如何为CATextLayer的字符串设置动画? [英] How to animate the string of a CATextLayer?

问题描述

我目前正在使用AVMutableComposition在视频中叠加一些文本，我想根据某个时间间隔重复更改字符串.我正在尝试使用核心动画"来实现这一目标；但是，string属性似乎无法设置动画.还有其他方法可以实现目标吗?谢谢.

I am currently overlaying some text in a video using the AVMutableComposition, I would like to change the string repeatedly based on some time interval. I am trying to use the Core Animation to achieve this; however, the string property does not seem to be animatable. Is there any other way to achieve the goal? Thanks.

代码(不起作用):

func getSubtitlesAnimation(withFrames frames: [String], duration: CFTimeInterval)->CAKeyframeAnimation {
    let animation = CAKeyframeAnimation(keyPath:"string")
    animation.calculationMode = kCAAnimationDiscrete
    animation.duration = duration
    animation.values = frames
    animation.keyTimes = [0,0.5,1]
    animation.repeatCount = Float(frames.count)
    animation.isRemovedOnCompletion = false
    animation.fillMode = kCAFillModeForwards
    animation.beginTime = AVCoreAnimationBeginTimeAtZero
    return animation
}

推荐答案

Swift 5解决方案:

Solution for Swift 5:

喜欢@ agibson007的答案

like the answer from @agibson007

在0.25的时间内进行了优化，不可能更快. (存在褪色/闪烁的问题)

optimized for a duration of 0.25, faster wasn´t possible. (problems with fading / flicker)

func animateText(subtitles:[String],duration:Double,animationSpacing:Double,frame:CGRect,targetLayer:CALayer){
        var currentTime : Double = 0
        for x in 0..<subtitles.count{
            let textLayer = CATextLayer()
            textLayer.frame = frame
            textLayer.string = subtitles[x]
            textLayer.font = UIFont.systemFont(ofSize: 20)
            textLayer.foregroundColor = UIColor.black.cgColor
            textLayer.fontSize = 40.0
            textLayer.alignmentMode = .center
            let anim = getSubtitlesAnimation(duration: duration, startTime: currentTime)
            textLayer.add(anim, forKey: "opacityLayer\(x)")
            targetLayer.addSublayer(textLayer)
            currentTime += duration + animationSpacing
        }
    }

    func getSubtitlesAnimation(duration: CFTimeInterval,startTime:Double)->CAKeyframeAnimation {
        let animation = CAKeyframeAnimation(keyPath:"opacity")
        animation.duration = duration
        animation.calculationMode = .discrete
        animation.values = [0,1,1,0,0]
        animation.keyTimes = [0,0.00000001,0.999,0.999995,1]
        animation.isRemovedOnCompletion = false
        animation.fillMode = .both
        animation.beginTime = AVCoreAnimationBeginTimeAtZero + startTime // CACurrentMediaTime() <- NO AV Foundation
        return animation
    }

    let steps = 0.25
    let duration = 8.0
    let textFrame = CGRect( x: (videoSize.width / 2) - (90 / 2) , y: videoSize.height * 0.2, width: 90, height: 50)

    var subtitles:[String] = []
    for i in 0...Int(duration / steps) {
        let time = i > 0 ? steps * Double(i) : Double(i)
        subtitles.append(String(format: "%0.1f", time) )
    }

    animateText(subtitles: subtitles, duration: steps, animationSpacing: 0, frame: textFrame, targetLayer: layer)

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