Turtle Graphics

This is a very basic implementation of turtle graphics in JavaScript with JSXGraph. Here, we use SVG (on Firefox, Safari, Opera and Chrome) and VML (on Internet Explorer). CanvasTurtle does the same on browsers which support the canvas element.

List of available commands

There is a predefined turtle object t. Therefore, all commands start with t, like t.fd(100);

• t.forward(len); or t.fd(len);
• t.back(len); or t.bk(len);
• t.right(angle); or t.rt(angle); ([math]\displaystyle{ 0\leq angle \leq 360 }[/math])
• t.left(angle); or t.lt(angle);
• t.penUp(); or t.pu();
• t.penDown(); or t.pd();
• t.clearScreen(); or t.cs();
• t.clean();
• t.setPos(x,y);
• t.home();
• t.hideTurtle(); or t.ht();
• t.showTurtle(); or t.st();
• t.setPenSize(size); (size: number)
• t.setPenColor(col); (col: colorString, e.g. 'red' or '#ff0000')

Snowflake and Branches Example

function side(size, level) { if (level==0) { t.fd(size); return; } side(size/3, level-1); t.lt(60); side(size/3, level-1); t.rt(120); side(size/3, level-1); t.lt(60); side(size/3, level-1); } function snowflake(size, level) { (3).times(function() { side(size, level); t.rt(120); }); } t.clearScreen(); t.hideTurtle(); t.setPenSize(1) t.setPenColor("#000000") t.lt(30); t.setPos(0,-100); snowflake(250, 4); function branch(length, level) { if(level == 0) return t.fd(length) t.lt(45) branch(length/2, level-1) t.rt(90) branch(length/2, level-1) t.lt(45) t.bk(length) } function lbranch(length, angle, level) { t.fd(2*length) node(length, angle, level) t.bk(2*length) } function rbranch(length, angle, level) { t.fd(length) node(length, angle, level) t.bk(length) } function node(length, angle, level) { if (level == 0) return; t.lt(angle) lbranch(length, angle, level -1) t.rt(2*angle) rbranch(length, angle, level-1) t.lt(angle) } t.clearScreen() t.hideTurtle(); //branch(100,6) t.setPenSize(5) t.setPenColor("#008800") t.setPos(30, -150) lbranch(25, 20, 7)

References

• The snowflake and branches example have been adapted from the excellent CanvasTurtle

The turtle graphics code

<link rel="stylesheet" type="text/css" href="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraph.css" />
<script type="text/javascript" src="http://jsxgraph.uni-bayreuth.de/distrib/prototype.js"></script>
<script type="text/javascript" src="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraphcore.js"></script>
<div id="box" class="jxgbox" style="width:600px; height:600px;"></div>

var brd = JXG.JSXGraph.initBoard('box', {originX: 300, originY: 300, unitX: 1, unitY: 1});
var t = new turtleObj(brd);

function run(nr) {
  brd.suspendUpdate();
  eval($('input'+nr).value);
  brd.unsuspendUpdate();
}