code

var particles = [];
var bg = "#202020";;

function setup() {
  createCanvas(540, 540);
  colorMode(HSB, 360, 1, 1);
}

function draw() {
  background(bg);
  for (var i = 0; i < particles.length; i++) {
    particles[i].update();
    particles[i].paint();
  }
}

function mousePressed() {
  particles.push(new Particle(mouseX, mouseY));
}

function keyPressed() {
  saveFrames("anim/image-", "png", 5, 30);
}

function Particle(x, y) {
  this.x = x;
  this.y = y;
  this.history = [];
  this.baseCol = random(360);
  var maxParts = 25; //, n = frameCount;

  this.update = function() {
    var r = 10;
    this.x += random(-r, r);
    this.y += random(-r, r);
    /* var nx = map(noise((n+frameCount)/1),0,1,-r,r);
    var ny = map(noise((2*n+frameCount)/1),0,1,-r,r);
    this.x += nx;
    this.y += ny;
    */
    var v = createVector(this.x, this.y);
    this.history.push(v);
    if (this.history.length > maxParts) {
      this.history.splice(0, 1);
    }
  }

  this.paint = function() {
    for (var i = 0; i < this.history.length; i++) {
      var sz = map(i, 0, maxParts - 1, 0, 25);
      var pos = this.history[i];
      stroke(bg);
      fill(this.baseCol + random(-50, 50), .9, .9);
      ellipse(pos.x, pos.y, sz, sz);
    }
  }
}