Prevent Fabric js Objects from scaling out of the canvas boundary
You can set on object modified listener and check if object is out of bounds. If so, then restore it to its original state.
this.canvas.on('object:modified', function (options: any) {
let obj = options.target;
let boundingRect = obj.getBoundingRect(true);
if (boundingRect.left < 0
|| boundingRect.top < 0
|| boundingRect.left + boundingRect.width > scope.canvas.getWidth()
|| boundingRect.top + boundingRect.height > scope.canvas.getHeight()) {
obj.top = obj._stateProperties.top;
obj.left = obj._stateProperties.left;
obj.angle = obj._stateProperties.angle;
obj.scaleX = obj._stateProperties.scaleX;
obj.scaleY = obj._stateProperties.scaleY;
obj.setCoords();
obj.saveState();
}
});
I was able to solve the problem as follows:
var canvas = new fabric.Canvas('canvas');
canvas.add(new fabric.Circle({ radius: 30, fill: '#f55', top: 100, left: 100 }));
canvas.item(0).set({
borderColor: 'gray',
cornerColor: 'black',
cornerSize: 12,
transparentCorners: true
});
canvas.setActiveObject(canvas.item(0));
canvas.renderAll();
canvas.on('object:moving', function (e) {
var obj = e.target;
// if object is too big ignore
if(obj.currentHeight > obj.canvas.height || obj.currentWidth > obj.canvas.width){
return;
}
obj.setCoords();
// top-left corner
if(obj.getBoundingRect().top < 0 || obj.getBoundingRect().left < 0){
obj.top = Math.max(obj.top, obj.top-obj.getBoundingRect().top);
obj.left = Math.max(obj.left, obj.left-obj.getBoundingRect().left);
}
// bot-right corner
if(obj.getBoundingRect().top+obj.getBoundingRect().height > obj.canvas.height || obj.getBoundingRect().left+obj.getBoundingRect().width > obj.canvas.width){
obj.top = Math.min(obj.top, obj.canvas.height-obj.getBoundingRect().height+obj.top-obj.getBoundingRect().top);
obj.left = Math.min(obj.left, obj.canvas.width-obj.getBoundingRect().width+obj.left-obj.getBoundingRect().left);
}
});
var left1 = 0;
var top1 = 0 ;
var scale1x = 0 ;
var scale1y = 0 ;
var width1 = 0 ;
var height1 = 0 ;
canvas.on('object:scaling', function (e){
var obj = e.target;
obj.setCoords();
var brNew = obj.getBoundingRect();
if (((brNew.width+brNew.left)>=obj.canvas.width) || ((brNew.height+brNew.top)>=obj.canvas.height) || ((brNew.left<0) || (brNew.top<0))) {
obj.left = left1;
obj.top=top1;
obj.scaleX=scale1x;
obj.scaleY=scale1y;
obj.width=width1;
obj.height=height1;
}
else{
left1 =obj.left;
top1 =obj.top;
scale1x = obj.scaleX;
scale1y=obj.scaleY;
width1=obj.width;
height1=obj.height;
}
});<html>
<head>
<title>Basic usage</title>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.3/fabric.min.js"></script>
</head>
<body>
<canvas id="canvas" style= "border: 1px solid black" height= 480 width = 360></canvas>
</body>
</html>If you want to perform a real time prevention, you should use object:scaling event, as object:modified is only triggered at the end of the transformation.
1) Add event handler to canvas:
this.canvas.on('object:scaling', (e) => this._handleScaling(e));
2) In the handler function, get the old and the new object's bounding rect:
_handleScaling(e) {
var obj = e.target;
var brOld = obj.getBoundingRect();
obj.setCoords();
var brNew = obj.getBoundingRect();
3) For each border, check if object has scaled beyond the canvas boundaries and compute its left, top and scale properties:
// left border
// 1. compute the scale that sets obj.left equal 0
// 2. compute height if the same scale is applied to Y (we do not allow non-uniform scaling)
// 3. compute obj.top based on new height
if(brOld.left >= 0 && brNew.left < 0) {
let scale = (brOld.width + brOld.left) / obj.width;
let height = obj.height * scale;
let top = ((brNew.top - brOld.top) / (brNew.height - brOld.height) *
(height - brOld.height)) + brOld.top;
this._setScalingProperties(0, top, scale);
}
4) Similar code for the other borders:
// top border
if(brOld.top >= 0 && brNew.top < 0) {
let scale = (brOld.height + brOld.top) / obj.height;
let width = obj.width * scale;
let left = ((brNew.left - brOld.left) / (brNew.width - brOld.width) *
(width - brOld.width)) + brOld.left;
this._setScalingProperties(left, 0, scale);
}
// right border
if(brOld.left + brOld.width <= obj.canvas.width
&& brNew.left + brNew.width > obj.canvas.width) {
let scale = (obj.canvas.width - brOld.left) / obj.width;
let height = obj.height * scale;
let top = ((brNew.top - brOld.top) / (brNew.height - brOld.height) *
(height - brOld.height)) + brOld.top;
this._setScalingProperties(brNew.left, top, scale);
}
// bottom border
if(brOld.top + brOld.height <= obj.canvas.height
&& brNew.top + brNew.height > obj.canvas.height) {
let scale = (obj.canvas.height - brOld.top) / obj.height;
let width = obj.width * scale;
let left = ((brNew.left - brOld.left) / (brNew.width - brOld.width) *
(width - brOld.width)) + brOld.left;
this._setScalingProperties(left, brNew.top, scale);
}
5) If object's BoundingRect has crossed canvas boundaries, fix its position and scale:
if(brNew.left < 0
|| brNew.top < 0
|| brNew.left + brNew.width > obj.canvas.width
|| brNew.top + brNew.height > obj.canvas.height) {
obj.left = this.scalingProperties['left'];
obj.top = this.scalingProperties['top'];
obj.scaleX = this.scalingProperties['scale'];
obj.scaleY = this.scalingProperties['scale'];
obj.setCoords();
} else {
this.scalingProperties = null;
}
}
6) Finally, when setting the scaling properties, we have to stick with the smallest scale in case the object has crossed more than one border:
_setScalingProperties(left, top, scale) {
if(this.scalingProperties == null
|| this.scalingProperties['scale'] > scale) {
this.scalingProperties = {
'left': left,
'top': top,
'scale': scale
};
}
}