Curl Noise

var detail = 0.02; 

var pot_scale = 25; 

var dx = 1e-4; 

var view_scale = 5;

​

var nx = 100; 

var ny = 100; 

var vel = []; 

var particles = [];

var num_particles = 500; 

​

function setup() {

  createCanvas(nx * view_scale, ny * view_scale);

  background(0);

  loadPixels();

  // Init the velocity field

  for (var i=0; i<nx*ny; ++i) {

    vel[i] = {"x": 0, "y": 0};

  }

  // Generate the particles

  seed_particles(particles, num_particles);

}

​

function seed_particles(parts, num) {

  var center_x = nx / 2;

  var center_y = ny / 2;

  var radius = min(nx / 2, ny / 2);

  for (var p=0; p<num; ++p) {

    var rangle = random() * TWO_PI;

    var rdist = random() * radius;

    parts[p] = {"x": center_x + cos(rangle) * rdist, "y": center_y + sin(rangle) * rdist, "len": 0};

    parts[p].px = parts[p].x;

    parts[p].py = parts[p].y;

  }

}

​

function get_potential(x, y, res_x, res_y, time) {

  var distmult = pow(1 / (min(res_x, res_y)/2), 2);

  var dist_center = max(1 - (pow(x - res_x/2, 2) + pow(y - res_y/2, 2)) * distmult, 0);

  return (noise(x*detail, y*detail, time) * 2 - 1) * pot_scale * dist_center;

}

​

​

function vel_from_pot(vel_arr, res_x, res_y) {

  var time = frameCount * 0.005;

  for (var y=1; y<res_y-1; ++y) {

    for (var x=1; x<res_x-1; ++x) {

      vel_arr[IX(x,y)] = {"x": -(get_potential(x,y+dx, res_x, res_y, time) - get_potential(x,y-dx, res_x, res_y, time)) / (2*dx), 

                          "y":  (get_potential(x+dx,y, res_x, res_y, time) - get_potential(x-dx,y, res_x, res_y, time)) / (2*dx)};

    }

  }

}

​

function draw() {

  vel_from_pot(vel, nx, ny);

  fill(0, 0, 0, 10);

  noStroke();

  rect(0,0,width,height);

  for (var p=0; p<num_particles; ++p) {

    advect_particle(particles[p], vel, nx, ny);

    stroke(255 - min(int(abs(particles[p].x-particles[p].px) * 100), 255), 255 - min(int(abs(particles[p].y-particles[p].py) * 100), 255), min(int(particles[p].len * 500), 255));

    strokeWeight(particles[p].len * 3);

    line(particles[p].px * view_scale, particles[p].py * view_scale, particles[p].x * view_scale, particles[p].y * view_scale);

    particles[p].px = particles[p].x;

    particles[p].py = particles[p].y;

  }

}