Latest 1.1.2
License MIT
Platforms ios 9.0, requires ARC
Frameworks UIKit

Total Downloads
CI Status

A super-flexible tweening library for iOS in Swift inspired by GSAP.


  • iOS 9.0+
  • Swift 3.0+
  • Xcode 8+


The following docs are meant to give a general overview of interacting with the library and the various functionality currently supported. For a better, more in-depth demonstration on working with this library, make sure to review the code provided in the example project. To run the example project, clone the repo, open the Kinetic.xcworkspace and run the Kinetic-Example project.


  • CocoaPods: add pod "Kinetic" to your Podfile
  • Carthage: add github "u10int/Kinetic" "master" to your Cartfile


  • Quickly setup animations in a syntax inspired by TweenMax, TimelineMax and the awesome GSAP
  • Start, stop, pause and resume any animation during runtime
  • Easings and springs for more realistic and interesting animations
  • Chaining methods for concise code
  • Support for animating from, animating to, or animating from and to specific values (to:, from:)
  • Animate multiple objects sequentially, in parallel or staggered in a single animation group
  • Advanced animations using timelines to insert gaps, callbacks and more during an animation
  • Support for animating any NSObject property on your custom objects or any tweenable value


  • Improve and cleanup API
  • Support for animating elements along a UIBezierPath
  • Support for animating SVG drawings
  • Support for animating text and characters



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

Basic Examples

Animating multiple properties of an UIView or CALayer can be done in a single line of code:

let square = UIView()
square.frame = CGRect(x: 50, y: 50, width: 50, height: 50)
square.backgroundColor = UIColor.redColor()

// move 250pt to the right and set the height to 100pt for 0.5 seconds
Kinetic.animate(square).to(X(250), Size(height: 100)).duration(0.5).ease(Quartic.easeInOut).play()

Alternatively, you can setup a tween on a UIView or CALayer instance by using the tween() properly, which is an extension provided by Kinetic:

square.tween().to(X(250), Size(height: 100)).duration(0.5).ease(Quartic.easeInOut).play()

Basic Tween

Animating the same properties on multiple objects is just as quick and easy:

let greenSquare = UIView()
greenSquare.frame = CGRect(x: 0, y: 50, width: 100, height: 100)
greenSquare.backgroundColor = UIColor (red: 0.0557, green: 0.7144, blue: 0.0677, alpha: 1.0)

let blueSquare = UIView()
blueSquare.frame = CGRect(x: 0, y: 50, width: 100, height: 100)
blueSquare.backgroundColor = UIColor (red: 0.0, green: 0.6126, blue: 0.9743, alpha: 1.0)

let orangeSquare = UIView()
orangeSquare.frame = CGRect(x: 0, y: 160, width: 100, height: 100)
orangeSquare.backgroundColor = .orange

let timeline = Kinetic.animateAll([greenSquare, blueSquare, orangeSquare]).to(Rotation(y: CGFloat(Double.pi / 2))).duration(1)
timeline.ease(Sine.easeInOut).perspective(1 / -1000).yoyo().repeatCount(3)

And similar to individual tween targets above, you can use the tween() method on an array of Tweenable objects which will setup a tween but instead return an instance of Timeline:

let timeline = [greenSquare, blueSquare, orangeSquare].tween().to(Rotation(y: CGFloat(Double.pi / 2))).duration(1)

Grouped Tween

Review the example project for more in-depth and complex animation examples using Kinetic.

