View source for Hexagonal Gosper curve

For an explanation see [[L-systems]].
<html>
<form><textarea id="inputtext0" rows=15 cols=35 wrap="off" style="width:600px;">
var level = 3;
var axiom = 'XF';
var rules = {
    'F' : 'F',
    'X' : 'X+YF++YF-FX--FXFX-YF+', 
    'Y' : '-FX+YFYF++YF+FX--FX-Y', 
    '+' : '+',
    '-' : '-'
};
var symbols = { 'F':'F',
                'X':' ',
                'Y':' ',
                '+':'+',
                '-':'-',
                '[':'[',
                ']':']'
              } ;
              
var angle = 60;
var len = 500/Math.pow(3,level);
t.setPos(250,0);
</textarea><br />
<input type="button" value="run" onClick="run(0)">
<input type="button" value="clear" onClick="clearturtle(0)">
</form>
</html>
<jsxgraph width="600" height="600" box="box0">
var t;
var turtle = [];
var brd = [];
brd[0] = JXG.JSXGraph.initBoard('box0', {boundingbox: [-300, 300, 300, -300]});
turtle[0] = brd[0].create('turtle');

function expander(level,axiom,rules) {
    this.axiom = axiom;
    this.rules = rules;
    this.source = (level>1) ? new expander(level-1,axiom,rules) : (new function() {
        // Axiom:
        this.code = axiom;
        this.pos = 0;
        this.next = function() {
            if (this.pos>=this.code.length) return null;
            return this.code.charAt(this.pos++);
        }
    });
    
    this.code = '';
    this.pos = 0;
    this.next = function() {
        while (this.pos>=this.code.length) { // produce new symbols from source
            this.pos = 0;
            var pattern = this.source.next();
            if (!pattern) return null // Finished
            this.code = this.rules[pattern];
        }
        return this.code.charAt(this.pos++);
    }
}

function plotter(generator,symbols,len,angle,t,shrink) {
    for (var c; c=generator.next(); c) {
        switch(symbols[c]) {
            case 'F':
                t.fd(len);
                break;
            case 'f':
                t.penUp();
                t.fd(len);
                t.penDown();
                break;
            case '+':
                t.lt(angle);
                break;
            case '-':
                t.rt(angle);
                break;
            case '[':
                t.pushTurtle();
                len *= shrink;
                break;
            case ']':
                t.popTurtle();
                len /= shrink;
                break;
            default:
                ;
        }
    }
    return null;
  }
var shrink = 1.0;
 
function run(nr) {
  brd[nr].suspendUpdate();
  var code = document.getElementById('inputtext'+nr).value;
  if (code=='') { return; }
  t = turtle[nr];
  t.cs();
  t.hideTurtle();
  eval(code);
  var generator = new expander(level,axiom,rules);
  plotter(generator,symbols,len,angle,t,shrink);
  brd[nr].unsuspendUpdate();
}

function clearturtle(nr) {
  turtle[nr].cs();
}
</jsxgraph>

* Przemyslaw Prusinkiewicz, James Hanan: Lindenmayer Systems, Fractals, and Plants (Lecture Notes in Biomathematics). Springer-Verlag 1989, ISBN 0-387-97092-4
* [http://en.wikipedia.org/wiki/L-system http://en.wikipedia.org/wiki/L-system]

[[Category:Examples]]
[[Category:Fractals]]
[[Category:Turtle Graphics]]
[[Category:Lindenmayer systems]]