如何避免旋转动画在 2π 边界处跳跃？

Question

我正在使用 CAKeyframeAnimation 沿 CGPath 为箭头设置动画。箭头跟随路径，atan2 'flip' 从 0 到 2π 的输出除外，反之亦然。在这种情况下，箭头会在继续之前完成完整的 360° 旋转。

有什么方法可以计算我的 CAKeyframeAnimation 的值，以便箭头始终旋转最小的量以到达它要去的地方？

        let turnAnimation = CAKeyframeAnimation(keyPath: "transform.rotation")
        turnAnimation.duration = 5

        var values = [CGFloat]()
        for i in 0..<points.count - 1 {

            let point1 = points[i]
            let point2 = points[i + 1]
            let delta = point2 - point1
            let value = atan2(delta.y, delta.x)

            values.append(value)
        }

        turnAnimation.values = values
        turnAnimation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
        turnAnimation.repeatCount = Float.greatestFiniteMagnitude
        arrowPointLayer.transform = CATransform3DMakeRotation(values.first!, 0, 0, 1)
        arrowPointLayer.add(turnAnimation, forKey: "rotateArrow")

编辑：根据答案更新，但仍不能正常工作：

let turnAnimation = CAKeyframeAnimation(keyPath: "transform.rotation")
        turnAnimation.duration = 5

        var rawValues = [CGFloat]()
        var values = [CGFloat]()
        for i in 0..<points.count - 1 {

            let point1 = points[i]
            let point2 = points[i + 1]
            let delta = point2 - point1
            let rawValue = atan2(delta.y, delta.x)

            var value: CGFloat

            if i == 0 {
                value = 0 // we will apply this value from rawValues
            } else {
                let lastValue = rawValues.last!
                value = rawValue - lastValue
            }

            if value < 0 {
                value = .pi * 2 + value
            }

            rawValues.append(rawValue)

            values.append(value)
        }

        for (i, p) in values.enumerated() {
            print("\(rawValues[i]): \(p)")
        }

        turnAnimation.values = values
        turnAnimation.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
        turnAnimation.repeatCount = Float.greatestFiniteMagnitude
        turnAnimation.isAdditive = true

        arrowPointLayer.transform = CATransform3DMakeRotation(rawValues.first!, 0, 0, 1)
        arrowPointLayer.add(turnAnimation, forKey: "rotateArrow")

Answer 1

不要将values 设为绝对旋转值列表，而是将其设为旋转差异 列表并将动画的isAdditive 设置为true。这样一来，你就在告诉箭头转向哪个方向以及转向多少。

我是这样测试的（在我的测试中，v 只是我界面中的一些视图）：

let turnAnimation = CAKeyframeAnimation(keyPath: "transform.rotation")
turnAnimation.duration = 5
let values : [CGFloat] = [0,2,-1,2,-1,3,-3]
turnAnimation.values = values
turnAnimation.timingFunction = 
    CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
turnAnimation.isAdditive = true
self.v.layer.add(turnAnimation, forKey: "rotateArrow")

视图的行为完全符合我的预期。