Contents

LottieAnimation QML Type

A Lottie player for Qt.

Import Statement: import Qt.labs.lottieqt 1.0
Inherits: Item

Properties

Signals

Methods

Detailed Description

The LottieAnimation type shows Lottie format files.

LottieAnimation is used to load and render Lottie files exported from Adobe After Effects. Currently, only subset of the full Lottie specification is supported. Most notable deviations are:

For the full list of devations, please see see the Limitations section.

Example Usage

The following example shows a simple usage of the LottieAnimation type

LottieAnimation {
    loops: 2
    quality: LottieAnimation.MediumQuality
    source: "animation.json"
    autoPlay: false
    onStatusChanged: {
        if (status === LottieAnimation.Ready) {
            // any acvities needed before
            // playing starts go here
            gotoAndPlay(startFrame);
        }
    }
    onFinished: {
        console.log("Finished playing")
    }
}

Rendering Performance

Internally, the rendered frame data is cached to improve performance. You can control the memory usage by setting the QLOTTIE_RENDER_CACHE_SIZE environment variable (default value is 2).

You can monitor the rendering performance by turning on two logging categories:

  • qt.lottieqt.lottie.render - Provides information how the animation is rendered
  • qt.lottieqt.lottie.render.thread - Provides information how the rendering process proceeds.

Specifically, you can monitor does the frame cache gets constantly full, or does the rendering process have to wait for frames to become ready. The first case implies that the animation is too complex, and the rendering cannot keep up the pace. Try making the animation simpler, or optimize the QML scene.

Property Documentation

autoPlay : bool

Defines whether the player will start playing animation automatically after the animation file has been loaded.

The default value is true.

direction : enumeration

This property holds the direction of rendering.

ConstantDescription
LottieAnimation.ForwardForward direction (Default)
LottieAnimation.ReverseReverse direction

endFrame : int

Frame number of the end of the animation. The value is available after the animation has been loaded and ready to play.

frameRate : int

This property holds the frame rate value of the Lottie animation.

frameRate changes after the asset has been loaded. Changing the frame rate does not have effect before that, as the value defined in the asset overrides the value. To change the frame rate, you can write:

LottieAnimation {
    source: "animation.json"
    onStatusChanged: {
        if (status === LottieAnimation.Ready)
            frameRate = 60;
    }
}

loops : int

This property holds the number of loops the player will repeat. The value LottieAnimation.Infinite means that the the player repeats the animation continuously.

The default value is 1.

quality : enumeration

Speficies the rendering quality of the lottie player. If LowQuality is selected the rendering will happen into a frame buffer object, whereas with other options, the rendering will be done onto QImage (which in turn will be rendered on the screen).

ConstantDescription
LottieAnimation.LowQualityAntialiasing or a smooth pixmap transformation algorithm are not used
LottieAnimation.MediumQualitySmooth pixmap transformation algorithm is used but no antialiasing (Default)
LottieAnimation.HighQualityAntialiasing and a smooth pixmap tranformation algorithm are both used

source : url

The source of the Lottie asset that LottieAnimation plays.

LottieAnimation can handle any URL scheme supported by Qt. The URL may be absolute, or relative to the URL of the component.

Setting the source property starts loading the animation asynchronously. To monitor progress of loading, connect to the status change signal.

startFrame : int

Frame number of the start of the animation. The value is available after the animation has been loaded and ready to play.

status : enumeration

This property holds the current status of the LottieAnimation element.

ConstantDescription
LottieAnimation.NullAn initial value that is used when the source is not defined (Default)
LottieAnimation.LoadingThe player is loading a Lottie file
LottieAnimation.ReadyLoading has finished successfully and the player is ready to play the animation
LottieAnimation.ErrorAn error occurred while loading the animation

For example, you could implement onStatusChanged signal handler to monitor progress of loading an animation as follows:

LottieAnimation {
    source: "animation.json"
    autoPlay: false
    onStatusChanged: {
        if (status === LottieAnimation.Ready)
            start();
    }
}

Signal Documentation

finished()

This signal is emitted when the player has finished playing. In case of looping, the signal is emitted when the last loop has been finished.

Method Documentation

double getDuration(bool inFrames)

Returns the duration of the currently playing asset.

If a given inFrames is true, the return value is the duration in number of frames. Otherwise, returns the duration in seconds.

void gotoAndPlay(int frame)

Plays the asset from the given frame.

bool gotoAndPlay(string frameMarker)

Plays the asset from the frame that has a marker with the given frameMarker. Returns true if the frameMarker was found, false otherwise.

void gotoAndStop(int frame)

Moves the playhead to the given frame and stops.

bool gotoAndStop(string frameMarker)

Moves the playhead to the given marker and stops. Returns true if frameMarker was found, false otherwise.

void pause()

Pauses the playback.

void play()

Starts or continues playing from the current position.

void start()

Starts playing the animation from the beginning.

void stop()

Stops the playback and returns to startFrame.

void togglePause()

Toggles the status of player between playing and paused states.