Animatable Properties

Kinetic has support for animating most visible properties on UIView and CALayer already built-in, but you can also animating any custom key-value property on NSObject:


Property Description
Position(_ position: CGPoint) Animates the target’s origin/position using the specified CGPoint value
Position(_ x: CGFloat, _ y: CGFloat) Animates the target’s origin/position using the specified x and y values
X(x: CGFloat) Animates the target’s origin.x or position.x value
Y(y: CGFloat) Animates the target’s origin.y or position.y value
Center(_ center: CGPoint) Animates the target’s center position using the specified CGPoint value
Center(_ x:CGFloat, _ y: CGFloat) Animates the target’s center position using the specified x and y values
Center(x: CGFloat) Animates the target’s center.x value
Center(y: CGFloat) Animates the target’s center.y value
Shift(_ offset: CGPoint) Shifts the frame’s current origin by the specified point’s x and y values as distances (similar to translate but changes the object’s origin value instead of using transform).
Shift(_ x: CGFloat, _ y: CGFloat) Shifts the frame’s current origin by the specified x and y distances (similar to translate but changes the object’s origin value instead of using transform).
Shift(x: CGFloat) Shifts the target’s origin.x position by the specified distance relative to its current position. Negative values will move the target to the left.
Shift(y: CGFloat) Shifts the target’s origin.y position by the specified distance relative to its current position. Negative values will move the target up.


Property Description
Size(_ size: CGSize) Animates the target’s size using the specified CGSize value
Size(_ width: CGFloat, _ height: CGFloat) Animates the target’s size using the specified width and height values
Size(width: CGFloat) Animates the target’s size.width value
Size(height: CGFloat) Animates the target’s size.height value


Property Description
Translation(_ offset: CGPoint) Shifts the frame’s position by the specified point’s x and y values as distances using the layer’s transform property
Translation(_ x: CGFloat, _ y: CGFloat) Shifts the frame’s position by the specified x and y distances using the layer’s transform property
Scale(_ value: CGFloat) Animates the target’s scale by applying the specified scale value to all 3 axes
Scale(x: CGFloat, y: CGFloat, z: CGFloat) Animates the target’s scale using specific scale values for each axis
Rotation(_ value: CGFloat) Animates the rotation of the object two-dimensionally in the z axes to the specified angle
Rotation(x: CGFloat) Animates the rotation of the object in the x axes (for three-dimensional rotation) to the specified angle
Rotation(y: CGFloat) Animates the rotation of the object in the y axes (for three-dimensional rotation) to the specified angle


Property Description
BackgroundColor(_ color: UIColor) Animates the background color of the view or layer to the specified color value
BorderColor(_ color: UIColor) Animates the border color of the view or layer to the specified color value
FillColor(_ color: UIColor) Animates the fill color of the view or layer to the specified color value, typically used on CAShapeLayer instances
StrokeColor(_ color: UIColor) Animates the stroke color of the view or layer to the specified color value, typically used on CAShapeLayer instances


Property Description
Path(_ path: Path) Animates the target’s progress along the specified path
StrokeStart(_ value: CGFloat) Animates the path’s start position
StrokeEnd(_ value: CGFloat) Animates the path’s end position


Property Description
Frame(_ value)
Alpha(_ value: CGFloat) Animates the object’s opacity to the specified value (from 0 to 1.0)
CornerRadius(_ value: CGFloat) Animates the corner radius of the view or layer to the specified value
KeyPath(_ key: String, _ value: Interpolatable) Animates a custom property on an NSObject instance for the specified key path. The value must be a valid Interpolatable type.

The animation properties you provide with your tweens use a very Swift-like syntax where you specify the starting or ending values as parameters to the property you wish to animate. For example, to animate a view’s origin.x from its current position to 100.0 you would use X(100). However, if you just wanted to shift the view from its current location 100pt to the right, you would use Shift(x: 100) instead, which specifies the distance to move the view in just the x axis.


The following are the primary classes used within the library along with their role:

Class Description
Kinetic Central class providing convenience static methods for creating tweens, timelines and removing them from their targets.
Tween Primary class used for performing animations on a single Tweenable target for one or more animatable properties.
Timeline Used for combining multiple tweens into a single group with support for controlling a single tween’s position relative to the overall animation’s duration.
Animation Base class for Tween and Timeline that provides core animation functionality. Is not tied to a specific or series of Tweenable targets like Tween and Timeline are and thus does not perform any value updates automatically during the animation’s duration.
Easing Common easing properties for animations.
Spring Basic spring for physics-based animations.

