let x = 0,

  y = 0,

  prevx,

  prevy;

let angle = 0;

let radius = 0;

let theta = 0;

let osc = [];

let env = [];

let notes = [41, 45, 48, 52, 53, 57, 60, 64, 65]; // Midi note numbers

// F A C E F A C E in two octaves if you want to play along

​

function setup() {

  console.log("Start");

​

  createCanvas(400, 400);

  stroke(255);

  background(0);

  x = width / 2;

  y = height / 2;

  prevx = width / 2;

  prevy = height / 2;

​

  // Start the tone oscillators and envelopes

  for (let i = 0; i <= 10; i++) {

    if (i < 5) osc[i] = new p5.TriOsc();

    else osc[i] = new p5.SinOsc();

​

    osc[i].start();

    osc[i].amp(0);

​

    env[i] = new p5.Envelope(0.1, 0.7, 2, 0.1);

  }

}

​

function playNote(note, duration, oscNum) {

  osc[oscNum].freq(midiToFreq(note));

  env[oscNum].play(osc[oscNum]);

}

​

function drawLine() {

  // draws the sweeping line

  let x = width / 2;

  let y = height / 2;

​

  for (i = 0; i < width * 0.7; i += 4) {

    let posx = x + cos(theta) * i;

    let posy = y + sin(theta) * i;

​

    let col = get(posx, posy);

​

    if (red(col) == 255 && green(col) == 255 && blue(col) == 0) {

      //work out length of line

      let length = sqrt((posx - x) * (posx - x) + (posy - y) * (posy - y));

      let note = floor(map(length, 0, width / 2, 1, 8));

​

      if (note != 1) playNote(notes[note], 20, note);

    }

    point(posx, posy);

  }

  theta += 0.002;

}

​

function drawSpiral() {

  // draws the spiral with the prime dots

  while (x < width || y < height) {

    x = width / 2 + cos(angle) * radius;

    y = height / 2 + sin(angle) * radius;

​

    line(x, y, prevx, prevy);

​

    prevx = x;

    prevy = y;

​

    if (isPrime(step)) {

      fill(255, 255, 0);

      noStroke();

      circle(x, y, 5);

      fill(255, 255, 255);

      stroke(255, 255, 255);

    }

​

    step++;

    angle += 0.1;

    radius += 0.5;

  }

​

  angle = 0;

  radius = 0;

  prevx = width / 2;

  prevy = height / 2;

  step = 0;

  x = width / 2;

  y = height / 2;

}

​

function draw() {

  background(0);

  drawSpiral();

  drawLine();

}

​

// Function to test if number is prime - From D Shiffman Ulam Spiral

function isPrime(value) {

  if (value == 1) return false;

  for (let i = 2; i <= sqrt(value); i++) {

    if (value % i == 0) {

      return false;

    }

  }

  return true;

}

​