CAKeyframeAnimation逆时针

Question

我想要沿bezierPath逆时针方向设置动画。

目前，下面的代码只允许我按顺时针方向操作。

        let arrowHead = UIImageView()
        arrowHead.image = UIImage(named: "arrowHead.png")
        arrowHead.frame = CGRect(x: 55, y: 300, width: 12, height: 12)


        let ovalPath = UIBezierPath(ovalInRect: CGRectMake(50, 240, 320, 240))
        let ovalShapeLayer = CAShapeLayer()
        ovalShapeLayer.fillColor = UIColor.clearColor().CGColor
        ovalShapeLayer.strokeColor = UIColor.lightGrayColor().CGColor
        ovalShapeLayer.lineWidth = 1.5
        ovalShapeLayer.path = ovalPath.CGPath


        self.view.layer.addSublayer(ovalShapeLayer)

        let myKeyFrameAnimation = CAKeyframeAnimation(keyPath: "position")
        myKeyFrameAnimation.path = ovalPath.CGPath

        myKeyFrameAnimation.rotationMode = kCAAnimationRotateAuto
        myKeyFrameAnimation.repeatCount = Float.infinity
        myKeyFrameAnimation.duration = 6.0

        // add the animation
        arrowHead.layer.addAnimation(myKeyFrameAnimation, forKey: "animate position along path")
        self.view.addSubview(arrowHead)

有什么想法吗？

Answer 1

好的，明白了。

myKeyFrameAnimation.speed = -1

非常简单..。

Answer 2

另一种解决方案是使用bezierPathWithArcCenter...作为文档记录的here，它允许您指定圆的方向。使用-M_PI_2作为起点角度，3 * M_PI_2作为终点角度，将在顶部产生一个圆的起点和终点。