let particles = [];

let particleCount = 1000;

let flowField;

let scl = 20;

let cols, rows;

​

function setup() {

  createCanvas(640, 480);

  capture = createCapture(VIDEO);

  capture.size(640, 480);

  capture.hide();

​

  cols = floor(width / scl);

  rows = floor(height / scl);

  flowField = new Array(cols * rows);

​

  for (let i = 0; i < particleCount; i++) {

    particles[i] = new Particle();

  }

​

  background(0);

}

​

function draw() {

  capture.loadPixels();

  // Calculate flow field

  let yoff = 0;

  for (let y = 0; y < rows; y++) {

    let xoff = 0;

    for (let x = 0; x < cols; x++) {

      let index = x + y * cols;

      let angle = noise(xoff, yoff, frameCount * 0.01) * TWO_PI * 4;

      let v = p5.Vector.fromAngle(angle);

      v.setMag(1);

      flowField[index] = v;

      xoff += 0.1;

    }

    yoff += 0.1;

  }

​

  for (let particle of particles) {

    particle.follow(flowField);

    particle.update();

    particle.edges();

    particle.show();

  }

}

​

class Particle {

  constructor() {

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

    this.vel = createVector(0, 0);

    this.acc = createVector(0, 0);

    this.maxSpeed = 4;

    this.prevPos = this.pos.copy();

  }

​

  update() {

    this.vel.add(this.acc);

    this.vel.limit(this.maxSpeed);

    this.pos.add(this.vel);

    this.acc.mult(0);

  }

​

  follow(vectors) {

    let x = floor(this.pos.x / scl);

    let y = floor(this.pos.y / scl);

    let index = x + y * cols;

    let force = vectors[index];

    this.applyForce(force);

  }

​

  applyForce(force) {

    this.acc.add(force);

  }

​

  show() {

    let pixelColor = capture.get(floor(this.pos.x), floor(this.pos.y));

    stroke(pixelColor[0], pixelColor[1], pixelColor[2], 50);

    strokeWeight(1);

    line(this.pos.x, this.pos.y, this.prevPos.x, this.prevPos.y);

    this.updatePrev();

  }

​

  updatePrev() {

    this.prevPos.x = this.pos.x;

    this.prevPos.y = this.pos.y;

  }

​

  edges() {

    if (this.pos.x > width) this.pos.x = 0;

    if (this.pos.x < 0) this.pos.x = width;

    if (this.pos.y > height) this.pos.y = 0;

    if (this.pos.y < 0) this.pos.y = height;

  }

}