Lottie QtQuick

This is Lottie for Qt. It was not invented by us and most of the code was directly ported from the iOS Objective-C code.

Introduction
Installing Lottie
Sample App
Code Examples
Debugging Lottie
Changing Animations At Runtime
Animated Controls and Switches
Adding Subviews to Animation
Supported After Effects Features
Currently Unsupported After Effects Features
Community Contributions
Alternatives
Why is it called Lottie?
Contributing
Issues or feature requests?

Introduction

Lottie is a mobile library for Android and iOS that parses Adobe After Effects animations exported as json with bodymovin and renders the vector animations natively all platforms using the QtQuick scene graph!

For the first time, designers can create and ship beautiful animations without an engineer painstakingly recreating it by hand. Since the animation is backed by JSON they are extremely small in size but can be large in complexity! Animations can be played, resized, looped, sped up, slowed down, reversed, and even interactively scrubbed. Lottie can play or loop just a portion of the animation as well, the possibilities are endless! Animations can even be changed at runtime in various ways! Change the color, position or any keyframable value! Lottie also supports native UIViewController Transitions out of the box!

Here is just a small sampling of the power of Lottie

Installing Lottie

Github Repo

You can pull the Lottie Github Repo and include the Lottie.xcodeproj to build a dynamic or static library.

qpm

TBD

Sample App

Clone this repo and try out the Sample App The repo can build a macOS Example and an iOS Example

The iOS Example App demos several of the features of Lottie

The animation Explorer allows you to scrub, play, loop, and resize animations. Animations can be loaded from the app bundle or from Lottie Files using the built in QR Code reader.

Code Examples

Lottie animations can be loaded from bundled JSON or from a URL To bundle JSON just add it and any images that the animation requires to your target in xcode.

LOTAnimationView *animation = [LOTAnimationView animationNamed:@"Lottie"];
[self.view addSubview:animation];
[animation playWithCompletion:^(BOOL animationFinished) {
  // Do Something
}];

If you are working with multiple bundles you can use.

LOTAnimationView *animation = [LOTAnimationView animationNamed:@"Lottie" inBundle:[NSBundle YOUR_BUNDLE]];
[self.view addSubview:animation];
[animation playWithCompletion:^(BOOL animationFinished) {
  // Do Something
}];

Or you can load it programmatically from a NSURL

LOTAnimationView *animation = [[LOTAnimationView alloc] initWithContentsOfURL:[NSURL URLWithString:URL]];
[self.view addSubview:animation];

Lottie supports the iOS UIViewContentModes aspectFit, aspectFill and scaleFill

You can also set the animation progress interactively.

CGPoint translation = [gesture getTranslationInView:self.view];
CGFloat progress = translation.y / self.view.bounds.size.height;
animationView.animationProgress = progress;

Or you can play just a portion of the animation:

[lottieAnimation playFromProgress:0.25 toProgress:0.5 withCompletion:^(BOOL animationFinished) {
  // Do Something
}];

Debugging

Lottie has a couple of debugging features to know about. When an animation is loaded unsupported features are logged out in the console with their function names.

If you checkout LOTHelpers.h you will see two debug flags. ENABLE_DEBUG_LOGGING and ENABLE_DEBUG_SHAPES. ENABLE_DEBUG_LOGGING increases the verbosity of Lottie Logging. It logs anytime an animation node is set during animation. If your animation if not working, turn this on and play your animation. The console log might give you some clues as to whats going on.

ENABLE_DEBUG_SHAPES Draws a colored square for the anchor-point of every layer and shape. This is helpful to see if anything is on screen.

Keypaths

LOTAnimationView provides - (void)logHierarchyKeypaths which will recursively log all settable keypaths for the animation. This is helpful for changing animationations at runtime.

Adding Views to an Animation at Runtime

Not only can you change animations at runtime with Lottie, you can also add custom UI to a LOTAnimation at runtime. The example below shows some advance uses of this to create a dynamic image loader.

A Dynamic Image Loading Spinner

The example above shows a single LOTAnimationView that is set with a loading spinner animation. The loading spinner loops a portion of its animation while an image is downloaded asynchronously. When the download is complete, the image is added to the animation and the rest of the animation is played seamlessly. The image is cleanly animated in and a completion block is called.

Now, the animation has been changed by a designer and needs to be updated. All that is required is updating the JSON file in the bundle. No code change needed!

Here, the design has decided to add a 'Dark Mode' to the app. Just a few lines of code change the color of the animation at runtime.

Pretty powerful eh?

