State Machine


It's definitely possible to use a single scene for the entire application, but for my game, I wanted to separate the states into individual scenes. So, I created a state machine to handle rendering the different scenes of the entire game.

App.ts

Recall from the Create a Scene section of the getting set up tutorial that we made an app.ts file. This is going to be our main file that handles our scene creations and rendering. Starting with the constructor, we're going to break up our scene creation and rendering loop call into separate functions.

States

How I went about this was by outlining all of the different scenes I would need for the game:

  • START
  • CUTSCENE
  • GAME
  • LOSE

The reason why there's no win and pause state is because those are actually still using the game scene and so it still needs to be able to render the game scene. I've made those two "states" as GUI overlays. Now that we know what states we want we can go ahead and create an enum for them. All the enum does is assign names to the states and encodes them as numbers. We also want to create a class variable _state to store the current state that we're in. Now, our app.ts should look something like this:

//...imports here

//enum for states
enum State { START = 0, GAME = 1, LOSE = 2, CUTSCENE = 3 }

class App {
    // General Entire Application
    private _scene: Scene;
    private _canvas: HTMLCanvasElement;
    private _engine: Engine;

    //Scene - related
    private _state: number = 0;

    constructor() {
        this._canvas = this._createCanvas();

        // initialize babylon scene and engine
        this._engine = new Engine(this._canvas, true);
        this._scene = new Scene(this._engine);

        var camera: ArcRotateCamera = new ArcRotateCamera("Camera", Math.PI / 2, Math.PI / 2, 2, Vector3.Zero(), this._scene);
        camera.attachControl(this._canvas, true);
        var light1: HemisphericLight = new HemisphericLight("light1", new Vector3(1, 1, 0), this._scene);
        var sphere: Mesh = MeshBuilder.CreateSphere("sphere", { diameter: 1 }, this._scene);

        // hide/show the Inspector
        window.addEventListener("keydown", (ev) => {
            // Shift+Ctrl+Alt+I
            if (ev.shiftKey && ev.ctrlKey && ev.altKey && ev.keyCode === 73) {
                if (this._scene.debugLayer.isVisible()) {
                    this._scene.debugLayer.hide();
                } else {
                    this._scene.debugLayer.show();
                }
            }
        });

        // run the main render loop
        this._engine.runRenderLoop(() => {
            this._scene.render();
        });
    }
}
new App();

I've also gone ahead and created a separate function for creating our canvas called _createCanvas. Additionally, here is where we'll be starting to include the use of class variables (denoted by the this keyword).

GoTo Functions

Scene Setup

The goTo functions will be in charge of setting up the scene and consist of things that happen only once.

Let's start with _goToStart for a simple example of how to set up a scene.

this._engine.displayLoadingUI();

Have the loading UI show while our start scene is loading.

this._scene.detachControl();
let scene = new Scene(this._engine);
scene.clearColor = new Color4(0,0,0,1);
let camera = new FreeCamera("camera1", new Vector3(0, 0, 0), scene);
camera.setTarget(Vector3.Zero());

Create the scene and camera. Any camera should be fine since it'll be fixed at the center of the scene, so I just went with the FreeCamera.

//...do gui related stuff

//--SCENE FINISHED LOADING--
await scene.whenReadyAsync();
this._engine.hideLoadingUI();
//lastly set the current state to the start state and set the scene to the start scene
this._scene.dispose();
this._scene = scene;
this._state = State.START;

When the scene is ready, we hide the loading UI, dispose of the current stored scene and then switch scenes and change the state to render the new scene.

VSCode users: At any point if you see an error for babylon specific components (like Color4 and FreeCamera...) hover over it and you should see a Quick Fix option, this will add it to your imports for you. If you don't see this, you can just manually add it to your imports at the top of the file

GUI setup

For now, we'll make a simple fullscreenUI with a button to transition between scenes. GUI elements will need to be imported from "@babylonjs/gui".

