Advance

An animation library for iOS, tvOS, and macOS that uses physics-based animations (including springs) to power interactions that move and respond realistically.

let view = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))

// Springs animate changes to a value
let spring = Spring(initialValue: view.center)

// The `onChange` closure will be called every time the spring updates
spring.onChange = { [view] newCenter in
    view.center = newCenter
}

/// The view's center will realistically animate to the new target value.
spring.target = CGPoint(x: 300, y: 200)

Installation

There are several ways to integrate Advance into your project.

Manually: add Advance.xcodeproj to your project, then add Advance-{iOS|macOS|tvOS}.framework as an "Embedded Binary" to your application target (under General in target settings). From there, add import Advance to your code and you're good to go.
Carthage: add github "timdonnelly/Advance" to your Cartfile.
CocoaPods: add pod 'Advance' to your Podfile.
Swift Package Manager: add a dependency to your Project.swift: .package(url: "http://github.com/timdonnelly/Advance", from: "3.0.0")

Requirements

iOS 10+, tvOS 10+, or macOS 10.12+
Swift 5.0 (Xcode 10.2 or higher)

Usage

API documentation is available here.

Advance animations are applied on every frame (using CADisplayLink on iOS/tvOS, and CVDisplayLink on macOS), allowing for fine-grained control at any time.

`Spring`

Spring instances animate changes to a value over time, using spring physics.

let spring = Spring(initialValue: 0.0)
spring.onChange = { [view] newAlpha in 
    view.alpha = newAlpha 
}

// Off it goes!
spring.target = 0.5

Configuring a spring

/// Spring values can be adjusted at any time.
spring.tension = 30.0 /// The strength of the spring
spring.damping = 2.0 /// The resistance (drag) that the spring encounters
spring.threshold = 0.1 /// The maximum delta between the current value and the spring's target (for each component) for which the simulation can enter a converged state.

/// Update the simulation state at any time.
spring.velocity = 6.5
spring.value = 0.2

/// Sets the spring's target and the current simulation value, and removes all velocity. This causes the spring to converge at the given value.
spring.reset(to: 0.5)

`Animator`

Animator allows for more flexibility in the types of animation that can be performed, but gives up some convenience in order to do so. Specifically, animators allow for any type of animation or simulation to be performed for a single value.

let view = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))

/// Animators coordinate animations to drive changes to a value.
let sizeAnimator = Animator(initialValue: view.bounds.size)

sizeAnimator.onChange = { [view] newSize in
    view.bounds.size = newSize
}

/// A simple timed animation
sizeAnimator.animate(to: CGSize(width: 123, height: 456), duration: 0.25, timingFunction: .easeInOut)

/// Some time in the future (before the previous timed animation was complete)...

/// Spring physics will move the view's size to the new value, maintaining the velocity from the timed animation.
sizeAnimator.simulate(using: SpringFunction(target: CGSize(width: 300, height: 300)))

/// Some time in the future (before the previous spring animation was complete)...

/// The value will keep the same velocity that it had from the preceeding spring
/// animation, and a decay function will slowly bring movement to a stop.
sizeAnimator.simulate(using: DecayFunction(drag: 2.0))

Animators support two fundamentally different types of animations: timed and simulated.

Timed animations

Timed animations are, well, timed: they have a fixed duration, and they animate to a final value in a predictable manner.

animator.animate(to: CGSize(width: 123, height: 456), duration: 0.25, timingFunction: .easeInOut)

TimingFunction described the pacing of a timed animation.

TimingFunction comes with a standard set of functions:

TimingFunction.linear // No easing
TimingFunction.easeIn
TimingFunction.easeOut
TimingFunction.easeInOut
TimingFunction.swiftOut // Similar to Material Design's default curve

Custom timing functions can be expressed as unit beziers (described here).

let customTimingFunction = TimingFunction(x1: 0.1, y1: 0.2, x2: 0.6, y2: 0.0)

Simulated animations

Simulated animations use a simulation function to power a physics-based transition. Simulation functions are types conforming to the SimulationFunction protocol.

Simulated animations may be started using two different methods:

// Begins animating with the custom simulation function, maintaining the previous velocity of the animator.
animator.simulate(using: MyCustomFunction())

// or...

// Begins animating with the custom simulation function, imparting the specified velocity into the simulation.
animator.simulate(using: DecayFunction(), initialVelocity: dragGestureRecognizer.velocity(in: view))

Animating Custom Types

Values conforming to the VectorConvertible protocol can be animated by Advance. Conforming types can be converted to and from a Vector implementation.

public protocol VectorConvertible: Equatable, Interpolatable {
    associatedtype VectorType: SIMD where VectorType.Scalar == Double
    init(vector: VectorType)
    var vector: VectorType { get }
}

The library adds conformance for many common types through extensions.

Contributing

If you encounter any issues or surprises, please open an issue.

For suggestions or new features, please consider opening a PR with a functional implementation. Issues may be used if you aren't sure how to implement the change, but working code is typically easier to evaluate.

License

This project is released under the BSD 2-clause license.

timdonnelly/Advance