Multi-touch Scale Shape

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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, drag and drop a shape by touching it and then dragging your finger across the screen, activate a shape by tapping on it, and scale an active shape by pinching the screen.

Konva Multi-touch Scale Shapeview 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 Shape 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;
      var activeShape = null;

      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,
        draggable: true,
        name: 'triangle'
      });

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

      stage.on('tap', function(evt) {
        // set active shape
        var shape = evt.target;
        activeShape =
          activeShape && activeShape.getName() === shape.getName()
            ? null
            : shape;

        // sync scene graph
        triangle.setAttrs({
          fill:
            activeShape && activeShape.getName() === triangle.getName()
              ? '#78E7FF'
              : 'green',
          stroke:
            activeShape && activeShape.getName() === triangle.getName()
              ? 'blue'
              : 'black'
        });

        circle.setAttrs({
          fill:
            activeShape && activeShape.getName() === circle.getName()
              ? '#78E7FF'
              : 'red',
          stroke:
            activeShape && activeShape.getName() === circle.getName()
              ? 'blue'
              : 'black'
        });

        layer.draw();
      });

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

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

            if (!lastDist) {
              lastDist = dist;
            }

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

            activeShape.scaleX(scale);
            activeShape.scaleY(scale);
            layer.draw();
            lastDist = dist;
          }
        },
        false
      );

      stage.getContent().addEventListener(
        'touchend',
        function() {
          lastDist = 0;
        },
        false
      );

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