HTML5 Canvas Shape Resize and Transform Limits

How to limit size changes of a shape?

To limit or change resize and transform behavior you can use boundBoxFunc property.
It works a bit similar to dragBoundFunc.

Instructions: Try to resize a shape. You will see that its width is limited to 200.

Konva Shape transform and selection Demoview raw
<!DOCTYPE html>
<html>

<head>
<!-- USE DEVELOPMENT VERSION -->
<script src="https://unpkg.com/konva@2.4.2/konva.min.js"></script>
<meta charset="utf-8">
<title>Konva Transform Limits 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);

var rect = new Konva.Rect({
x: 160,
y: 60,
width: 100,
height: 90,
fill: 'red',
name: 'rect',
stroke: 'black',
draggable: true,
});
layer.add(rect);

var MAX_WIDTH = 200;
// create new transformer
var tr = new Konva.Transformer({
boundBoxFunc: function (oldBoundBox, newBoundBox) {
// "boundBox" is an object with
// x, y, width, height and rotation properties
// transformer tool will try to fit node into that box
// "width" property here is a visible width of the object
// so it equals to rect.width() * rect.scaleX()

// the logic is simple, if new width is too big
// we will limit it
if (newBoundBox.width > MAX_WIDTH) {
newBoundBox.width = MAX_WIDTH;
}

// if width is negative, the shape will have negative scaleX, so it will be reverted
if (newBoundBox.width < -MAX_WIDTH) {
newBoundBox.width = -MAX_WIDTH;
}
return newBoundBox
}
});
layer.add(tr);
tr.attachTo(rect);
layer.draw();
</script>

</body>

</html>