// Daniel Shiffman

// http://natureofcode.com

​

// Reference to physics world

var physics;

​

var particles = [];

var attractor;

​

function setup() {

  createCanvas(640, 360);

​

  // Initialize the physics

  physics = new VerletPhysics2D();

  physics.setDrag(0.01);

  for (var i = 0; i < 50; i++) {

    particles.push(new Particle(new Vec2D(random(width), random(height)), 4, 16, -1));

  }

  attractor = new Particle(new Vec2D(width / 2, height / 2), 24, width, 0.1);

​

​

}

​

function draw() {

​

  // Update the physics world

  physics.update();

​

  background(0);

​

  attractor.display();

  for (var i = 0; i < particles.length; i++) {

    particles[i].display();

  }

  // Move the second one according to the mouse

  if (mouseIsPressed) {

    attractor.lock();

    attractor.set(mouseX, mouseY);

  } else {

    attractor.unlock();

  }

}