Interpolatable Values

Underlying each tween instance is a series of values conforming to the Interpolatable protocol, which most common value-types used throughout UIKit already adopt (e.g. CGFloat, CGPoint, UIColor, etc). If you just need to perform a basic value-based interpolation on a property value, you can use an instance of Interpolator instead of the full-featured Tween and/or Timeline classes. This if useful if you have a custom object that is not a subclass of UIView or CALayer and that cannot use the KeyPath() property since it isn’t a subclass of NSObject.

For instance, if you just want to interpolate a value of 100.0 to 500.0 with a specific timing function offered by Kinetic, just use the interpolator(to:duration:function:apply:) method on your starting value:

(100.0.interpolator(to: 500.0, duration: 1.0, function: Easing.type(Quadratic.easeInOut)) { (value) in

When using an interpolator directly, you are responsible for updating the values on the respective instances. Also, this method does not support any of the features available with Tween or Timeline.

Controlling Tweens

Once you have an instance of a Tween using Kinetic.animate: or Timeline using Kinetic.animateAll:, controlling your animation during playback is extremely simple.

You can configure your tween before playback to define its delay, easing or spring, repeat count, or repeat forever:

// sets the initial state of the animation before playback, where `...` is a series of `Property` instances

// sets the final state of the animation when playback completes, where `...` is a series of `Property` instances

// total duration of the animation, in seconds, not including any delay value

// wait 2 seconds before starting the animation

// set the easing to use for the animation, which will be used for all properties in the tween

// configure the tween to use a spring animation, which will be used instead of any easing previously set
tween.spring(tension: 100, friction: 12)

// tell the tween to repeat 4 additional times, meaning it will play a total of 5 times

// set a delay of 0.5 seconds between repeats

// tell the tween to repeat forever until stopped using stop() or pause()

// reverses the direction of playback each time the tween is repeated
// if the tween is configured to repeat 4 times, then the animation will play with the pattern: forward, reversed, forward, reversed, forward.

// set the transform perspective for the tween's associated object
// this is only used for three-dimensional CALayer transformation
tween.perspective(1 / -1000)

Once you’ve configured your tween and started its playback using play(), you can stop, pause, resume, seek, reverse, or restart a tween at any time:

// plays the tween from the beginning

// stops the tween at the current position

// resumes playback from the tween's current position

// reverses playback direction toward the beginning

// returns playback direction to the normal direction

// restarts the tween from the beginning

// jump to 0.5 seconds into the tween

// immediately stop and remove the tween from the object

// get the current progress of the tween from 0 (start) to 1 (end); doesn't account for repeats (a single animation cycle)

// move the animation's playhead progress from 0 (start) to 1 (end) excluding repeats and repeatDelays (a single animation cycle)
tween.setProgress(progress: Float)

// get the current progress of the tween from 0 (start) to 1 (end) including repeats and repeatDelays

// move the animation's playhead progress from 0 (start) to 1 (end) including repeats and repeatDelays
tween.setTotalProgress(progress: Float)

// get the total elapsed time of the tween including any repeats and delays

You can also remove multiple tweens of a single object by using the convenience methods provided by the central Kinetic module:


To remove all tweens currently running from all objects, simply call killAll():


Killing and removing a tween is similar to pause() and will stop the animation at its current position without returning the associated object back to its original starting position. The tween will also be disassociated from the object and removed from the tween cache.


You can assign callback blocks for several events during a tween’s playback, including when it starts, when it updates an object’s properties, when it repeats and when it completes. The Tween instance that called the block will be provided as an argument to your block.

