FabricJS - Clip object to bounding box

How to use a rect as a bounding box for an image or text to allow for a clipping region or bounding box.

by Eugene Vilder

HTML

<script src="//cdnjs.cloudflare.com/ajax/libs/lodash.js/1.2.1/lodash.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/fabric.js/1.4.8/fabric.min.js"></script>
<script src="http://promincproductions.com/gaTrackingJSFiddle.js"></script>
<canvas id="c" width="400" height="400"></canvas>

CSS

#c {
    border:0px solid #ccc;
}

JavaScript

var img01URL = 'https://www.google.com/images/srpr/logo4w.png';
var img02URL = 'http://fabricjs.com/lib/pug.jpg';

var canvas = new fabric.Canvas('c');

// Note the use of the `originX` and `originY` properties, which we set
// to 'left' and 'top', respectively. This makes the math in the `clipTo`
// functions a little bit more straight-forward.
var clipRect1 = new fabric.Rect({
    originX: 'left',
    originY: 'top',
    left: 180,
    top: 10,
    width: 200,
    height: 200,
    fill: '#DDD', /* use transparent for no fill */
    strokeWidth: 0,
    selectable: true
});
// We give these `Rect` objects a name property so the `clipTo` functions can
// find the one by which they want to be clipped.
clipRect1.set({
    clipFor: 'pug'
});
canvas.add(clipRect1);

var clipRect2 = new fabric.Rect({
    originX: 'left',
    originY: 'top',
    left: 10,
    top: 10,
    width: 150,
    height: 150,
    fill: '#DDD', /* use transparent for no fill */
    strokeWidth: 0,
    selectable: false
});
// We give these `Rect` objects a name property so the `clipTo` functions can
// find the one by which they want to be clipped.
clipRect2.set({
    clipFor: 'logo'
});
canvas.add(clipRect2);

function findByClipName(name) {
    return _(canvas.getObjects()).where({
            clipFor: name
        }).first()
}

// Since the `angle` property of the Image object is stored 
// in degrees, we'll use this to convert it to radians.
function degToRad(degrees) {
    return degrees * (Math.PI / 180);
}

var clipByName = function (ctx) {
    this.setCoords();
    var clipRect = findByClipName(this.clipName);
    var scaleXTo1 = (1 / this.scaleX);
    var scaleYTo1 = (1 / this.scaleY);
    ctx.save();
    
    var ctxLeft = -( this.width / 2 ) + clipRect.strokeWidth;
		var ctxTop = -( this.height / 2 ) + clipRect.strokeWidth;
		var ctxWidth = clipRect.width - clipRect.strokeWidth;
		var ctxHeight = clipRect.height - clipRect.strokeWidth;

    ctx.translate( ctxLeft, ctxTop );
    
   ...