How can the current displayed frame be determined during an animation?

In iOS, to determine the current displayed frame of an animation, you can use the CADisplayLink class. It allows synchronizing updates with the screen refresh rate and tracking the progress of the animation.

The idea is to create a CADisplayLink that calls a method on each frame, and in this method, calculate the current progress of the animation based on the time.

Example of using CADisplayLink to track the current frame:

var displayLink: CADisplayLink?
var animationStartTime: CFTimeInterval = 0
var animationDuration: CFTimeInterval = 2.0 // duration of the animation in seconds

func startAnimation() {
    animationStartTime = CACurrentMediaTime()
    displayLink = CADisplayLink(target: self, selector: #selector(updateAnimation))
    displayLink?.add(to: .main, forMode: .default)
}

@objc func updateAnimation() {
    let elapsed = CACurrentMediaTime() - animationStartTime
    let progress = min(elapsed / animationDuration, 1.0) // from 0 to 1
    // Here you can update the animation state depending on progress
    print("Current animation progress: \(progress)")
    if progress >= 1.0 {
        displayLink?.invalidate()
        displayLink = nil
    }
}

Thus, progress reflects the current "frame" of the animation in relative time units.