State Machines

Playing and changing inputs in state machines

This article is out of date! Find the new version here.

For more information on designing and building state machines in Rive, please refer to the editor's state machine section.

Rive's state machines provide a way to combine a set of animations and manage the transition between them through a series of inputs that can be programmatically controlled. Once a state machine is instantiated and playing, transitioning states can be accomplished by changing boolean or double-value inputs, or firing trigger inputs. The effects of these will be dependent on how the state machine has been configured in the editor.

Playing state machines

State machines are instantiated in much the same manner as animations: provide the state machine name to the Rive object when instantiated. Ensure that the Rive instance is set to auto-play on initialization to allow the state machine to start immediately.

const r = new rive.Rive({
    src: 'https://cdn.rive.app/animations/vehicles.riv',
    canvas: document.getElementById('canvas'),
    autoplay: true,
    stateMachines: 'bumpy',
    fit: rive.Fit.cover,
});

// State Machine require the useRive hook.
export default function Simple() {
  const { RiveComponent } = useRive({
    src: 'https://cdn.rive.app/animations/vehicles.riv',
    stateMachines: "weather",
    autoplay: true,
  });

  return <RiveComponent />;
}

<canvas riv="vehicles" width="500" height="500" fit="cover">
  <riv-state-machine name="bumpy" play></riv-state-machine>
</canvas>

Set stateMachineName on the Rive component to play a single state machine.

  <Rive
    resourceName={'skills'}
    autoplay={true}
    stateMachineName="Designer's Test"
  />

To autoplay a state machine by default, simply set the stateMachines property at instantiation:

RiveAnimation.network(
    'https://cdn.rive.app/animations/vehicles.riv',
    fit: BoxFit.cover,
    stateMachines: ['bumpy'],
);

In the above snippet, at instantiation time, the runtime will create a StateMachineController reference implicitly and immediately play the state machine.

If you'd like further control over the state machine in cases where you may want to prevent autoplaying the state machine, you can instead pass your own reference to a StateMachineController to the RiveAnimation widget at instantiation time with the isActive property set to false. Below is an example of what this might look like:

class _ExampleState extends State<ExampleState> {
  /// Controller for playback
  late StateMachineController _controller;

  void _onInit(Artboard art) {
    var ctrl =
      StateMachineController.fromArtboard(art, 'some-state-machine') as StateMachineController;
    ctrl.isActive = false;
    art.addController(ctrl);
    setState(() {
      _controller = ctrl;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Play/Pause Example'),
      ),
      body: Center(
        child: RiveAnimation.asset('assets/example.riv', onInit: _onInit),
      ),
      floatingActionButton: FloatingActionButton(
        // Play/Pause the state machine
        onPressed: () => {
          _controller.isActive
              ? _controller.isActive = false
              : _controller.isActive = true
        },
        tooltip: 'Play/Pause',
        child: const Icon(Icons.arrow_upward),
      ),
    );
  }
}

As you change the isActive property of the StateMachineController, you'll see that the current state may pause advancing through the render loop. This is useful in cases where you may want to load in your Rive on screen, but delay playing until a loading sequence occurs, or some data comes back for your application.

Specify a starting state machine by setting the name of the state machine via stateMachineName when instantiating the RiveViewModel.

SwiftUI

var stateChanger = RiveViewModel(
    fileName: "skills",
    stateMachineName: "Designer's Test"
)

UIKit

class StateMachineViewController: UIViewController {
    var viewModel = RiveViewModel(
        fileName: "skills",
        stateMachineName: "Designer's Test"
    )
    
    override public func loadView() {
        super.loadView()
        
        guard let stateMachineView = view as? StateMachineView else {
            fatalError("Could not find StateMachineView")
        }
        
        viewModel.setView(stateMachineView.riveView)
    }
}

Via XML

<app.rive.runtime.kotlin.RiveAnimationView
    android:id="@+id/simple_state_machine"
    android:layout_width="match_parent"
    android:layout_height="400dp"
    app:riveResource="@raw/skills"
    app:riveStateMachine="Designer's Test" />

