Multi-touch Scale Stage

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Note: This lab only works on devices that support multi-touch gestures such as iOS because it makes use of multiple touch events.

Instructions: Using a mobile device that supports multi-touch gestures such as iOS, use two fingers to zoom in or out of the stage

Konva Multi-touch Scale Stageview raw
<!DOCTYPE html>
<html>
  <head>
    <script src="https://unpkg.com/konva@4.0.18/konva.min.js"></script>
    <meta charset="utf-8" />
    <title>Konva Multi-touch Scale Stage 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 lastDist = 0;
      var startScale = 1;

      function getDistance(p1, p2) {
        return Math.sqrt(Math.pow(p2.x - p1.x, 2) + Math.pow(p2.y - p1.y, 2));
      }

      var stage = new Konva.Stage({
        container: 'container',
        width: width,
        height: height,
        draggable: true,
        x: width / 2,
        y: height / 2,
        offset: {
          x: width / 2,
          y: height / 2
        }
      });

      var layer = new Konva.Layer();

      var triangle = new Konva.RegularPolygon({
        x: 190,
        y: stage.height() / 2,
        sides: 3,
        radius: 80,
        fill: 'green',
        stroke: 'black',
        strokeWidth: 4
      });

      var circle = new Konva.Circle({
        x: 380,
        y: stage.height() / 2,
        radius: 70,
        fill: 'red',
        stroke: 'black',
        strokeWidth: 4
      });

      stage.on('touchmove', function(e) {
        e.evt.preventDefault();
        var touch1 = e.evt.touches[0];
        var touch2 = e.evt.touches[1];

        if (touch1 && touch2) {
          var dist = getDistance(
            {
              x: touch1.clientX,
              y: touch1.clientY
            },
            {
              x: touch2.clientX,
              y: touch2.clientY
            }
          );

          if (!lastDist) {
            lastDist = dist;
          }

          var scale = (stage.scaleX() * dist) / lastDist;

          stage.scaleX(scale);
          stage.scaleY(scale);
          stage.batchDraw();
          lastDist = dist;
        }
      });

      stage.on('touchend', function() {
        lastDist = 0;
      });

      layer.add(triangle);
      layer.add(circle);
      stage.add(layer);
    </script>
  </body>
</html>
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