// The Coding Train / Daniel Shiffman

// https://thecodingtrain.com/CodingChallenges/167-prime-spiral.html

// https://youtu.be/a35KWEjRvc0

​

// Prime Spiral: https://editor.p5js.org/codingtrain/sketches/0Ud-XsaYb

// Number Spiral: https://editor.p5js.org/codingtrain/sketches/Zs65bV-Al

// Prime vs Random Spiral: https://editor.p5js.org/codingtrain/sketches/3np1hBlXD

// Shapes and Color: https://editor.p5js.org/codingtrain/sketches/mCvvSKpZ5

// Prime Spiral 3D: https://editor.p5js.org/codingtrain/sketches/-eX078HZ5

​

// State of spiral

let x, y;

let px, py;

let step = 1;

let state = 0;

let numSteps = 1;

let turnCounter = 1;

​

// Scale / resolution

let stepSize = 13;

let totalSteps;

​

// Function to test if number is prime

function isPrime(value) {

  if (value == 1) return false;

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

    if (value % i == 0) {

      return false;

    }

  }

  return true;

}

​

function setup() {

  createCanvas(800, 800);

​

  // set up spiral

  const cols = width / stepSize;

  const rows = height / stepSize;

  totalSteps = cols * rows;

  x = width / 2;

  y = height / 2;

  px = x;

  py = y;

  background(0);

}

​

function draw() {

  frameRate(Infinity);

  for(let i = 0; i < totalSteps/4; i++) {

    fill(noise(x) * 255, noise(x, y) * 255, noise(y) * 255);

    stroke(noise(x) * 255, noise(x, y) * 255, noise(y) * 255);

    // If prime draw circle

  if (isPrime(step)) {

    circle(x, y, stepSize * 0.5);

  }

  // Connect current to previous with a line

  line(x, y, px, py);

  px = x;

  py = y;

​

  // Move according to state

  switch (state) {

    case 0:

      x += stepSize;

      break;

    case 1:

      y -= stepSize;

      break;

    case 2:

      x -= stepSize;

      break;

    case 3:

      y += stepSize;

      break;

  }

  // Change state

  if (step % numSteps == 0) {

    state = (state + 1) % 4;

    turnCounter++;

    if (turnCounter % 2 == 0) {

      numSteps++;

    }

  }

  step++;

  // Are we done?

  if (step > totalSteps) {

    noLoop();

  }

  }

​

}

​