//... scene setup

//create a fullscreen ui for all of our GUI elements
const guiMenu = AdvancedDynamicTexture.CreateFullscreenUI("UI");
guiMenu.idealHeight = 720; //fit our fullscreen ui to this height

//create a simple button
const startBtn = Button.CreateSimpleButton("start", "PLAY");
startBtn.width = 0.2
startBtn.height = "40px";
startBtn.color = "white";
startBtn.top = "-14px";
startBtn.thickness = 0;
startBtn.verticalAlignment = Control.VERTICAL_ALIGNMENT_BOTTOM;
guiMenu.addControl(startBtn);

//this handles interactions with the start button attached to the scene
startBtn.onPointerDownObservable.add(() => {
    this._goToCutScene();
    scene.detachControl(); //observables disabled
});

Here what we're doing is creating an AdvancedDynamicTexture fullscreenUI. This is what's going to hold all of our gui elements. We then create a simple button and add an observable to detect when we click on it. This will trigger our scene to call goToCutScene. We want to make sure that we detach the controls since it's possible that as we hold down the mouse, goToCutScene gets called multiple times.

Other States

The lose state will follow a similar format, but for organizational and performance purposes, the cutscene and game states have slightly different structures.

goToLose

private async _goToLose(): Promise<void> {
    this._engine.displayLoadingUI();

    //--SCENE SETUP--
    this._scene.detachControl();
    let scene = new Scene(this._engine);
    scene.clearColor = new Color4(0, 0, 0, 1);
    let camera = new FreeCamera("camera1", new Vector3(0, 0, 0), scene);
    camera.setTarget(Vector3.Zero());

    //--GUI--
    const guiMenu = AdvancedDynamicTexture.CreateFullscreenUI("UI");
    const mainBtn = Button.CreateSimpleButton("mainmenu", "MAIN MENU");
    mainBtn.width = 0.2;
    mainBtn.height = "40px";
    mainBtn.color = "white";
    guiMenu.addControl(mainBtn);
    //this handles interactions with the start button attached to the scene
    mainBtn.onPointerUpObservable.add(() => {
        this._goToStart();
    });

    //--SCENE FINISHED LOADING--
    await scene.whenReadyAsync();
    this._engine.hideLoadingUI(); //when the scene is ready, hide loading
    //lastly set the current state to the lose state and set the scene to the lose scene
    this._scene.dispose();
    this._scene = scene;
    this._state = State.LOSE;
}

goToCutScene

The cutscene is set up normally along with the gui; however, what we do while in this state is what allows our game to be loaded properly. If you take a look at the _goToCutScene function, the scene setup is the same, but scene finished loading is slightly different. Notice how we don't have the hideLoadingUI. For now, we need to put this in, but in the final version I actually removed it since I hide it once my animations have finished loading and then trigger it to show once we've completed the dialogue, but the game is still loading.

The most important aspect is what we do after that:

var finishedLoading = false;
await this._setUpGame().then(res =>{
    finishedLoading = true;
});

Essentially what this is doing is telling the code to wait until _setUpGame has completed its tasks and then set finishedLoading to true. At this point, it may seem unnecessary to have since we haven't brought in our animation nor are we loading any heavy assets, but it's very important once we've gotten to that stage in the development process.

This was an important discovery that ultimately led me to change the structure of importing and loading assets for my game to this. If we don't wait for our assets to finish importing, what the async functions will do is tell our code to continue as we load in the background. This can ultimately break our transitions between scenes as we'd be moving on before things were fully loaded. I discovered this happening when playtesting the web-hosted version of my game:

  1. Safari had several issues relating to sounds and scene transitions
  2. Assets were taking a long time to load and thus showed undefined meshes errors

For testing purposes, we'll add in a next button that takes use straight to the game state:

//--PROGRESS DIALOGUE--
const next = Button.CreateSimpleButton("next", "NEXT");
next.color = "white";
next.thickness = 0;
next.verticalAlignment = Control.VERTICAL_ALIGNMENT_BOTTOM;
next.horizontalAlignment = Control.HORIZONTAL_ALIGNMENT_RIGHT;
next.width = "64px";
next.height = "64px";
next.top = "-3%";
next.left = "-12%";
cutScene.addControl(next);

next.onPointerUpObservable.add(() => {
    this._goToGame();
})

