Turtle Graphics
From JSXGraph Wiki
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
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 turtleObj = function(board,attributes) {
this.turtleIsHidden = false;
this.board = board;
if (attributes==null) {
this.attributes = {
strokeColor:'#000000'
};
} else {
this.attributes = attributes;
}
this.attributes.straightFirst = false;
this.attributes.straightLast = false;
this.init();
};
turtleObj.prototype.init = function() {
this.pos = [0,0];
this.isPenDown = true;
this.dir = 90;
this.attributes.curveType = 'plot';
this.curve = this.board.createElement('curve',
[[this.pos[0]],[this.pos[1]]],this.attributes);
this.turtle = this.board.createElement('point',this.pos,{fixed:true,name:' ',visible:false});
this.turtle2 = this.board.createElement('point',[this.pos[0],this.pos[1]+20],{fixed:true,name:' ',visible:false});
this.arrow = this.board.createElement('line',[this.turtle,this.turtle2],
{lastArrow:true,strokeColor:'#ff0000',straightFirst:false,straightLast:false});
}
turtleObj.prototype.forward = function(len) {
if (len==0) { return; }
var dx = -len*Math.cos(this.dir*Math.PI/180.0);
var dy = len*Math.sin(this.dir*Math.PI/180.0);
if (!this.turtleIsHidden) {
var t = this.board.createElement('transform', [dx,dy], {type:'translate'});
t.applyOnce(this.turtle);
t.applyOnce(this.turtle2);
}
if (this.isPenDown) if (this.curve.dataX.length>=8192) {
// IE workaround
this.curve = this.board.createElement('curve',
[[this.pos[0]],[this.pos[1]]],this.attributes);
}
this.pos[0] += dx;
this.pos[1] += dy;
if (this.isPenDown) {
this.curve.dataX.push(this.pos[0]);
this.curve.dataY.push(this.pos[1]);
}
};
turtleObj.prototype.back = function(len) {
this.forward(-len);
}
turtleObj.prototype.right = function(angle) {
this.dir += angle;
if (!this.turtleIsHidden) {
var t = this.board.createElement('transform', [-angle*Math.PI/180.0,this.turtle], {type:'rotate'});
t.applyOnce(this.turtle2);
}
}
turtleObj.prototype.left = function(angle) {
this.right(-angle);
}
turtleObj.prototype.penUp = function() {
this.isPenDown = false;
}
turtleObj.prototype.penDown = function() {
this.isPenDown = true;
this.curve = this.board.createElement('curve',
[[this.pos[0]],[this.pos[1]]],this.attributes);
}
turtleObj.prototype.clean = function() {
for(var el in this.board.objects) {
this.board.removeObject(el);
}
this.init();
}
turtleObj.prototype.setPos = function(x,y) {
this.pos = [x,y];
if (!this.turtleIsHidden) {
this.turtle.setPositionDirectly(JXG.COORDS_BY_USER,x,y);
this.turtle2.setPositionDirectly(JXG.COORDS_BY_USER,x,y+20);
var t = this.board.createElement('transform',
[-(this.dir-90)*Math.PI/180.0,this.turtle], {type:'rotate'});
t.applyOnce(this.turtle2);
}
this.curve = this.board.createElement('curve',
[[this.pos[0]],[this.pos[1]]],this.attributes);
}
turtleObj.prototype.setPenSize = function(size) {
this.attributes.strokeWidth = size;
this.curve = this.board.createElement('curve',
[[this.pos[0]],[this.pos[1]]],this.attributes);
};
turtleObj.prototype.setPenColor = function(colStr) {
this.attributes.strokeColor = colStr;
this.curve = this.board.createElement('curve',
[[this.pos[0]],[this.pos[1]]],this.attributes);
};
turtleObj.prototype.showTurtle = function() {
this.turtleIsHidden = false;
this.arrow.setProperty('visible:true');
this.setPos(this.pos[0],this.pos[1]);
};
turtleObj.prototype.hideTurtle = function() {
this.turtleIsHidden = true;
this.arrow.setProperty('visible:false');
this.setPos(this.pos[0],this.pos[1]);
};
turtleObj.prototype.home= function() {
this.pos = [0,0];
this.setPos(this.pos[0],this.pos[1]);
};
turtleObj.prototype.fd = function(len) { this.forward(len); };
turtleObj.prototype.bk = function(len) { this.back(len); };
turtleObj.prototype.lt = function(angle) { this.left(angle); };
turtleObj.prototype.rt = function(angle) { this.right(angle); };
turtleObj.prototype.pu = function() { this.penUp(); };
turtleObj.prototype.pd = function() { this.penDown(); };
turtleObj.prototype.ht = function() { this.hideTurtle(); };
turtleObj.prototype.st = function() { this.showTurtle(); };
turtleObj.prototype.cs = function() { this.clean(); };
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();
}
