// http://natureofcode.com

​

// Blob Example

// Example 5.13 adapted by Zach Lieberman

​

var physics;

​

var particles = [];

var springs = [];

var attractor;

​

function setup() {

  createCanvas(500, 500);

​

  // Initialize the physics

  physics = new VerletPhysics2D();

  physics.setDrag(0.03);

​

  for (var i = 0; i < 50; i++) {

    particles.push(new Particle(new Vec2D(random(width), random(height)), 4, 80, -1));

  }

​

  attractor = new Particle(new Vec2D(width / 2, height / 2), 100, width * 10, 0.3);

  attractor.lock();

  //attractor.set(450, 450);

​

​

  for (var i = 0; i < 50; i++) {

    var spring1 = new VerletSpring2D(particles[i], particles[(i + 1) % particles.length], 5, 0.01);

    springs.push(spring1);

    physics.addSpring(spring1);

    if (i % 5 == 0) {

      var spring2 = new VerletSpring2D(particles[i], particles[(i + 25) % particles.length], 400, 0.001);

      springs.push(spring2);

      physics.addSpring(spring2);

    }

    if ((i+5) % 10 == 0) {

      var spring2 = new VerletSpring2D(particles[i], attractor, 200, 0.001);

      springs.push(spring2);

      physics.addSpring(spring2);

    }

​

  }

​

​

}

​

function draw() {

​

  seconds = millis() / 1000;

  // Update the physics world

  physics.update();

​

  background(51);

​

  //attractor.display();

  stroke(255);

  fill(255, 20);

  beginShape();

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

    //particles[i].display();

    vertex(particles[i].x, particles[i].y);

​

    // this doesn't work the way I expect !!  I'd like to be able to change the repulsion radius over time....

    particles[i].behavior.radius = 130 + 80 * sin(seconds + i / 30.0);

    particles[i].behavior.radiusSquared = particles[i].behavior.radius * particles[i].behavior.radius;

  }

  endShape(CLOSE);

​

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

    stroke(0, 50);

    line(springs[i].a.x, springs[i].a.y, springs[i].b.x, springs[i].b.y);

  }

​

​

​

}