new.html


<!DOCTYPE html>
<html>
<head>
    <script src="https://cdn.rawgit.com/konvajs/konva/1.6.3/konva.min.js"></script>
    <meta charset="utf-8">
    <title>Konva Zoom Relative to 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 stage = new Konva.Stage({
        container: 'container',
        width: width,
        height: height
    });
    var layer = new Konva.Layer();
    stage.add(layer);
    layer.add(new Konva.Circle({
        x: stage.width() / 2,
        y: stage.height() / 2,
        radius: 50,
        fill: 'red'
    }));
    var circle = new Konva.Circle({
        x: stage.width() / 2,
        y: stage.height() / 2,
        radius: 50,
        fill: 'green'
    });
    layer.add(circle);
    layer.draw();
    var scaleBy = 1.01;
    window.addEventListener('wheel', function(e){
        e.preventDefault();
    var oldScale = stage.scaleX();
    var mousePointTo = {
        x: stage.getPointerPosition().x / oldScale - stage.x() / oldScale,
        y: stage.getPointerPosition().y / oldScale - stage.y() / oldScale,
    };
    var newScale = e.deltaY > 0 ? oldScale * scaleBy : oldScale / scaleBy;
    stage.scale({ x: newScale, y: newScale });
    var newPos = {
        x: -(mousePointTo.x - stage.getPointerPosition().x / newScale) * newScale,
        y: -(mousePointTo.y - stage.getPointerPosition().y / newScale) * newScale
    };
    stage.position(newPos);
    stage.batchDraw();
    });
</script>
</body>
</html>