ios - UIBezierPath 的开始和结束角度？

Question

我使用 UIBezierPath 和 CAShapeLayer 在 iOS 中为半圆编码如下。

 clockWiseLayer = [[CAShapeLayer alloc] init];

CGFloat startAngle = -M_PI_2;
CGFloat endAngle = M_PI + M_PI_2;

CGFloat width = CGRectGetWidth(imageView.frame)/2.0f + 30;
CGFloat height = CGRectGetHeight(imageView.frame)/2.0f +50;
CGPoint centerPoint = CGPointMake(width, height);

float radius = CGRectGetWidth(imageView.frame)/2+10;

clockWiseLayer.path = [UIBezierPath bezierPathWithArcCenter:centerPoint
                                                    radius:radius
                                                startAngle:startAngle
                                                  endAngle:endAngle
                                                 clockwise:YES].CGPath;

clockWiseLayer.fillColor = [UIColor clearColor].CGColor;
clockWiseLayer.strokeColor = [UIColor blueColor].CGColor;
clockWiseLayer.borderColor = [UIColor greenColor].CGColor;
clockWiseLayer.backgroundColor = [UIColor redColor].CGColor;

clockWiseLayer.strokeStart = 0.0f;
clockWiseLayer.strokeEnd = 0.5f;

clockWiseLayer.lineWidth = 2.0f;
clockWiseLayer.borderWidth = 5.0f;

clockWiseLayer.shouldRasterize = NO;
[self.layer addSublayer:clockWiseLayer];

结果如下。

我想要这个蓝色的半圆圈在地球仪的另一边。

它是半圆，但我想要它在另一边，也是 CounterClockWise。

我无法为此设置开始和结束角度，而顺时针:否。

谢谢。

Answer 1

检查坐标文档: http://i.stack.imgur.com/1yJo6.png

与数学中的标准坐标系相比，Y 轴是反转的。

您应该从 1/2*PI(底部 anchor )绘制到 3/2*PI(顶部 anchor )，然后将 strokeStart 设置为 0.0f，将 strokeEnd 设置为 1.0f(这样它会填满整个路径)。

使用 iOS 常量的工作代码:

CGFloat startAngle = M_PI_2;
CGFloat endAngle = startAngle + M_PI;
CGFloat width = CGRectGetWidth(imageView.frame)/2.0f;
CGFloat height = CGRectGetHeight(imageView.frame)/2.0f;
CGPoint centerPoint = CGPointMake(width, height);
float radius = CGRectGetWidth(imageView.frame)/2+10;
CAShapeLayer* clockWiseLayer = [[CAShapeLayer alloc] init];
clockWiseLayer.path = [UIBezierPath bezierPathWithArcCenter:centerPoint
                                                     radius:radius
                                                 startAngle:startAngle
                                                   endAngle:endAngle
                                                  clockwise:YES].CGPath;

clockWiseLayer.fillColor = [UIColor clearColor].CGColor;
clockWiseLayer.strokeColor = [UIColor blueColor].CGColor;
clockWiseLayer.borderColor = [UIColor greenColor].CGColor;
clockWiseLayer.backgroundColor = [UIColor redColor].CGColor;

clockWiseLayer.strokeStart = 0.0f;
clockWiseLayer.strokeEnd = 1.0f;

clockWiseLayer.lineWidth = 2.0f;
clockWiseLayer.borderWidth = 5.0f;
[self.layer addSublayer:clockWiseLayer];