Check out the code below for an example!

import UIKit
import Lottie

class ViewController: UIViewController {
  
  var animationView: LOTAnimationView = LOTAnimationView(name: "SpinnerSpin");
  
  override func viewDidLoad() {
    super.viewDidLoad()
    
    // Setup our animaiton view
    animationView.contentMode = .scaleAspectFill
    animationView.frame = CGRect(x: 20, y: 20, width: 200, height: 200)

    self.view.addSubview(animationView)
    // Lets change some of the properties of the animation
    // We arent going to use the MaskLayer, so lets just hide it
    animationView.setValue(0, forKeypath: "MaskLayer.Ellipse 1.Transform.Opacity", atFrame: 0)
    // All of the strokes and fills are white, lets make them DarkGrey
    animationView.setValue(UIColor.darkGray, forKeypath: "OuterRing.Stroke.Color", atFrame: 0)
    animationView.setValue(UIColor.darkGray, forKeypath: "InnerRing.Stroke.Color", atFrame: 0)
    animationView.setValue(UIColor.darkGray, forKeypath: "InnerRing.Fill.Color", atFrame: 0)
    
    // Lets turn looping on, since we want it to repeat while the image is 'Downloading'
    animationView.loopAnimation = true
    // Now play from 0 to 0.5 progress and loop indefinitely.
    animationView.play(fromProgress: 0, toProgress: 0.5, withCompletion: nil)
    
    // Lets simulate a download that finishes in 4 seconds.
    let dispatchTime = DispatchTime.now() + 4.0
    DispatchQueue.main.asyncAfter(deadline: dispatchTime) {
      self.simulateImageDownloaded()
    }
  }
  
  func simulateImageDownloaded() {
    // Our downloaded image
    let image = UIImage(named: "avatar.jpg")
    let imageView = UIImageView(image: image)

    // We want the image to show up centered in the animation view at 150Px150P
    // Convert that rect to the animations coordinate space
    // The origin is set to -75, -75 because the origin is centered in the animation view
    let imageRect = animationView.convert(CGRect(x: -75, y: -75, width: 150, height: 150), toLayerNamed: nil)
    
    // Setup our image view with the rect and add rounded corners
    imageView.frame = imageRect
    imageView.layer.masksToBounds = true
    imageView.layer.cornerRadius = imageRect.width / 2;
    
    // Now we set the completion block on the currently running animation
    animationView.completionBlock = { (result: Bool) in ()
      // Add the image view to the layer named "TransformLayer"
      self.animationView.addSubview(imageView, toLayerNamed: "TransformLayer", applyTransform: true)
      // Now play the last half of the animation
      self.animationView.play(fromProgress: 0.5, toProgress: 1, withCompletion: { (complete: Bool) in
        // Now the animation has finished and our image is displayed on screen
        print("Image Downloaded and Displayed")
      })
    }
    
    // Turn looping off. Once the current loop finishes the animation will stop 
    // and the completion block will be called.
    animationView.loopAnimation = false
  }
  
}

Changing Animations At Runtime

Lottie can do more than just play beautiful animations. Lottie allows you to change animations at runtime.

Say we want to create 4 toggle switches.

Its easy to create the four switches and play them:

let animationView = LOTAnimationView(name: "toggle");
self.view.addSubview(animationView)
animationView.frame.origin.x = 40
animationView.frame.origin.y = 20
animationView.autoReverseAnimation = true
animationView.loopAnimation = true
animationView.play()

let animationView2 = LOTAnimationView(name: "toggle");
self.view.addSubview(animationView2)
animationView2.frame.origin.x = 40
animationView2.frame.origin.y = animationView.frame.maxY + 4
animationView2.autoReverseAnimation = true
animationView2.loopAnimation = true
animationView2.play()

let animationView3 = LOTAnimationView(name: "toggle");
self.view.addSubview(animationView3)
animationView3.frame.origin.x = 40
animationView3.frame.origin.y = animationView2.frame.maxY + 4
animationView3.autoReverseAnimation = true
animationView3.loopAnimation = true
animationView3.play()

let animationView4 = LOTAnimationView(name: "toggle");
self.view.addSubview(animationView4)
animationView4.frame.origin.x = 40
animationView4.frame.origin.y = animationView3.frame.maxY + 4
animationView4.autoReverseAnimation = true
animationView4.loopAnimation = true
animationView4.play()

Now lets change their colors

animationView2.setValue(UIColor.green, forKeypath: "BG-On.Group 1.Fill 1.Color", atFrame: 0)
animationView3.setValue(UIColor.red, forKeypath: "BG-On.Group 1.Fill 1.Color", atFrame: 0)
animationView4.setValue(UIColor.orange, forKeypath: "BG-On.Group 1.Fill 1.Color", atFrame: 0)

[animationView2 setValue:[UIColor greenColor] forKeypath:@"BG-On.Group 1.Fill 1.Color" atFrame:@0];

The keyPath is a dot separated path of layer and property names from After Effects. LOTAnimationView provides - (void)logHierarchyKeypaths which will recursively log all settable keypaths for the animation. "BG-On.Group 1.Fill 1.Color"

Now lets change a couple of properties

animationView2.setValue(UIColor.green, forKeypath: "BG-On.Group 1.Fill 1.Color", atFrame: 0)
animationView2.setValue(UIColor.red, forKeypath: "BG-Off.Group 1.Fill 1.Color", atFrame: 0)

Lottie allows you to change any property that is animatable in After Effects. If a keyframe does not exist, a linear keyframe is created for you. If a keyframe does exist then just its data is replaced.

