The Easing library is a comprehensive set of easing functions, useful for interactive transitions and other time-based calculations.

Features

• Unified set of easing functions
• Easy-to-use 'swifty' API to invoke calculations
• Interpolation shorthands for commonly used types like CGPoint, CGSize, CGTransform, UIColor and UIBezierPath
• Arbitrary cubic bezier based easings (see .cubicBezier(...))
• Emulate default easings from iOS (see .caEaseIn, .caEaseOut, .caEaseInEaseOut)
• Interactive demo app
• Supports iOS 12.0+ / Mac OS X 10.13+ / tvOS 12.0+ / watchOS 4.0+ / visionOS 1.0+

Usage

Basic

let startValue = 20.0
let endValue = 60.0
let progress = 0.5  // Assume a progress variable that ranges from 0 to 1

let valueAtProgress = Easing.cubicEaseIn.calculate(
    d1: startValue,
    d2: endValue,
    g: progress
)

Real world example

Imagine an interaction with a UIScrollView where its header is fully visible when the content offset is zero and fades out completely as the content offset exceeds 100 points. You can express this behavior with the following code in your scrollViewDidScroll method:

let minOffset = 0.0
let alphaForMinOffset = 0.0
let maxOffset = 100.0
let alphaForMaxOffset = 1.0
let offset = scrollView.contentOffset.y

headerView.alpha = Easing.quadraticEaseInOut.calculate(
    g1: minOffset,
    d1: alphaForMinOffset,
    g2: maxOffset,
    d2: alphaForMaxOffset,
    g: offset
)

Interpolatable

let startTransform = CGAffineTransform.identity
let endTransform = CGAffineTransform(scaleX: 2, y: 2)
let progress = 0.5  // Assume a progress variable that ranges from 0 to 1

view.transform = startTransform.interpolate(to: endTransform,
                                      progress: progress,
                                        easing: .linear)

Reference

Easing	Curve
.linear
.smoothStep
.smootherStep
.quadraticEaseIn
.quadraticEaseOut
.quadraticEaseInOut
.cubicEaseIn
.cubicEaseOut
.cubicEaseInOut
.quarticEaseIn
.quarticEaseOut
.quarticEaseInOut
.quinticEaseIn
.quinticEaseOut
.quinticEaseInOut
.sineEaseIn
.sineEaseOut
.sineEaseInOut
.circularEaseIn
.circularEaseOut
.circularEaseInOut
.exponentialEaseIn
.exponentialEaseOut
.exponentialEaseInOut
.elasticEaseIn
.elasticEaseOut
.elasticEaseInOut
.backEaseIn
.backEaseOut
.backEaseInOut
.bounceEaseIn
.bounceEaseOut
.bounceEaseInOut
.caEaseIn
.caEaseOut
.caEaseInEaseOut
.cubicBezier(0.11, 0.87, 0.21, -0.88)

Demo app

In the repo, you will find an interactive demo iOS app to experiment with different easings and discover the most suitable one for your needs.

Integration

Use Swift Package Manager and add dependency to Package.swift file.

  dependencies: [
    .package(url: "https://github.com/psharanda/Easing.git", .upToNextMajor(from: "3.0.0"))
  ]

Alternatively, in Xcode select File > Add Package Dependencies… and add Easing repository URL:

https://github.com/psharanda/Easing.git

References

The main set of easing functions is a Swift port of https://github.com/warrenm/AHEasing and https://github.com/ai/easings.net

CubicBezierInterpolator is a Swift port of nsSMILKeySpline code from Mozilla https://github.com/mozilla-services/services-central-legacy/blob/master/content/smil/nsSMILKeySpline.cpp

Contributing

We welcome contributions! If you find a bug, have a feature request, or want to contribute code, please open an issue or submit a pull request.

License

Easing is available under the MIT license. See the LICENSE file for more info.