Scaling to a fixed point in KineticJS

Question

I\'m having some problems with scaling a container to a fixed point.
In my case I\'m trying to scale (zoom) a stage to the mouse cursor.

Here is a way to do with

Answer 1

updated @juan.facorro's demo to scale shape instead of stage

jsFiddle

var ui = {
    stage: null,
    box: null,
    scale: 1,
    zoomFactor: 1.1,
    zoom: function(event) {
        event.preventDefault();
        var evt = event.originalEvent,
            mx = evt.offsetX,
            my = evt.offsetY,
            wheel = evt.wheelDelta / 120; //n or -n
        var zoom = (ui.zoomFactor - (evt.wheelDelta < 0 ? 0.2 : 0));
        var newscale = ui.scale * zoom;

        var origin = ui.box.getPosition();
        origin.x = mx - (mx - origin.x) * zoom;
        origin.y = my - (my - origin.y) * zoom;

        ui.box.setPosition(origin.x, origin.y);
        ui.box.setScale(newscale);
        ui.stage.draw();

        ui.scale *= zoom;
    }
};

$(function() {
    var width = $(document).width() - 2,
        height = $(document).height() - 5;
    var stage = ui.stage = new Kinetic.Stage({
        container: 'container',
        width: width,
        height: height
    });
    var layer = new Kinetic.Layer();
    var rectX = stage.getWidth() / 2 - 50;
    var rectY = stage.getHeight() / 2 - 25;

    var box = ui.box = new Kinetic.Circle({
        x: 100,
        y: 100,
        radius: 50,
        fill: '#00D200',
        stroke: 'black',
        strokeWidth: 2,
        draggable: true
    });

    // add cursor styling
    box.on('mouseover', function() {
        document.body.style.cursor = 'pointer';
    });
    box.on('mouseout', function() {
        document.body.style.cursor = 'default';
    });

    layer.add(box);
    stage.add(layer);

    $(stage.content).on('mousewheel', ui.zoom);
});