// 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;

let iterationsPerLoop = 20;

​

// Scale / resolution

let stepSize = 5;

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(500, 500);

​

  // 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(300);

  spiral();

}

​

function spiral() {

  let r = 0;

  let g = 0;

  let b = 0;

  while (true) {

    for(i = 0; i < iterationsPerLoop; i++) {

          // If prime draw circle

      r=random(1,255);

      g=random(1,255);

      b=random(1,255);

      stroke(r,g,b)

      fill(r,g,b);

      if (isPrime(step)) {

        stroke(r,g,b);

        fill(r,g,b);

        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) {

        break;

    }

    }

  }

}