I'm trying to set a simple zoom in/out functionality on a canvas. I'm using KineticJS to handle touch events and drawing in canvas, but couldn't implement the zoom. KinteicJS have a similar example, but they always zoom on the center while I'm intrested to zoom on the point between the fingers.
Thank you!
A comprehensive sample I wrote for a project showing:
- desktop zooming around mouse point using scrollwheel
- crossbrowser scrollwheel use, including firefox (using jquery.mousewheel.js)
- iPAD zooming using pinch around point between fingers
- support for iPAD orientation change and disabling safari auto zoom
- zooming one layer while keeping other layers not zoomed
- OOP javascript 'class' and proxying events to local methods
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<script src="http://d3lp1msu2r81bx.cloudfront.net/kjs/js/lib/kinetic-v4.7.4.min.js"></script>
<script src="http://code.jquery.com/jquery-1.10.2.min.js"></script>
<script src="https://rawgithub.com/brandonaaron/jquery-mousewheel/master/jquery.mousewheel.js"></script>
</head>
<body>
<div id="container"></div>
<script type='text/javascript'>
function makePos(x, y) {
return {
'x': x,
'y': y
};
}
function View() {
this.init = init;
var self = this;
var kineticStage,
kineticLayer,
kineticTextLayer,
zoomOrigin = makePos(0, 0),
zoomFactor = 1.1,
pinchLastDist, pinchStartCenter;
init();
function init() {
// disable ipad zoom to prevent safari from zooming on orientation change
$('head meta[name=viewport]').remove();
$('head').prepend('<meta name="viewport" content="user-scalable=no, width=device-width, minimum-scale=1.0 , initial-scale=1.0, maximum-scale=1.0" />');
// create stage layer and circle
kineticStage = new Kinetic.Stage({
container: 'container',
width: $(document).width() - 10,
height: $(document).height() - 10,
});
kineticLayer = new Kinetic.Layer({
draggable: true
});
var circle = new Kinetic.Circle({
x: 200,
y: 200,
radius: 50,
fill: '#00D200',
stroke: 'black',
strokeWidth: 2,
});
kineticLayer.add(circle);
kineticStage.add(kineticLayer);
kineticTextLayer = new Kinetic.Layer({});
kineticStage.add(kineticTextLayer);
// register events and proxy to methods
$(kineticStage.content).on('mousewheel', function(e) {
e.preventDefault();
var evt = e.originalEvent;
stageMouseWheel.call(self, evt.deltaY, makePos(evt.clientX, evt.clientY));
});
kineticStage.getContent().addEventListener('touchmove', function(e) {
e.preventDefault(); // prevent iPAD panning
var touch1 = e.touches[0];
var touch2 = e.touches[1];
if (touch1 && touch2) {
touch1.offsetX = touch1.pageX - $(touch1.target).offset().left;
touch1.offsetY = touch1.pageY - $(touch1.target).offset().top;
touch2.offsetX = touch2.pageX - $(touch2.target).offset().left;
touch2.offsetY = touch2.pageY - $(touch2.target).offset().top;
stagePinch.call(self, makePos(touch1.offsetX, touch1.offsetY), makePos(touch2.offsetX, touch2.offsetY));
}
}, false);
kineticStage.getContent().addEventListener('touchend', function(e) {
stageTouchEnd.call(self);
}, false);
$(window).on("orientationchange", function(event) {
window.scrollTo(0, 0); // scroll to top left on orientation change
});
editTextLayer('scrollwheel/pinch to zoom');
window.scrollTo(0, 0);
}
function zoom(newscale, center) { // zoom around center
var mx = center.x - kineticLayer.getX(),
my = center.y - kineticLayer.getY(),
oldscale = kineticLayer.getScaleX();
editTextLayer('zoom ' + newscale.toFixed(2) + ' around ' + mx.toFixed(2) + ',' + my.toFixed(2));
zoomOrigin = makePos(mx / oldscale + zoomOrigin.x - mx / newscale, my / oldscale + zoomOrigin.y - my / newscale);
kineticLayer.setOffset(zoomOrigin.x, zoomOrigin.y);
kineticLayer.setScale(newscale);
kineticLayer.draw();
}
function stageMouseWheel(factor, p) {
var oldscale = kineticLayer.getScaleX(),
newscale = oldscale * (zoomFactor - (factor < 0 ? 0.2 : 0));
zoom(newscale, p);
}
function stagePinch(p1, p2) {
var dist = Math.sqrt(Math.pow((p2.x - p1.x), 2) + Math.pow((p2.y - p1.y), 2));
if (!pinchLastDist) pinchLastDist = dist;
var newscale = kineticLayer.getScale().x * dist / pinchLastDist;
var center = makePos(Math.abs((p1.x + p2.x) / 2), Math.abs((p1.y + p2.y) / 2));
if (!pinchStartCenter) pinchStartCenter = center;
zoom(newscale, pinchStartCenter);
pinchLastDist = dist;
}
function stageTouchEnd() {
pinchLastDist = pinchStartCenter = 0;
}
function editTextLayer(text) {
var label = new Kinetic.Text({
x: 0,
y: 0,
text: text,
fontSize: 12,
fontFamily: 'Calibri',
fill: 'black'
});
kineticTextLayer.destroyChildren();
kineticTextLayer.add(label);
kineticTextLayer.drawScene();
}
}
$(window).load(function() {
var view = new View();
});
</script>
</body>
</html>
For those who are still interested how we can do a zoom and pan with kineticJS in a canvas.
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