Via Kotlin

animationView.setRiveResource(
    R.raw.simple_state_machine,
    autoplay = true,
    stateMachineName = "Designer's Test"
)

Additionally, you can use the same APIs from animation playback (i.e play, pause, and stop) to control state machine playback, as long as you set the isStateMachine attribute to true.

animationView.play(
    "Designer's Test",
    Loop.AUTO,
    Direction.AUTO,
    isStateMachine = true
)

animationView.pause(
    "Designer's Test",
    isStateMachine = true
)

animationView.stop(
    "Designer's Test",
    isStateMachine = true
)

Controlling state machine inputs

Once the Rive file is loaded and instantiated, the state machine(s) can be queried for inputs, and these input values can be set, and in the case of triggers, fired, all programmatically.

Inputs

The web runtime provides an onLoad callback that's run when the Rive file is loaded and ready for use. We use this callback to ensure that the state machine is instantiated when we query for inputs.

<div id="button">
    <canvas id="canvas" width="1000" height="500"></canvas>
</div>
<script src="https://unpkg.com/@rive-app/canvas@2.1.0"></script>
<script>
    const button = document.getElementById('button');

    const r = new rive.Rive({
        src: 'https://cdn.rive.app/animations/vehicles.riv',
        canvas: document.getElementById('canvas'),
        autoplay: true,
        stateMachines: 'bumpy',
        fit: rive.Fit.cover,
        onLoad: (_) => {
            // Get the inputs via the name of the state machine
            const inputs = r.stateMachineInputs('bumpy');
            // Find the input you want to set a value for, or trigger
            const bumpTrigger = inputs.find(i => i.name === 'bump');
            button.onclick = () => bumpTrigger.fire();
        },
    });
</script>

We use the stateMachineInputs function on the Rive object to retrieve the inputs. Each input will have a name and type. There are three types:

StateMachineInputType.Trigger which has a fire() function
StateMachineInputType.Number which has a value number property where you can get/set the value
StateMachineInputType.Boolean which has a value boolean property where you can get/set the value

const inputs = r.stateMachineInputs('bumpy');
inputs.forEach(i => {
    const inputName = i.name;
    const inputType = i.type;
    switch(inputType) {
        case rive.StateMachineInputType.Trigger:
            i.fire();
            break;
        case rive.StateMachineInputType.Number:
            i.value = 42;
            break;
        case rive.StateMachineInputType.Boolean:
            i.value = true;
            break;
    }
});

State change event callback

We can set a callback to determine when the state machine changes state. onStateChange provides an event parameter that gives us the string name(s) of the current state(s):

const r = new rive.Rive({
    src: 'https://cdn.rive.app/animations/vehicles.riv',
    canvas: document.getElementById('canvas'),
    autoplay: true,
    stateMachines: 'bumpy',
    onStateChange: (event) => {
        stateName.innerHTML = event.data[0];
    },
});

Inputs

The react runtime provides a useStateMachineInput hook to make the process of retrieving a state machine input much simpler than that of the basic web runtime.

import { useRive, useStateMachineInput } from "@rive-app/react-canvas";

export default function Simple() {
  const { rive, RiveComponent } = useRive({
    src: "https://cdn.rive.app/animations/vehicles.riv",
    stateMachines: "bumpy",
    autoplay: true,
  });

  const bumpInput = useStateMachineInput(rive, "bumpy", "bump");

  return (
    <RiveComponent
      style={{ height: "1000px" }}
      onClick={() => bumpInput && bumpInput.fire()}
    />
  );
}

The above example shows the retrieval of a Trigger input from a named state machine. The three types of inputs are:

StateMachineInputType.Trigger which has a fire() function
StateMachineInputType.Number which has a value number property
StateMachineInputType.Boolean which has a value boolean property

State change event callback

We can set a callback to determine when the state machine changes, just like in the web runtime.