_setUpGame

The only thing here we need to worry about here for now is:

private async _setUpGame() {
    let scene = new Scene(this._engine);
    this._gamescene = scene;

    //...load assets
}

_setUpGame is where we are pre-creating the game scene and where we start to load all of our assets.

goToGame

If you look at the _goToGame function, we've actually encapsulated the camera setup and gui setup into their own functions. For now you can use the default UI and camera like so:

private async _goToGame(){
    //--SETUP SCENE--
    this._scene.detachControl();
    let scene = this._gamescene;
    scene.clearColor = new Color4(0.01568627450980392, 0.01568627450980392, 0.20392156862745098); // a color that fit the overall color scheme better
    let camera: ArcRotateCamera = new ArcRotateCamera("Camera", Math.PI / 2, Math.PI / 2, 2, Vector3.Zero(), scene);
    camera.setTarget(Vector3.Zero());

    //--GUI--
    const playerUI = AdvancedDynamicTexture.CreateFullscreenUI("UI");
    //dont detect any inputs from this ui while the game is loading
    scene.detachControl();

    //create a simple button
    const loseBtn = Button.CreateSimpleButton("lose", "LOSE");
    loseBtn.width = 0.2
    loseBtn.height = "40px";
    loseBtn.color = "white";
    loseBtn.top = "-14px";
    loseBtn.thickness = 0;
    loseBtn.verticalAlignment = Control.VERTICAL_ALIGNMENT_BOTTOM;
    playerUI.addControl(loseBtn);

    //this handles interactions with the start button attached to the scene
    loseBtn.onPointerDownObservable.add(() => {
        this._goToLose();
        scene.detachControl(); //observables disabled
    });

    //temporary scene objects
    var light1: HemisphericLight = new HemisphericLight("light1", new Vector3(1, 1, 0), scene);
    var sphere: Mesh = MeshBuilder.CreateSphere("sphere", { diameter: 1 }, scene);

    //get rid of start scene, switch to gamescene and change states
    this._scene.dispose();
    this._state = State.GAME;
    this._scene = scene;
    this._engine.hideLoadingUI();
    //the game is ready, attach control back
    this._scene.attachControl();
}

What we're doing here is setting up the scene normally and adding a simple button to test going to the lose state.

We've also moved our light and sphere objects to this function, using this specific scene.

Switching States

Now that we have our scenes set up, how do we actually render and switch between them?! Within the constructor of App.ts, we want to call main.

Main

The main function is where we'll be setting up our state machine. This will replace our current this._engine.runRenderLoop that we set up when we first created the scene

private async _main(): Promise<void> {
    await this._goToStart();

    // Register a render loop to repeatedly render the scene
    this._engine.runRenderLoop(() => {
        switch (this._state) {
            case State.START:
                this._scene.render();
                break;
            case State.CUTSCENE:
                this._scene.render();
                break;
            case State.GAME:
                this._scene.render();
                break;
            case State.LOSE:
                this._scene.render();
                break;
            default: break;
        }
    });

    //resize if the screen is resized/rotated
    window.addEventListener('resize', () => {
        this._engine.resize();
    });
}

We first call await _goToStart to ensure that our scene is ready to be rendered.

What this switch statement does is it tells our render loop to act differently based on the state that we're in. It might seem a little unnecessary to always be calling this._scene in each state, but this actually holds reference to our current scene. Recall that we dispose of what this._scene was, do other detachments to that scene, create a new scene, and then re-assign this._scene to the new scene. You could definitely use variables that reference your different scenes, but I thought this would be better since we're disposing of the scenes when not in use, and this ensures that we're rendering the right scene in the right state.

Now, when we run our game and progress through the states, we should see our sphere! The app.ts file should look something like this now. This is a simple, working state machine! You can modify it for whatever states you'll need.

If you're having trouble getting through the states, open the browser's inspector to see what error is being shown in the console (you might need to comment out the styling of the canvas to be able to open the inspector).

Further Reading

Previous: Getting Set Up
Next: Simple Game State

Resources

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