const Bodies = Matter.Bodies;

const World = Matter.World;

const Constraint = Matter.Constraint;

const Mouse = Matter.Mouse;

const MouseConstraint = Matter.MouseConstraint;

​

let ground;

let boxes = [];

let world;

let engine;

let rock;

let mConstraint;

let slingshot;

​

function setup() {

  let canvas = createCanvas(600, 400);

  engine = Engine.create();

  world = engine.world;

  ground = new Boundary(0, 380, width, 20);

​

  for (let i = 0; i < 3; i++) {

    box = new Box(500, 300 - i * 100, 25, 75);

    boxes.push(box);

  }

  rock = new Rock(150, 320, 10);

​

  let canvasmouse = Mouse.create(canvas.elt);

  canvasmouse.pixelRatio = pixelDensity();

  let options = {

    mouse: canvasmouse

  }

  mConstraint = MouseConstraint.create(engine, options);

  World.add(world, mConstraint);

​

  slingshot = Constraint.create({

    pointA: {

      x: 150,

      y: 300

    },

    bodyB: rock.body,

    length: 20,

    stiffness: 0.01

  });

  World.add(world, slingshot);

​

​

}

​

​

function keyPressed() {

  rock = new Rock(150, 320, 10);

 slingshot.bodyB = rock.body; 

}

​

​

function draw() {

  background(0);

  Engine.update(engine);

  ground.show();

  for (let box of boxes) {

    box.show();

  }

  rock.show();

​

  let posR = rock.body.position;

  let posS = slingshot.pointA;

  if (!mouseIsPressed) {

    let d = dist(posR.x, posR.y, posS.x, posS.y);

    if (d > 60 && posR.x > 150) {

      slingshot.bodyB = null;

    }

  }

​

​

  if (slingshot.bodyB) {

    stroke(255);

    line(slingshot.pointA.x, slingshot.pointA.y, rock.body.position.x, rock.body.position.y);

  }

}