code: function(type, pos, radius, canvas){
        var ctx = canvas.getCtx();
        ctx.beginPath();
        ctx.arc(pos.x, pos.y, radius, 0, Math.PI * 2, true);
        ctx.closePath();
        ctx[type]();
      }
docs: /*
  Method: render
  
  Renders a circle into the canvas.
  
  Parameters:
  
  type - (string) Possible options are 'fill' or 'stroke'.
  pos - (object) An *x*, *y* object with the position of the center of the circle.
  radius - (number) The radius of the circle to be rendered.
  canvas - (object) A <Canvas> instance.
  
  Example:
  (start code js)
  NodeHelper.circle.render('fill', { x: 10, y: 30 }, 30, viz.canvas);
  (end code)