Real time progress/frame observation with new Core Animation engine

[tfmart]

First of all, kudos on shipping the new animation engine! The performance improvements have really been noticeable in some tests I've been doing! 🚀

However, in some cases I need to able to observe the progress or current frame of an animation in real time. In the past, I've been using this helper that uses the display link to capture the current progress/frame of an animation in a frame. These still work on version 4.0+, but only when using the legacy main thread engine. If I attempt to use the newer Core Animation one, the observer helper fails to fetch the realtime animation values.

Has anyone got something similar to work on the new engine? Or could help me point out some possible issues with my code? Here is my helper classes as of now:

CADisplayLink (iOS)

internal class AnimationProgressObserver {
    private var animationView: LottieAnimationView
    internal var onFrameChange: ((CGFloat) -> Void)?
    internal var onProgressChange: ((CGFloat) -> Void)?
    private var lastAnimationProgress: CGFloat = -1
    private var lastAnimationFrame: CGFloat = -1
    
    internal init(animationView: LottieAnimationView, onFrameChange: ((CGFloat) -> Void)? = nil, onProgressChange: ((CGFloat) -> Void)? = nil) {
        self.animationView = animationView
        self.onFrameChange = onFrameChange
        self.onProgressChange = onProgressChange
        let displayLink: CADisplayLink = CADisplayLink(target: self, selector: #selector(displayLinkTick))
        displayLink.add(to: RunLoop.current, forMode: .default)
    }
    
    @objc private func displayLinkTick() {
        if let onFrameChange = onFrameChange,
           lastAnimationFrame != animationView.realtimeAnimationFrame {
            lastAnimationFrame = animationView.realtimeAnimationFrame
            onFrameChange(animationView.realtimeAnimationFrame)
        }
        
        if let onProgressChange = onProgressChange,
           lastAnimationProgress != animationView.realtimeAnimationProgress {
            lastAnimationProgress = animationView.realtimeAnimationProgress
            onProgressChange(animationView.realtimeAnimationProgress)
        }
    }
}

CVDisplayLink (macOS)

class AnimationProgressObserver {
    private weak var animationView: LottieAnimationView?
    internal var onFrameChange: ((CGFloat) -> Void)?
    internal var onProgressChange: ((CGFloat) -> Void)?
    private var lastAnimationProgress: CGFloat = -1
    private var lastAnimationFrame: CGFloat = -1
    private var displayLink: CVDisplayLink?
    
    init(animationView: LottieAnimationView?,
         onFrameChange: ((CGFloat) -> Void)?,
         onProgressChange: ((CGFloat) -> Void)?) {
        self.animationView = animationView
        self.onFrameChange = onFrameChange
        self.onProgressChange = onProgressChange
        
        guard displayLink == nil else { return }
        
        var displayLink: CVDisplayLink?
        CVDisplayLinkCreateWithActiveCGDisplays(&displayLink)
        guard let displayLink = displayLink else { return }
        
        self.displayLink = displayLink
        CVDisplayLinkSetOutputCallback(displayLink, { _, _, _, _, _, userData in
            let observer = Unmanaged<AnimationProgressObserver>.fromOpaque(userData!).takeUnretainedValue()
            observer.tick()
            return kCVReturnSuccess
        }, Unmanaged.passUnretained(self).toOpaque())
        
        CVDisplayLinkStart(displayLink)
    }
    
    deinit {
        stop()
    }
    
    func stop() {
        guard let displayLink = displayLink else { return }
        CVDisplayLinkStop(displayLink)
        self.displayLink = nil
    }
    
    private func tick() {
        DispatchQueue.main.async {
            guard let animationView = self.animationView else { return }
            let progress = animationView.realtimeAnimationProgress
            let frame = animationView.realtimeAnimationFrame
            self.onProgressChange?(progress)
            self.onFrameChange?(frame)
        }
        
    }
}