// 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

​

// Adding a custom shape for Ulam primes

​

let x, y;

let px, py;

let step = 1;

let stepSize = 20;

let numSteps = 1;

let state = 0;

let turnCounter = 1;

let totalSteps;

let shapeRotate;

​

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);

​

  const cols = width / stepSize;

  const rows = height / stepSize;

  totalSteps = cols * rows;

​

  x = width / 2;

  y = height / 2;

  px = x;

  py = y;

  background(65,34,52);

}

​

function draw() {

  angleMode(DEGREES);

  // textSize(stepSize);

  // textAlign(CENTER, CENTER);

  //text(step, x, y);

  noStroke();

​

  if (isPrime(step)) {

     fill(206,161,203);

    cross(step);

  }

​

  px = x;

  py = y;

​

  switch (state) {

    case 0:

      x += stepSize;

      break;

    case 1:

      y -= stepSize;

      break;

    case 2:

      x -= stepSize;

      break;

    case 3:

      y += stepSize;

      break;

  }

​

  if (step % numSteps == 0) {

    state = (state + 1) % 4;

    turnCounter++;

    if (turnCounter % 2 == 0) {

      numSteps++;

    }

  }

  step++;

​

  if (step > totalSteps) {

    noLoop();

   // saveCanvas("ulam_diagonal.png");

  }

}

​

function cross(step) {

    let r = stepSize * 0.5;

    push();

    translate(x, y);

    beginShape();

    vertex(-r, -r); //1

    vertex(-0.5*r, -r);

    vertex(0, -0.5*r); //3

    vertex(0.5*r, -r);

    vertex(r, -r); //5

    vertex(r, -0.5*r);

    vertex(0.5*r, 0); //7

     vertex(r, 0.5*r);

     vertex(r, r); //9

     vertex(0.5*r, r);

     vertex(0, 0.5*r); //11

    vertex(-0.5*r, r);

    vertex(-r, r);  //13

    vertex(-r, 0.5*r);

    vertex(-0.5*r, 0); //15

    vertex(-r, -0.5*r);

    vertex(-r,-r);

    endShape(CLOSE);

    pop();

}