Animated Controls and Switches

Lottie also has a custom subclass of UIControl for creating custom animatable interactive controls. Currently Lottie has LOTAnimatedSwitch which is a toggle style switch control. Tapping on the switch plays either the On-Off or Off-On animation and sends out a UIControlStateValueChanged broadcast to all targets. It is used in the same way UISwitch is used with a few additions to setup the animation with Lottie.

You initialize the switch either using the conveneince method or by supplying the animation directly.

// Convenience
LOTAnimatedSwitch *toggle1 = [LOTAnimatedSwitch switchNamed:@"Switch"];
 
// Manually 
LOTComposition *comp = [LOTComposition animationNamed:@"Switch"];
LOTAnimatedSwitch *toggle1 = [[LOTAnimatedSwitch alloc] initWithFrame:CGRectZero];
[toggle1 setAnimationComp:comp];

You can also specify a specific portion of the animation's timeline for the On and Off animation. By default LOTAnimatedSwitch will play the animation forward for On and backwards for off.

Lets say that the supplied animation animates ON from 0.5-1 progress and OFF from 0-0.5:

/// On animation is 0.5 to 1 progress.
[toggle1 setProgressRangeForOnState:0.5 toProgress:1];

/// Off animation is 0 to 0.5 progress.
[toggle1 setProgressRangeForOffState:0 toProgress:0.5];

Also, all LOTAnimatedControls add support for changing appearance for state changes. This requires some setup in After Effects. Lottie will switch visible animated layers based on the controls state. This can be used to have Disabled, selected, or Highlighted states. These states are associated with layer names in After Effects, and are dynamically displayed as the control changes states.

Lets say we have a toggle switch with a Normal and Disabled state. In Effects we have a composition that contains Precomps of the regular "Button" and disabled "Disabled" states. They have different visual styles.

Now in code we can associate UIControlState with these layers

// Specify the layer names for different states
[statefulSwitch setLayerName:@"Button" forState:UIControlStateNormal];
[statefulSwitch setLayerName:@"Disabled" forState:UIControlStateDisabled];

// Changes visual appearance by switching animation layer to "Disabled"
statefulSwitch.enabled = NO;

// Changes visual appearance by switching animation layer to "Button"
statefulSwitch.enabled = YES;

Supported After Effects Features

Keyframe Interpolation

Linear Interpolation
Bezier Interpolation
Hold Interpolation
Rove Across Time
Spatial Bezier

Solids

Transform Anchor Point
Transform Position
Transform Scale
Transform Rotation
Transform Opacity

Masks

Path
Opacity
Multiple Masks (additive, subtractive and intersection)

Track Mattes

Alpha Matte

Parenting

Multiple Parenting
Nulls

Shape Layers

Anchor Point
Position
Scale
Rotation
Opacity
Path
Group Transforms (Anchor point, position, scale etc)
Rectangle (All properties)
Eclipse (All properties)
Multiple paths in one group
Even-Odd winding paths
Reverse Fill Rule

Stroke (shape layer)

Stroke Color
Stroke Opacity
Stroke Width
Line Cap
Dashes (Now Animated!)

Fill (shape layer)

Fill Color
Fill Opacity

Trim Paths (shape layer)

Trim Paths Start
Trim Paths End
Trim Paths Offset

Repeaters

Supports repeater transforms
Offset currently not supported.

Gradients

Support for Linear Gradients
Support for Radial Gradients

Polystar and Polygon

Supported! Theres a known bug if the roundness is greater than 100 percent.

Layer Features

Precomps
Image Layers
Shape Layers
Null Layers
Solid Layers
Parenting Layers
Alpha Matte Layers

Currently Unsupported After Effects Features

Merge Shapes
Alpha Inverted Masks
Trim Shapes Individually feature of Trim Paths
Expressions
3d Layer support
Time remapping / Layer Reverse
Layer Blend Modes
Layer Effects

Alternatives

Build animations by hand. Building animations by hand is a huge time commitment for design and engineering, even with QtQuick. It's often hard or even impossible to justify spending so much time to get an animation right.
Gifs. Gifs are more than double the size of a bodymovin JSON and are rendered at a fixed size that can't be scaled up to match large and high density screens.
Png sequences. Png sequences are even worse than gifs in that their file sizes are often 30-50x the size of the bodymovin json and also can't be scaled up.

Why is it called Lottie?

Lottie is named after a German film director and the foremost pioneer of silhouette animation. Her best known films are The Adventures of Prince Achmed (1926) – the oldest surviving feature-length animated film, preceding Walt Disney's feature-length Snow White and the Seven Dwarfs (1937) by over ten years The art of Lotte Reineger

Contributing

Contributors are more than welcome. Just upload a PR with a description of your changes.

If you would like to add more JSON files feel free to do so!

Issues or feature requests?

TBD

Known bugs of the QtQuick port

Watermelon example renders strangely
Switch example renders strangely
Dashes not tested
Masking not implemented
Gradients not implemented
Memory leaks not checked yet
Every frame recreates all scene graph nodes
Line caps are sometimes not round enough. This is caused by scaling though the scene graph. Should be changed to value delegates.
No "autoReverseAnimation" property
No LOTAnimatableSwitch implementation for now
Typewriter cursor is not blinking
playToFrame and other helpers are missing

Files

README-old.md

Latest commit

History