import { useEffect } from 'react';
import { useRive, useStateMachineInput } from "@rive-app/react-canvas";

export default function Simple() {
  const { rive, RiveComponent } = useRive({
    src: "https://cdn.rive.app/animations/vehicles.riv",
    stateMachines: "bumpy",
    autoplay: true,
    // We can pass the call back to the `useRive` hook
    onStateChange: (event) => {
      console.log(event.data[0]);
    }
  });

  const bumpInput = useStateMachineInput(rive, "bumpy", "bump");

  // We can also pass the callback to the rive object once it has loaded.
  // NOTE: If you pass the callback to the rive object, you do not need to
  // pass it to the useRive hook as well, and vice versa.
  useEffect(() => {
    if (rive) {
      rive.on('statechange', (event) => {
        console.log(event.data[0]);
      });
    }
  }, [rive]);

  return (
    <RiveComponent
      style={{ height: "1000px" }}
      onClick={() => bumpInput && bumpInput.fire()}
    />
  );
}

State Machine

You can listen on event & manipulate the state machine animation as any other animation:

<canvas riv="vehicles" width="500" height="500" fit="cover">
  <riv-state-machine name="bumpy" play speed="2" (load)="onload($event)"></riv-state-machine>
</canvas>

Number & Boolean Input

If the input is a number or a boolean you can use the value

<canvas riv="vehicles" width="500" height="500" fit="cover">
  <riv-state-machine name="bumpy" play (stateChange)="showStates($event)">
    <riv-input name="level" [value]="value"><riv-input>
  </riv-state-machine>
</canvas>

<input type="radio" formControl="level" value="0"> Car
<input type="radio" formControl="level" value="1"> Train
<input type="radio" formControl="level" value="2"> Airplane

The stateChange output will display the list of state changed during the same frame.

Trigger Input

If the input is a trigger you can access it with the export as rivInput:

<canvas riv="vehicles">
  <riv-state-machine name="bumpy" play>
    <riv-input #trigger="rivInput" name="bump" (change)="showInput($event)"><riv-input>
  </riv-state-machine>
</canvas>

<button (click)="trigger.fire()">Bump</button>

You can listen to the change in the input with the change Ouput.

Inputs

With the React Native runtime, most methods/triggers are available on the ref of the Rive component, including setting input values/triggering for state machines. In this case, there is no need to acquire an instance of an input. Simply set the input state from the Rive ref or fire an input state.

export default function StateMachine() {
  const riveRef = React.useRef<RiveRef>(null);
  // Maintain the values of your state machine in React state
  const [selectedLevel, setSelectedLevel] = useState('2');

  const setLevel = (n: number) => {
    setSelectedLevel(n.toString());
    // No need to acquire an instance of a state machine input, just set the
    // input state on the `riveRef` itself
    riveRef.current?.setInputState("Designer's Test", 'Level', n);
  };

  return (
    <SafeAreaView style={styles.safeAreaViewContainer}>
      <ScrollView contentContainerStyle={styles.container}>
        <Rive
          resourceName={'skills'}
          ref={riveRef}
          autoplay={true}
          stateMachineName="Designer's Test"
        />
        <RadioButton.Group
          onValueChange={(newValue) => setLevel(parseInt(newValue, 10))}
          value={selectedLevel}
        >
          <View style={styles.radioButtonsWrapper}>
            <View style={styles.radioButtonWrapper}>
              <Text>{'Beginner'}</Text>
              <RadioButton value={'0'} />
            </View>
            <View style={styles.radioButtonWrapper}>
              <Text>{'Intermediate'}</Text>
              <RadioButton value={'1'} />
            </View>
            <View style={styles.radioButtonWrapper}>
              <Text>{'Expert'}</Text>
              <RadioButton value={'2'} />
            </View>
          </View>
        </RadioButton.Group>
      </ScrollView>
    </SafeAreaView>
  );
}

See the React Native API's to learn more about the parameters for .setInputState() and .fireState()

State change event callback

We can set a callback to determine when the state machine changes.

