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CSS Base

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Add External Stylesheets/Pens

Any URL's added here will be added as <link>s in order, and before the CSS in the editor. If you link to another Pen, it will include the CSS from that Pen. If the preprocessor matches, it will attempt to combine them before processing.

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We can make npm packages available for you to use in your JavaScript. We use webpack to prepare them and make them available to import. We'll also process your JavaScript with Babel.

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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

// the output of the productions 
// will be a list of line segments
var lines = [];

// simple turtle graphic system to create these lines:
function turtle_new() {
	return {
		p: new vec2(),
		d: new vec2(1, 0),
		a: Math.PI / 3,

function turtle_copy(t) {
	return {
		p: t.p.clone(),
		d: t.d.clone(),
		a: t.a * 2/3,

function turtle_render(t, str, lines) {
	var i = 0;
	while (i <= str.length) {
		var c = str.substring(i, i+1);
		if (c == "F") {
			// add a line start-point at the turtle location:
      // move the turtle forward (make a new point):
      t.p = t.p.clone().add(t.d);
			// add the line end-point at the new turtle location:
    } else if (c == "+") {
			// turn turtle:
    } else if (c == "-") {
			// turn turtle:
		// push/pop machine:
    } else if (c == "[") {
			// create a copy of the turtle:
			var turtle1 = turtle_copy(t);
			var str1 = str.substring(i+1);
			i = i + turtle_render(turtle1, str1, lines);
    } else if (c == "]") {
			return i;
		i = i + 1;
	return i

// now the L-system:

// start pattern:
var str = "F";

// production rules:
var rules = {
	F: "F+F--F+F",

// apply production rules:
function apply_production_rules(str) {
	var res = [];
	for (var i=0; i<str.length; i++) {
		var c = str.substring(i, i+1);
		if (rules[c] !== undefined) {
    } else {
	str = res.join("");
  // and develop these into the lines:
  lines = [];
  turtle_render(turtle_new(), str, lines);
	return str;

// rendering & interaction:
turtle_render(turtle_new(), str, lines);

function mouse(e, p) {
  if (e == "down") {
    if (str.length > 1000) {
      // reset
      str = "F";
    } else {
	    str = apply_production_rules(str);

function draw() {
  // get min & max extents of the shape
  // in order to automatically scale to fit on screen
  var a = lines[0].clone();
  var b = lines[0].clone();
  for (var l of lines) {
  draw2D.translate(0.1, 0.1)
    .scale(0.8/Math.max(b[0], b[1]))
  // now draw lines:

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