​

var particles = [];

var n = 500;//number of particle

var noiseScale = 100;//noise scale;

​

function setup() {

  createCanvas(500, 500);

  background(10);

  noiseDetail(1, 0);

  console.log(pixelDensity());

  //generate noise image

  genNoiseImg();

  image(noiseImg, 0, 0);

  //initialize particle

  for(var i=0; i<n; i++){

    var particle = new Object();

    particle.pos = createVector(random(width), random(height));

    particles.push(particle);//add particle to particle list

  }

}

​

​

//get gradient vector

function curl(x, y){

  var EPSILON = 0.001;//sampling interval

  //Find rate of change in X direction

  var n1 = noise(x + EPSILON, y);

  var n2 = noise(x - EPSILON, y);

  //Average to find approximate derivative

  var cx = (n1 - n2)/(2 * EPSILON);

​

  //Find rate of change in Y direction

  n1 = noise(x, y + EPSILON);

  n2 = noise(x, y - EPSILON);

​

  //Average to find approximate derivative

  var cy = (n1 - n2)/(2 * EPSILON);

  //return new createVector(cx, cy);//gradient toward higher position

  return new createVector(cy, -cx);//rotate 90deg

}

​

function draw() {

  tint(255, 3) //decides how long the tint of each particle will last

  image(noiseImg, 0, 0);//fill with transparent noise image

  //fill(0, 4);

  //rect(0, 0, width, height);

  strokeWeight(4);//particle size

  // stroke(random(255,30,60));

  stroke(random(255,500));

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

    var p = particles[i];//pick a particle

    p.pos.add(curl(p.pos.x/noiseScale, p.pos.y/noiseScale));

    point(p.pos.x, p.pos.y);

  }

}

​

function genNoiseImg(){

  noiseImg = createGraphics(width, height);

  noiseImg.loadPixels();

  var widthd = width*pixelDensity();

  var heightd = height*pixelDensity();

  for(var i=0; i<widthd; i++){

    for(var j=0; j<heightd; j++){

      var x = i/pixelDensity();

      var y = j/pixelDensity();

      var bright = pow(noise(x/noiseScale, y/noiseScale)-0.3, 1/2.0)*400;

      noiseImg.pixels[(i+j*widthd)*4] = bright;

      noiseImg.pixels[(i+j*widthd)*4+1] = bright;

      noiseImg.pixels[(i+j*widthd)*4+2] = bright;

      noiseImg.pixels[(i+j*widthd)*4+3] = 255;

    }

  }

  noiseImg.updatePixels();

}