// Daniel Shiffman

// http://patreon.com/codingtrain

// Code for: https://youtu.be/E1B4UoSQMFw

​

// Modified by Thomas Povinelli 

​

/**

  The iterate function receives an axiom to start with and returns a JavaScript 

  generator object which repeatedly applies the given rules to the axiom. 

​

  If a letter appears in the string but not in the rules it is not altered on 

  iteration. If a letter appears in the rules, it is replaced with the given 

  replacement 

​

  Rules should always have single letter keys 

*/

function *iterate(axiom, rules) {

  let choices = Object.keys(rules);

  let pattern = `(${choices.join('|')})`;

  let regex = new RegExp(pattern, 'g');

​

  while (true) {

    yield axiom; 

    axiom = axiom.replace(regex, (match, group) => {

      let replacement = rules[group];

      return replacement || group;

    });

  } 

}

​

function turtle(sentence, angle, len) {

  background(51);

  resetMatrix();

  translate(width / 2, height);

  stroke(255, 100);

  for (var i = 0; i < sentence.length; i++) {

    var current = sentence.charAt(i);

​

    if (current == "F") {

      line(0, 0, 0, -len);

      translate(0, -len);

    } else if (current == "+") {

      rotate(angle);

    } else if (current == "-") {

      rotate(-angle)

    } else if (current == "[") {

      push();

    } else if (current == "]") {

      pop();

    }

  }

}

​

function setup() {

  createCanvas(400, 400);

  background(51);

​

  // graphical parameters

  let angle = radians(25);

  let len = 200;

​

  // L-System parameters 

  const axiom = 'F';

  let rules = {

    'F': 'FF+[+F-F-F]-[-F+F+F]', 

  }

​

  let sentence = axiom;

  let lsystem = iterate(axiom, rules);

  let button = createButton("generate");

  button.mousePressed(() => {

    len *= 0.5; 

    sentence = lsystem.next().value;

    createP(sentence);

    turtle(sentence, angle, len);

  });

}