Turtle Graphics: Difference between revisions

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* t.forward(len); or t.fd(len);
* t.forward(len); or t.fd(len);
* t.back(len); or t.bk(len);
* t.back(len); or t.bk(len);
* t.right(angle); or t.rt(angle);
* t.right(angle); or t.rt(angle); (<math>0\leq angle \leq 360</math>)
* t.left(angle); or t.lt(angle);
* t.left(angle); or t.lt(angle);
* t.penUp();
* t.penUp();
Line 14: Line 14:
* t.hideTurtle();
* t.hideTurtle();
* t.showTurtle();
* t.showTurtle();
* t.setPenSize();
* t.setPenSize(size); (size: number)
* t.setPenColor();
* t.setPenColor(col); (col colorString, e.g. 'red' or '#ff0000')


===Snowflake and Branches Example===
===Snowflake and Branches Example===

Revision as of 17:20, 20 December 2008

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();
  • t.penDown();
  • t.clean();
  • t.setPos(x,y);
  • t.hideTurtle();
  • t.showTurtle();
  • 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.showTurtle = function() { 
                this.turtleIsHidden = false; 
            };

            turtleObj.prototype.hideTurtle = function() { 
                this.turtleIsHidden = true;
                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); };

            var brd = JXG.JSXGraph.initBoard('box', {originX: 300, originY: 300, unitX: 1, unitY: 1});
            var t = new turtleObj(brd);
 
function run() {
  brd.suspendUpdate();
  //t.hideTurtle();
  eval($('input').value);
  brd.unsuspendUpdate();
}