<Rive
  resourceName={'skills'}
  autoplay={true}
  stateMachineName="Designer's Test"
  onStateChanged={(stateMachineName, stateName) => {
    console.log(
      'onStateChanged: ',
      'stateMachineName: ',
      stateMachineName,
      'stateName: ',
      stateName
    );
  }}
/>

Inputs

State machine controllers are used to retrieve a state machine's inputs which can then be used to interact with, and drive the state of a state machine.

State machine controllers require a reference to an artboard when being instantiated. The RiveAnimation widget provides a callback onInit(Artboard artboard) that is called when the Rive file has loaded and is initialized for playback:

void _onRiveInit(Artboard artboard) {}

RiveAnimation.network(
    'https://cdn.rive.app/animations/vehicles.riv',
    fit: BoxFit.cover,
    onInit: _onRiveInit,
);

In the onInit callback, you can create an instance of a StateMachineController and then retrieve the inputs you're interested in by their name. Specific inputs can be retrieved using findInput() or all inputs with the inputs property.

SMITrigger? _bump;

void _onRiveInit(Artboard artboard) {
    // Get State Machine Controller for the state machine called "bumpy"
    final controller = StateMachineController.fromArtboard(artboard, 'bumpy');
    artboard.addController(controller!);
    // Get a reference to the "bump" state machine input
    _bump = controller.findInput<bool>('bump') as SMITrigger;
}

In the above snippet, the bump input is retrieved, which is an SMITrigger. This type of input has a fire() method to activate the trigger.

class SimpleStateMachine extends StatefulWidget {
  const SimpleStateMachine({Key? key}) : super(key: key);

  @override
  _SimpleStateMachineState createState() => _SimpleStateMachineState();
}

class _SimpleStateMachineState extends State<SimpleStateMachine> {
  SMITrigger? _bump;

  void _onRiveInit(Artboard artboard) {
    final controller = StateMachineController.fromArtboard(artboard, 'bumpy');
    artboard.addController(controller!);
    _bump = controller.findInput<bool>('bump') as SMITrigger;
  }

  void _hitBump() => _bump?.fire();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Simple Animation'),
      ),
      body: Center(
        child: GestureDetector(
          child: RiveAnimation.network(
            'https://cdn.rive.app/animations/vehicles.riv',
            fit: BoxFit.cover,
            onInit: _onRiveInit,
          ),
          onTap: _hitBump,
        ),
      ),
    );
  }
}

In the complete example above, every time the RiveAnimation is tapped, it fires the bump input trigger and the state machine reacts appropriately.

Note: There are two other state machine input types to be aware of as well: SMIBool and SMINumber. These both have a value property that can get and set the value.

// Example state machine input declarations
SMIInput<bool>? _boolExampleInput;
SMIInput<double>? _numberExampleInput;

...

// Extracting inputs from the StateMachineController
void _onRiveInit(Artboard artboard) {
  final controller = StateMachineController.fromArtboard(artboard, 'example');
  artboard.addController(controller!);
  _boolExampleInput = controller.findInput<bool>('exampleBool') as SMIBool;
  _numberExampleInput = controller.findInput<double>('exampleNum') as SMINumber;
}

...

// Getting/setting state machine input values
if (_boolExampleInput.value == false) {
  _boolExampleInput.value = true;
}
if (_numberExampleInput.value >= 100) {
  _numberExampleInput.value = 0;
}

State change event callback

If you'd like to know which state a state machine is in, or when a state machine transitions to another state, you can provide a callback to StateMachineController. The callback has the name of the state machine and the name of the animation associated with the state transitioned to:

 void _onRiveInit(Artboard artboard) {
  final controller = StateMachineController.fromArtboard(
    artboard,
    'bumpy',
    onStateChange: _onStateChange,
  );
  artboard.addController(controller!);
  _bump = controller.findInput<bool>('bump') as SMITrigger;
}

void _onStateChange(
  String stateMachineName,
  String stateName,
) =>
    setState(
      () => message = 'State Changed in $stateMachineName to $stateName',
    );

Inputs

Just like with animation playback controls, setting input values for state machines goes through the RiveViewModel instantiated in the View class.

