// author: Winston Smith, @sequentialchaos

// created: Oct. 27, 2019

// web editor: https://editor.p5js.org/sequentialchaos/sketches/R3G_dBXzc

//

// fork of: 

//   https://editor.p5js.org/codingtrain/sketches/XjLDE7gu6

//   by Daniel Shiffman

//   https://thecodingtrain.com/CodingInTheCabana/002-collatz-conjecture.html

//   https://youtu.be/EYLWxwo1Ed8

​

let start = 1;

let reset = start;

let angle = 0.13; // changed from 0.15

let inc = 300;

let len;

let sw;

​

function setup() {

  createCanvas(innerWidth, innerHeight);

  background(0);

  colorMode(HSB, 1, 1, 1, 1);

  let minDimension = min(width, height)

  sw = map(minDimension, 300, 1000, 2, 7)

  strokeWeight(sw); // changed from 2

  len = map(minDimension, 300, 1000, 3, 8) // changed from 5

}

​

function draw() {

  let sequence = [];

  let n = start;

  do {

    sequence.push(n);

    n = collatz(n);

  } while (n != 1);

  sequence.push(1);

  sequence.reverse();

​

  resetMatrix();

  translate(width / 2, height);

  for (let j = 0; j < sequence.length; j++) {

    let value = sequence[j];

    if (value % 2 == 0) {

      rotate(angle);

    } else {

      rotate(-angle);

    }

    stroke(j / sequence.length, 1, 1, 0.03); // alpha changed from 0.04

    line(0, 0, 0, -len);

    translate(0, -len);

  }

  start += inc;

​

  // reset the starting number before it gets too large

  if (start > 50000) {

    reset++

    start = reset

  }

}

​

function collatz(n) {

  // even

  if (n % 2 == 0) {

    return n / 2;

    // odd

  } else {

    return (n * 3 + 1) / 2;

  }

}