Transformations

• Move origin with translate(x,y). Make sure you save before.

function drawtranslate() {
    var ctx = document.getElementById('canvas').getContext('2d');
    ctx.fillRect(0,0,300,300);
      for (var i=0;i<3;i++) {
        for (var j=0;j<3;j++) {
            ctx.save();
            ctx.strokeStyle = "#9CFF00";
            ctx.translate(50+j*100,50+i*100);
            drawSpirograph(ctx,20*(j+2)/(j+1),-8*(i+3)/(i+1),10);
            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();
}

drawtranslate()

• rotate(angle)
• scale(x,y)