.setInput()

inputName (String) - Name of the input on a state machine to set a value for
value (Bool, Float, or Double) - value to set for the associated inputName

triggerInput()

inputName (String) - Name of the input on a state machine to trigger

// Example of a number input
starsVM.setInput("Rating Changed", value: 5)

// Example of a boolean input
toggleVM.setInput("Switch Flipped", value: true)

// Example of a trigger input
confettiVM.triggerInput("Celebrate")

State change event callbacks

This runtime allows for delegates that can be set on the RiveViewModel. If provided, these delegate functions will be fired whenever a matching event is triggered to be able to hook into and listen for certain events in the Rive animation cycle.

Currently, there exist the following delegates:

RivePlayerDelegate - Hook into animation and state machine lifecycle events
- player: (loopedWithModel riveModel: RiveModel?, type: Int) {}
- player: (playedWithModel riveModel: RiveModel?) {}
- player: (pausedWithModel riveModel: RiveModel?) {}
- player: (stoppedWithModel riveModel: RiveModel?) {}
RiveStateMachineDelegate - Hook into state changes on a state machine lifecycle
- stateMachine: (_ stateMachine: RiveStateMachineInstance, didStateChange stateName: String) {}

You can create your own delegate or mix in with the RiveViewModel, implementing as many protocols as are needed. Below is an example of how to customize a RiveViewModel's implementation of the RivePlayerDelegate:

class SimpleAnimation: RiveViewModel {
    init() {
        let model = RiveModel(fileName: "truck_v7", stateMachineName: "Drive")
        super.init(model)
    }
    
    override func setView(rview view: RiveView) {
        super.setView(view)
        rview?.playerDelegate = self
        rview?.stateMachineDelegate = self
    }

    override func player(playedWithModel riveModel: RiveModel?) {
        if let stateMachineName = riveModel?.stateMachine?.name() {...}
    }
    
    override func player(pausedWithModel riveModel: RiveModel?) {
        if let stateMachineName = riveModel?.stateMachine?.name() {...}
    }
    
    override func player(stoppedWithModel riveModel: RiveModel?) {
        if let stateMachineName = riveModel?.stateMachine?.name() {...}
    }
    
    @objc func stateMachine(_ stateMachine: RiveStateMachineInstance, didChangeState stateName: String) {
        var stateMachineNames: [String] = []
        var stateMachineStates: [String] = []
        stateMachineNames.append(stateMachine.name())
        stateMachineStates.append(stateName)
        ...
    }
}

Inputs

Just like other methods within the rive-android runtime, use the view to set values on a state machine input. In this case, there is no need to grab references to state machine input instances to set values.

There are 3 different methods to set input values or trigger inputs for number, boolean, and trigger inputs respectively:

.setNumberState(stateMachineName: String, inputName: String, value: Float)
.setBooleanState(stateMachineName: String, inputName: String, value: Boolean)
.fireState(stateMachineName: String, inputName: String)

// i.e Set input state on a number input
animationView.setNumberState("Designer's Test", "Level", 0f)

// i.e Set boolean state on a boolean input
animationView.setBooleanState("Boolean test", "foo", true)

// i.e Fire a trigger input
animationView.fireState("Trigger test", "fireInput");

State change event callback

To listen for state changes, when creating a Listener to register on your animation view, you can add the following callback, where you'll receive the name of the state machine, and the state it transitions to:

val listener = object : Listener {
    override fun notifyStateChanged(stateMachineName: String, stateName: String) {
        // Do something
    }
}
animationView.registerListener(listener)

Rive Listeners

If your Rive file has Rive Listeners and you've configured your Rive instance with a state machine according to the steps outlined per runtime above, there is no additional configuration or options needed to enable the pointer events to be captured on the Rive instance. The event capturing is handled internally by the Rive widget/component.

However, if you are going about constructing your own render loop and using low-level APIs to drive Rive content, (i.e., low-level WASM), you may need to set up event listeners manually to capture user interaction and pass feedback down to the state machine (i.e. see setup in JS).

Last updated 7 months ago