// Daniel Shiffman

// http://natureofcode.com

​

// A reference to our box2d world

let world;

​

// A list for all of our particles

let particles = [];

​

let wall;

​

function setup() {

  createCanvas(640, 360);

​

  // Initialize box2d physics and create the world

  world = createWorld();

​

  world.SetContactListener(new CustomListener());

​

  wall = new Boundary(width / 2, height - 5, width, 10);

}

​

function draw() {

  background(0);

​

  // We must always step through time!

  let timeStep = 1.0 / 30;

  // 2nd and 3rd arguments are velocity and position iterations

  world.Step(timeStep, 10, 10);

​

  if (random(1) < 0.1) {

    let sz = random(4, 8);

    particles.push(new Particle(random(width), 20, sz));

  }

​

​

  // Look at all particles

  for (let i = particles.length - 1; i >= 0; i--) {

    particles[i].display();

    // Particles that leave the screen, we delete them

    // (note they have to be deleted from both the box2d world and our list

    if (particles[i].done()) {

      particles.splice(i, 1);

    }

  }

​

  wall.display();

​

}