Animate with Ease

animate-with-ease.swift

enum AnimationEase {
    case linear
    case easeIn
    case easeInOut
    case easeOut
}
func animate(for duration: CGFloat, ease: AnimationEase = .linear, loop: @escaping (CGFloat) -> (), done: @escaping () -> ()) {
    let startTime = Date()
    RunLoop.current.add(Timer(timeInterval: 1.0 / Double(UIScreen.main.maximumFramesPerSecond), repeats: true, block: { t in
        let elapsedTime = CGFloat(-startTime.timeIntervalSinceNow)
        let fraction = min(elapsedTime / duration, 1.0)
        var easeFraction = fraction
        switch ease {
        case .linear: break
        case .easeIn: easeFraction = cos(fraction * .pi / 2 - .pi) + 1
        case .easeInOut: easeFraction = cos(fraction * .pi - .pi) / 2 + 0.5
        case .easeOut: easeFraction = cos(fraction * .pi / 2 - .pi / 2)
        }
        loop(easeFraction)
        if fraction == 1.0 {
            done()
            t.invalidate()
        }
    }), forMode: .common)
}