Introducing Anima, an Animation Framework for iOS, tvOS, and macOS

I created an open source animation framework for iOS, tvOS, and macOS. It can animate properties using spring, easing and decay animations.

Github: Anima
Documentation: Online

Animatable Properties

Any type conforming to AnimatableProperty can be animated by Anima.

By default, lots of types already conform to it:

  • Float
  • Double
  • CGFloat
  • CGPoint
  • CGSize
  • CGRect
  • CGColor/NSColor/UIColor
  • CATransform3D / CGAffineTransform
  • Arrays with AnimatableProperty values
  • … and many more.


There are two ways you can can create animations: block-based and property-based.

Block-Based Animations

Block-based animation lets you easily animate properties of objects conforming to AnimatablePropertyProvider.

Many objects already conform to it and provide animatable properties:

  • macOS: NSView, NSWindow, NSTextField, NSImageView and many more.
  • iOS: UIView, UILabel, UIImageView and many more.
  • Shared: NSLayoutConstraint and CALayer

The properties can can be accessed via the object's animator. To animate them change their values inside an animation block using Anima.animate(…). For example:

Anima.animate(withSpring: .bouncy) {
    view.animator.frame = newFrame
    view.animator.backgroundColor = .systemBlue
    textField.animator.fontSize = 20

To stop the animation of a property and to update it immediately, change it's value outside an animation block. For example:

view.animator.backgroundColor = .systemRed

Spring Animation

A spring based animation for fluid animations.

You provide a Spring which describes the spring configuration. Spring offers many predefined configurations like bouncy, smooth, snappy or Spring(duration: CGFloat, bouncy: CGFloat)).

Anima.animate(withSpring: .bouncy) {
    view.animator.frame = newFrame
    view.animator.backgroundColor = .systemBlue

When changing the value of a property that is currently animated, the animation’s velocity is preserved to provide fluid animations. That's why spring animation is the recommended animation for a responsive and interactive UI.

You can provide a gesture velocity for spring animations. This can be used to "inject" the velocity of a gesture recognizer (when the gesture ends) into the animations. If you apply a velocity of type CGPoint it's used for animating properties of type GGPoint and CGRect.

let velocity = panGestureRecognizer.velocity(in: view)

Anima.animate(withSpring: .snappy, gestureVelocity: velocity) {
    view.animator.frame.origin = CGPoint(x: 200, y: 200)

Easing Animation

An easing based animation.

You provide a TimingFunction which describes the easing of the animation (e.g. easeIn, easeInOut or linear) and a duration.

Anima.animate(withEasing: .easeIn, duration: 3.0) {
    view.animator.frame = newFrame
    view.animator.backgroundColor = .systemBlue

Decay Animation

Performs animations with a decaying acceleration.

You either provide values and the animation will animate the properties to the values with a decelerating acceleration.

Anima.animate(withDecay: .value) {
    view.animator.frame = newFrame
    view.animator.backgroundColor = .systemBlue

Or you provide velocity values. The properties will increase or decrease depending on the velocity values and will slow to a stop. This essentially provides the same "decaying" that UIScrollView does when you drag and let go. The animation is seeded with velocity, and that velocity decays over time.

Anima.animate(withDecay: .velocity) {
    // The origin's y value will increase 200 points. (e.g. if the origin`s y value is 250 it will move to 450)
    view.animator.frame.origin.y = 200

Property-Based Animations

While the block-based API is often most convenient, you may want to animate an object that doesn't provide animatable properties. Or, you may want the flexibility of getting the intermediate values of an animation and driving an animation yourself.

To create an property-based animation you provide an initial value, target value and valueChanged, a block that gets called whenever the animation's current value changes.

Spring Animation

let value = CGPoint(x: 0, y: 0)
let target = CGPoint(x: 100, y: 100)

let springAnimation = SpringAnimation(spring: .bouncy, value: value, target: target)
springAnimation.valueChanged = { newValue in
    view.frame.origin = newValue

Easing Animation

let easingAnimation = EasingAnimation(timingFunction: .easeIn, duration: 2.0, value: value, target: target)
easingAnimation.valueChanged = { newValue in
    view.frame.origin = newValue

Decay Animation

// Decay animation with target
let decayAnimation = DecayAnimation(value: value, target: target)
decayAnimation.valueChanged = { newValue in
    view.frame.origin = newValue

// Decay animation with velocity
let decayVelocityAnimation = DecayAnimation(value: value, velocity: velocity)


To create your own animations overwrite this PropertyAnimation. The class isn't animating and you have to provide your own animation logic.



All animations in Anima conform to CAKeyframeAnimationEmittable and provide a CAKeyframeAnimation via keyframeAnimation that mirrors the animation. The duration, keyframes and everything else is automatically calculated. The only difference is valueChanged and completion cannot be used, and you must specify a keypath to animate.

For example:

let springAnimation = SpringAnimation<CGRect>(spring: .bouncy, value: frame, target: targetFrame)

let keyframeAnimation = springAnimation.keyframeAnimation()
keyframeAnimation.keyPath = "frame"

layer.add(keyframeAnimation, forKey: "MyAnimation")

Note: If you remove or interrupt the animation and you want it to stay in place on screen, much like all other Core Animation animations, you'll need to grab the value from the layer's presentationLayer and apply that to the layer (as well as worry about fillMode).


Rubberbanding is the act of making values appear to be on a rubberband (they stretch and slip based on interaction). UIScrollView does this when you're pulling past the contentSize and by using the rubberband functions in Motion you can re-create this interaction for yourself.

 bounds.origin.x = rubberband(bounds.origin.x - translation.x, boundsSize: bounds.size.width, contentSize: contentSize.width)