Drawing Spirographs

HTML5 canvas demo.

by Alan November

HTML

<canvas id="myCanvas" width="300" height="300" />

JavaScript

$(document).ready(function() {
    //From https://developer.mozilla.org/samples/
    //canvas-tutorial/5_2_canvas_translate.html

    draw();        
});

function draw() {
  var ctx = document.getElementById('myCanvas').getContext('2d');
  ctx.fillRect(0,0,300,300);
  for (i=0;i<3;i++) {
    for (j=0;j<3;j++) {
      ctx.save();
      ctx.strokeStyle = "#9CFF00";
      ctx.translate(50+j*100,50+i*50);
      drawSpirograph(ctx,20*(j+2)/(j+1),-8*(i+3)/(i+1),5);
      ctx.restore();
    }
  }
}

function drawSpirograph(ctx,R,r,O){
  var x1 = R-O;
  var y1 = 0;
  var i  = 1;
  ctx.beginPath();
  ctx.moveTo(x1,y1);
  do {
    if (i>20000) break;
    var x2 = (R+r)*Math.cos(i*Math.PI/72) - 
             (r+O)*Math.cos(((R+r)/r)*(i*Math.PI/72))
    var y2 = (R+r)*Math.sin(i*Math.PI/72) - 
             (r+O)*Math.sin(((R+r)/r)*(i*Math.PI/72))
    ctx.lineTo(x2,y2);
    x1 = x2;
    y1 = y2;
    i++;
  } while (x2 != R-O && y2 != 0 );
  ctx.stroke();
}