The following events are triggered by an Animation instance:

// called when the tween starts animating
tween.on(.started) { (tween) -> Void in
    print("tween started")

// called when the tween's properties are updated during the animation
tween.on(.updated) { (tween) -> Void in
    print("tween updated: time=(tween.elapsed)")

// called each time the tween repeats
// if the tween's playback is reversed, this will be called when the tween's position reaches the beginning
// of the tween, or 0, instead of the end
tween.on(.repeated) { (tween) -> Void in
    print("tween repeated")

// called when the animation is cancelled before it completes
tween.on(.cancelled) { (tween) -> Void in
    print("tween cancelled")

// called when all properties of the tween have finished animating to their final values
tween.on(.completed) { (tween) -> Void in
    print("tween completed")

Custom Properties

Most of the time you’ll be animating UIView and CALayer instances and their visual properties. However, you may also need to animate a different property not supported with Kinetic’s standard property set or a property of a custom object in your project. You can accomplish this using the KeyPath(_ key: String, _ value: Interpolatable) property with a Tween and a custom NSObject subclass that conforms to the KeyPathTweenable protocol:

class CountingObject: NSObject, KeyPathTweenable {
    var value: Float = 0

A good use case for this is to setup a UILabel that animates a value change, such as from 50 to 250. With a Tween instance and the KeyPath() property, this is just as easy as any other animation:

let textLabel = UILabel()
textLabel.font = UIFont.systemFont(ofSize: 40)
textLabel.textColor =
textLabel.frame = CGRect(x: 50, y: 50, width: 200, height: 50)

let testObject = CountingObject()
testObject.value = 50
textLabel.text = "(testObject.value)"

let tween = testObject.tween()
    .to(KeyPath("value", 250.0))

tween.on(.updated) { (animation) in
    self.textLabel.text = "(String(format:"%.1f", self.testObject.value))"
}.on(.completed) { (animation) in

Counting Label

Any custom property can be used as long as it’s a property of an NSObject subclass that conforms to KeyPathTweenable and the property has a numerical value.

An alternative to using the KeyPath() property method for animating custom properties is using an interpolator directly as explained in the Interpolatable Values section above.


A Kinetic Timeline allows you to group multiple Tween instances into a single, easy to control sequence with precise timing management for more complex animations. Without using a Timeline instance, you would have to create multiple Tween instances and manually calculate their delay values to create the exact sequence you want.

Serial Animations

In many cases, you’ll want to perform a serial, or sequential, animation on a single or multiple objects where each tween is performed one after another. For instance, if you want to move a view to the right, then down, and then scale it up by 2 for a duration of 3 seconds, you could do so by creating three Tween instances and offset their delay values by 1 second:




Note that if you change the duration of any of the individual tweens, you also have to be sure to adjust the delay values for the sequence. And trying to pause, restart or reverse the sequence is even more of a challenge. However, by using a Timeline instance you can perform all of these functions easily:

let timeline = Timeline()

Timeline Sequence

The above timeline will perform each tween sequentially for a total duration of 3 seconds since each tween is 1 second in length.

Instead of having each tween play one after another, you can specify a position for one or all of the tweens in your sequence. For example, we want to play the second tween in the above sequence at 1.5 seconds into the timeline instead of immediately after the first one completes:

let timeline = Timeline()
timeline.add(square.tween().to(Y(250)).duration(1).ease(Cubic.easeInOut), position: 1.5)

This change will play the second tween at 1.5 seconds into the animation, and then the last one immediately after it completes at 2.5 seconds. Therefore, our timeline’s new total duration will be 3.5 seconds instead of 3 seconds.

Timeline Sequence

Grouped + Staggered Animations

Using Kinetic.animateAll you can animate the same properties on multiple objects using a single line of code. For example, you have 3 square views you want to scale up and rotate 45 degrees at the same time:

let squares = [greenSquare, blueSquare, redSquare]
let timeline = squares.tween()
                    .to(Scale(2), Rotation(CGFloat(Math.pi / 2.0)))

Timeline Grouped

Using a Timeline also provides you with the ability to stagger multiple animations for more interesting effects. For instance, you may have a column of horizontal bars whose widths you want to animate to their final state. You could do this with a basic Timeline instance and increasingly offset their positions relative to the start time, but there’s an easier way using stagger: on your Timeline instance:

let squares = [greenSquare, blueSquare, redSquare]
let timeline = squares.tween()
                    .to(Size(width: 250))
                    .spring(tension: 100, friction: 12)

In a single line, you can animate each item in squares from their starting width to a width of 200 using a spring, each offset by 0.08 seconds.

