贝塞尔曲线

最近在做人脸识别，相机界面需要中间一个圆为透明，圆外部分半透明，用贝塞尔曲线实现如下：

//画周围白色半透明区域
CAShapeLayer *pShapeLayer = [CAShapeLayer layer];
    pShapeLayer.fillColor = [UIColor colorWithWhite:1 alpha:0.6].CGColor;
    pShapeLayer.frame = overView.frame;
    [overView.layer addSublayer:pShapeLayer];
    //圆弧
    UIBezierPath *pPath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(HALFABOUTUISCREEN_WIDTH, HALFABOUTUISCREEN_HIGHT - kCircleCenterY)
                                        radius:self.bounds.size.width / 2.0 + self.progressStrokeWidth / 2.0 startAngle:0.0 endAngle:M_PI * 2 clockwise:YES];
    pShapeLayer.path = pPath.CGPath;
    //矩形
    UIBezierPath *pOtherPath = [UIBezierPath bezierPathWithRect:
                                CGRectMake(0, 0, ScreenWidth, ScreenHeight)];
    pShapeLayer.path = pOtherPath.CGPath;

    [pOtherPath appendPath:pPath];
    pShapeLayer.path = pOtherPath.CGPath;
    //重点
    pShapeLayer.fillRule = kCAFillRuleEvenOdd;

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