bonsaijs text positioning

HTML

<script type="text/javascript" src="//cdnjs.cloudflare.com/ajax/libs/bonsai/0.4.3/bonsai.min.js"></script>

<div id="movie"></div>

JavaScript

bonsai.run(document.getElementById('movie'), {
  code: function() {
  
		function getRandomArbitrary(min, max) {
  		return Math.random() * (max - min) + min;
		};

		function rgbaColor(red, green, blue, opac) {
			return 'rgba(' + red + ',' + green + ',' + blue + ',' + opac + ')';
		};
  
  	var w = stage.options.width;
    //var h = stage.options.heigh;
    
    var circles = [];
  
		for (var i = 0; i < 800; i++) {
    	var centerW = getRandomArbitrary(0, w);
      var centerH = getRandomArbitrary(0, 500);
      var radius = getRandomArbitrary(0, (Math.random() * 100));
      
     	var r = getRandomArbitrary(0, 255);
      var g = getRandomArbitrary(0, 255);
      var b = getRandomArbitrary(0, 255);
      var opac = getRandomArbitrary(0.5, 0.8);
      var color = rgbaColor(r, g, b, opac);

			var circle = new Circle(centerW, centerH, radius);
    	circles.push(circle);
      circle.fill(color).addTo(stage);
    }
   	
    stage.on('pointermove', function(e) {
    	mouseX = e.x;
      mouseY = e.y;
      
			console.log("Maus bewegen, Maus bewegen" + e.x + " " + e.y);
  	});
  },
  width: 500,
  height: 500
});