// Daniel Shiffman

// http://natureofcode.com

​

​

// A reference to our box2d world

let world;

​

// A list we'll use to track fixed objects

let boundaries = [];

​

// Just a single box this time

let box;

​

// The Spring that will attach to the box from the mouse

let spring;

​

​

function setup() {

  createCanvas(640, 360);

​

  // Initialize box2d physics and create the world

  world = createWorld();

​

  // Make the box

  box = new Box(width / 2, height / 2);

​

  // Make the spring (it doesn't really get initialized until the mouse is clicked)

  spring = new Spring();

​

  // Add a bunch of fixed boundaries

  boundaries.push(new Boundary(width / 2, height - 5, width, 10, 0));

  boundaries.push(new Boundary(width / 2, 5, width, 10, 0));

  boundaries.push(new Boundary(width - 5, height / 2, 10, height, 0));

  boundaries.push(new Boundary(5, height / 2, 10, height, 0));

​

}

​

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);

​

  // Always alert the spring to the new mouse position

  spring.update(mouseX, mouseY);

​

  // Draw the boundaries

  for (let i = 0; i < boundaries.length; i++) {

    boundaries[i].display();

  }

​

  // Draw the box

  box.display();

  // Draw the spring (it only appears when active)

  spring.display();

}

​

// When the mouse is released we're done with the spring

function mouseReleased() {

  spring.destroy();

}

​

// When the mouse is pressed we. . .

function mousePressed() {

  // Check to see if the mouse was clicked on the box

  if (box.contains(mouseX, mouseY)) {

    // And if so, bind the mouse position to the box with a spring

    spring.bind(mouseX, mouseY, box);

  }

}