Is there an equivalent of FastOutSlowInInterpolator for iOS?

Question

Is there an equivalent of FastOutSlowInInterpolator for iOS? I've recently got my hands on AndroidX and really like this interpolator. I've found the source code for it too but have no idea how to convert it to iOS implementation.

Answer 1

If you are using UIViewPropertyAnimator the curve that you need is .easeInOut, and you can pass it as curve parameter when you create your animator:

let animator = UIViewPropertyAnimator(duration: 0.4, curve: .easeInOut) {
    // Animations
}

If you are not happy with this system curve, you can follow this answer and use this handy website to replicate FastOutSlowInInterpolator's control points.

As FastOutSlowInInterpolator documentation states:

Interpolator corresponding to fast_out_slow_in. Uses a lookup table for the Bezier curve from (0,0) to (1,1) with control points: P0 (0, 0) P1 (0.4, 0) P2 (0.2, 1.0) P3 (1.0, 1.0)

So, in your particular case you are looking for something like this:

let timingParameters = UICubicTimingParameters(
    controlPoint1: CGPoint(x: 0.4, y: 0),
    controlPoint2: CGPoint(x: 0.2, y: 1)
)
let animator = UIViewPropertyAnimator(duration: 0.4, timingParameters: timingParameters)

or this:

let animator = UIViewPropertyAnimator(
    duration: 0.4,
    controlPoint1: CGPoint(x: 0.4, y: 0),
    controlPoint2: CGPoint(x: 0.2, y: 1)
) {
    // Animations
}