Center Scale

<!DOCTYPE html>
<html>

<head>
  <script src="https://cdn.rawgit.com/konvajs/konva/1.1.1/konva.min.js"></script>
  <meta charset="utf-8">
  <title>Konva Image Demo</title>
  <style>
    body {
      margin: 0;
      padding: 0;
      overflow: hidden;
      background-color: #F0F0F0;
    }
  </style>
</head>

<body>
  <div id="container"></div>
  <script>
    var width = window.innerWidth;
    var height = window.innerHeight;

    var stage = new Konva.Stage({
      container: 'container',
      width: width,
      height: height
    });

    var layer = new Konva.Layer();
    var imageObj = new Image();
    imageObj.onload = function() {

      var yoda = new Konva.Image({
        x: 50,
        y: 50,
        image: imageObj,
        width: 106,
        height: 118,
        draggable: true
      });

      // add the shape to the layer
      layer.add(yoda);

      //setting the offset to center
      //but don't know why it's moving the image.
      yoda.setOffset({
        x: yoda.width() / 2,
        y: yoda.height() / 2
      });
      // setting it's position back to original
      // position but don't know why I need to
      // adding the offset values
      yoda.position({
        x: 50 + yoda.width() / 2,
        y: 50 + yoda.height() / 2
      });

      //center point
      layer.add(new Konva.Circle({
        x: 50 + yoda.width() / 2,
        y: 50 + yoda.height() / 2,
        fill: 'red',
        radius: 2
      }));

      // add the layer to the stage
      stage.add(layer);

      setTimeout(function() {
        yoda.scale({
          x: 0.5,
          y: 0.5
        });
        layer.draw();
      }, 3000);
    };
    imageObj.src = 'http://konvajs.github.io/assets/yoda.jpg';
  </script>

</body>

</html>

// Code goes here

/* Styles go here */