HTML5 Canvas Clipping Functions Tuturial

To draw things inside of clipping regions with Konva, we can set the clip
property of any container, including a group, a layer, or the stage.
Clipping regions are defined by an x, y, width, and height. In this tutorial,
we’ll draw blobs inside of a rectangular clipping region applied to a group.

Konva Clipping Functions Demoview raw

<!DOCTYPE html>
<html>
<head>
  <script src="https://cdn.rawgit.com/konvajs/konva/2.0.2/konva.min.js"></script>
  <meta charset="utf-8">
  <title>Konva Clipping Function 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 group = new Konva.Group({
        clipFunc: function(ctx) {
          ctx.arc(250, 120, 50, 0, Math.PI * 2, false);
          ctx.arc(150, 120, 60, 0, Math.PI * 2, false);
        },
        draggable: true
    });

    var blueBlob = new Konva.Line({
        points: [73, 140, 340, 23, 500, 109, 300, 170],
        stroke: 'blue',
        strokeWidth: 10,
        fill: '#aaf',
        tension: 0.8,
        closed : true
    });

    var redBlob = new Konva.Line({
        points: [73, 140, 340, 23, 500, 109],
        stroke: 'red',
        strokeWidth: 10,
        fill: '#faa',
        tension: 1.2,
        scale: {x : 0.5, y : 0.5},
        x: 100,
        y: 50,
        closed : true
    });

    group.add(blueBlob);
    group.add(redBlob);
    layer.add(group);

    // add the layer to the stage
    stage.add(layer);
  </script>

</body>
</html>