Timeline Staggered

The method Kinetic.animateAll: will return an instance of Timeline.

You can also add labels to your timeline to be used for referencing when adding additional tweens or for playback. For example, you may want to include a color change animation for a view in your timeline and want other tweens to take place relative to that position. First create a label at the time you want to reference and then add your tweens relative to or offset from that label:

let resize = square.tween()

let color = square.tween()

timeline.addLabel("colorChange", position: 1.3)
timeline.add(color, relativeToLabel: "colorChange", offset: 0)
timeline.add(resize, relativeToLabel: "colorChange", offset: 0.5)

Time Labels

You can add any number of time labels to a timeline that can then be used as reference points for specific positions along the timeline. Once a label has been set, you can add tweens to the timeline relative to a specific label using an offset value. Negative offset values will insert the tween that number of seconds before the label:

// use a label to store a position reference when the color change still start animating
timeline.addLabel("colorChange", position: 1.3)

// add the color change tween to the timeline relative to our "colorChange" label
let color = square.tween().to(BackgroundColor(
timeline.add(color, relativeToLabel: "colorChange", offset: 0)

// resize the view 1 second after the color change starts
let resize = square.tween().to(Size(150,100)).duration(1).ease(Cubic.easeInOut)
timeline.add(resize, relativeToLabel: "colorChange", offset: 0.5)

// move the view 0.25 seconds before the color change starts
let move = square.tween().to(Position(200,200)).duration(1).ease(Cubic.easeInOut)
timeline.add(move, relativeToLabel: "colorChange", offset: -0.25)

Timeline Labels

Time Callbacks

With timelines you can also insert callback blocks at any time within a timeline’s total duration, which is useful if you want to perform a certain action while the timeline is playing or perform another animation:

timeline.addCallback(Float(idx) * 0.15 + 1.5, block: {

Timeline Callbacks

Controlling Timelines

Timelines support the same methods as tweens for controlling their playback, such as pause(), stop(), resume(), restart(), and seek(). However, timelines also come with a few more since they support inserting labels at specific times. You can stop at or start playing from a specific label you have previously set on a timeline using goToAndPlay() and goToAndStop():

timeline.addLabel("colorChange", 0.7)

If the specified label doesn’t exist on the timeline, then the timeline will play from or start at the beginning of the timeline.

Timelines also support the same callback blocks as tweens, so you can use onStart(), onUpdate(), onRepeat() and onComplete() for timeline instances as well. You can also have callbacks for individual tween instances within a timeline in conjunction with callbacks on the parent timeline if you want to be notified when a particular tween has started or completed.

Refer to the example project for more detailed examples of using a Timeline.

Latest podspec

    "name": "Kinetic",
    "version": "1.1.2",
    "summary": "A super-flexible tweening library for iOS in Swift inspired by GSAP.",
    "description": "A flexible animation library written in Swift with features and usage very similar to Greensock's GSAP. Perform basic, grouped, sequential and staggered animations to achieve any type of animation, from the most basic to more complex. Supports both individual tweens and full-featured timelines to more easily create and control complex animations for multiple objects.",
    "homepage": "",
    "screenshots": [
    "license": "MIT",
    "authors": {
        "Nicholas Shipes": "[email protected]"
    "source": {
        "git": "",
        "tag": "1.1.2"
    "social_media_url": "",
    "platforms": {
        "ios": "9.0"
    "requires_arc": true,
    "source_files": "Pod/Classes/**/*",
    "frameworks": "UIKit"

Pin It on Pinterest

Share This