The basics behind “Fling” Unity game built in HTML5 with Phaser and Matter.js

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Did you play Fling?

It’s a 2D platforming game with Grappling Hook as the only way to move, similar to my Mickey Hooks prototype, but the main difference is you actually fire the hook rather than tapping on the body you want to grapple. Something very similar to the Ninja Rope used in Worms game series.

So I changed a bit the code used in Mickey Hooks, I have to say Matter.js was a bit unstable when reducing constraints so I will need to find a workaroud to make things work better, anyway this is what I have to show you at the moment:

Click the mouse to fire a hook from your hero – the small box – once the hook grapples on a box, you can start swinging. For stability reasons, grapple and constraints are destroyed once the box collides with an obstacle or when the hero gets too close to the hook.

This is the source code, completely commented but there’s still a lot to do. I want the constraint to work better, will study on it.

let game;
let gameOptions = {
    gravity: 1,             // game gravity
    terrainObjects: 20,     // amount of terrain objects
    heroSize: 20,           // hero size
    constraintSpeed: 2,     // constraint shrinkage speed
    minBoxSize: 50,         // minimum box size
    maxBoxSize: 200,        // maximum box size
    hookSpeed: 20           // speed use to fire the hook
}
const WALL = 0;
const BALL = 1;
const HOOK = 2;
window.onload = function() {

    // game configuration
    let gameConfig = {
        type: Phaser.AUTO,
        scale: {
            mode: Phaser.Scale.FIT,
            autoCenter: Phaser.Scale.CENTER_BOTH,
            parent: "thegame",
            width: 1334,
            height: 750
        },
        scene: playGame,
        physics: {
            default: "matter",
            matter: {
                gravity: {
                    y: gameOptions.gravity
                },
                debug: true
            }
        }
    }
    game = new Phaser.Game(gameConfig);
    window.focus();
}
class playGame extends Phaser.Scene{
    constructor(){
        super("PlayGame");
    }
    create(){

        // I want physics world to be updated 30 times per second
        this.matter.world.update30Hz();

        // adding world bounds. Basically four walls
        this.matter.world.setBounds(10, 10, game.config.width - 20, game.config.height - 20);

        // placing some random static boxes labeled as WALL
        for (let i = 0; i < gameOptions.terrainObjects; i++){
            let posX = Phaser.Math.Between(0, game.config.width);
            let posY = Phaser.Math.Between(0, game.config.height);
            let width = Phaser.Math.Between(gameOptions.minBoxSize, gameOptions.maxBoxSize);
            let height = Phaser.Math.Between(gameOptions.minBoxSize, gameOptions.maxBoxSize);
            let poly = this.matter.add.rectangle(posX, posY, width, height, {
                isStatic: true
            });
            poly.label = WALL;
        }

        // adding a bouncing ball labeled as BALL
        this.hero = this.matter.add.rectangle(game.config.width / 2, game.config.height / 2, gameOptions.heroSize, gameOptions.heroSize, {
            restitution: 0.5
        });
        this.hero.label = BALL;

        // the hook
        this.hook = null;

        // event listeners
        this.input.on("pointerdown", this.fireHook, this);

        // no ropes at the beginning
        this.rope = null;

        // collision listener
        this.matter.world.on("collisionstart", function(e, b1, b2){

            // when the ball collides with something, we'll remove the hook
            if(b1.label == BALL || b2.label == BALL){
                this.releaseHook();
                return;
            }

            // when the hook collides with something, let's make it static and create the joint
            if((b1.label == HOOK || b2.label == HOOK) && !this.rope){

                // make the hook static
                Phaser.Physics.Matter.Matter.Body.setStatic(this.hook, true);

                // calculate the distance between the ball and the hook
                let distance = Phaser.Math.Distance.Between(this.hero.position.x, this.hero.position.y, this.hook.position.x, this.hook.position.y);

                // is the distance fairly greater than hero size?
                if(distance > gameOptions.heroSize * 2){

                    // add the constraint
                    this.rope = this.matter.add.constraint(this.hero, this.hook, distance, 0);
                }

            }
        }, this)
    }

    // method to fire the hook
    fireHook(e){

        // destroy current constraint
        this.releaseHook();

        // calculate the angle between the pointer and the ball
        let angle = Phaser.Math.Angle.Between(this.hero.position.x, this.hero.position.y, e.position.x, e.position.y);

        this.hook = this.matter.add.rectangle(this.hero.position.x + (gameOptions.heroSize * 2) * Math.cos(angle), this.hero.position.y + (gameOptions.heroSize * 2) * Math.sin(angle), 10, 10);
        this.hook.label = HOOK;

        // give the hook the proper velocity
        Phaser.Physics.Matter.Matter.Body.setVelocity(this.hook, {
            x: gameOptions.hookSpeed * Math.cos(angle),
            y:gameOptions.hookSpeed * Math.sin(angle)
        });
    }

    // method to remove the hook
    releaseHook(){

        // is there a constraint? Remove it
        if(this.rope){
            this.matter.world.removeConstraint(this.rope);
            this.rope = null;
        }

        if(this.hook){
            this.matter.world.remove(this.hook);
        }
    }

    // method to be executed at every frame
    update(){

        // is there a constraint? Shrink it
        if(this.rope){
            this.rope.length -= gameOptions.constraintSpeed;

            // rope too short? Remove it
            if(this.rope.length <= gameOptions.heroSize * 2){
                this.releaseHook();
            }
        }
    }
};

I will also try to build it with Unity, meanwhile download the source code.

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