SpiroGraph

by Mike Kerney

HTML

<button onclick="doDrawing();">Start Drawing</button>

<canvas id="myCanvas" width="400" height="400" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>

JavaScript

var t = 0;
var c = document.getElementById("myCanvas");
var R =c.width / 6;
var ctx = c.getContext("2d");




function doDrawing() {
t=0;
  ctx.clear();
var r =Math.floor(Math.random() * R);
var O = Math.floor(Math.random() * 20);
  var run = 0;
  var x= 200+((R+r)*Math.cos(t) - (r+O)*Math.cos(((R+r)/r)*t));
  var y = 200+((R+r)*Math.sin(t) - (r+O)*Math.sin(((R+r)/r)*t));


  

    
    var color = '#' + Math.floor(Math.random() * 16777215).toString(16);


    // Start the Drawing
    ctx.beginPath();
    ctx.strokeStyle = color;
    ctx.moveTo(x, y);

    //Use the timer to create drawing
    var interval = setInterval(function () {
       run += 1;
        if (run ===1000) {
            clearInterval(interval);
        }

        drawCircle(r,O);
    },2);

}

function drawCircle(r,O) {
    t += .03;

   x = Math.floor(200+(R+r)*Math.cos(t) - (r+O)*Math.cos(((R+r)/r)*t));
  y = Math.floor(200+(R+r)*Math.sin(t) - (r+O)*Math.sin(((R+r)/r)*t));



    ctx.lineTo(x, y) ;
    ctx.stroke();
}

CanvasRenderingContext2D.prototype.clear = CanvasRenderingContext2D.prototype.clear || function (preserveTransform) {
    if (preserveTransform) {
        this.save();
        this.setTransform(1, 0, 0, 1, 0, 0);
    }

    this.clearRect(0, 0, this.canvas.width, this.canvas.height);

    if (preserveTransform) {
        this.restore();
    }
};