's easy to see this by considering, instead of 0 and 2π,
   the values ε and 2π - ε, where ε is very small.) Due to round-off error,
   however, it's possible that passing the value `2 * M_PI' to approximate
   2π will numerically equal to 2π + δ, for some small δ; this will cause a
   full circle to be drawn.

   If you want a full circle to be drawn clockwise, you should set
   `startAngle' to 2π, `endAngle' to 0, and `clockwise' to true. This avoids
   the instability problems discussed above. */

将 startAngle 设置为 0，将 endAngle 设置为 2π，并将 clockwise 设置为 true什么都不画。如果你想顺时针绘制一个完整的圆，你应该设置 startAngle 为 2π，endAngle 为 0，clockwise 为 true。这样你就可以看到所有的圈子。