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/[email protected]/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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