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    <p>This can be accomplished with Fabric using the <code>clipTo</code> property, but you have to 'reverse' the transformations (scale and rotation), in the <code>clipTo</code> function.</p> <p>When you use the <code>clipTo</code> property in Fabric, the scaling and rotation are applied <em>after</em> the clipping, which means that the clipping is scaled and rotated with the image. You have to counter this by applying the exact <em>reverse</em> of the transformations in the <code>clipTo</code> property function.</p> <p>My solution involves having a <code>Fabric.Rect</code> serve as the 'placeholder' for the clip region (this has advantages because you can use Fabric to move the object around and thus the clip region.</p> <p>Please note that my solution uses the <a href="http://lodash.com/">Lo-Dash</a> utility library, particularly for <a href="http://lodash.com/docs#bind"><code>_.bind()</code></a> (see code for context).</p> <h1><a href="http://jsfiddle.net/natchiketa/gXZJf/">Example Fiddle</a></h1> <hr> <h1>Breakdown</h1> <h2>1. Initialize Fabric</h2> <p>First we want our canvas, of course:</p> <pre class="lang-js prettyprint-override"><code>var canvas = new fabric.Canvas('c'); </code></pre> <h2>2. Clip Region</h2> <pre class="lang-js prettyprint-override"><code>var clipRect1 = new fabric.Rect({ originX: 'left', originY: 'top', left: 180, top: 10, width: 200, height: 200, fill: 'none', stroke: 'black', strokeWidth: 2, selectable: false }); </code></pre> <p>We give these <code>Rect</code> objects a name property, <code>clipFor</code>, so the <code>clipTo</code> functions can find the one by which they want to be clipped:</p> <pre class="lang-js prettyprint-override"><code>clipRect1.set({ clipFor: 'pug' }); canvas.add(clipRect1); </code></pre> <p>There doesn't <em>have</em> to be an actual object for the clip region, but it makes it easier to manage, as you're able to move it around using Fabric.</p> <h2>3. Clipping Function</h2> <p>We define the function which will be used by the images' <code>clipTo</code> properties separately to avoid code duplication:</p> <p>Since the <code>angle</code> property of the Image object is stored in degrees, we'll use this to convert it to radians. </p> <pre class="lang-js prettyprint-override"><code>function degToRad(degrees) { return degrees * (Math.PI / 180); } </code></pre> <p><code>findByClipName()</code> is a convenience function, which is using <a href="http://lodash.com/">Lo-Dash</a>, to find the with the <code>clipFor</code> property for the Image object to be clipped (for example, in the image below, <code>name</code> will be <code>'pug'</code>):</p> <pre class="lang-js prettyprint-override"><code>function findByClipName(name) { return _(canvas.getObjects()).where({ clipFor: name }).first() } </code></pre> <p>And this is the part that does the work:</p> <pre class="lang-js prettyprint-override"><code>var clipByName = function (ctx) { var clipRect = findByClipName(this.clipName); var scaleXTo1 = (1 / this.scaleX); var scaleYTo1 = (1 / this.scaleY); ctx.save(); ctx.translate(0,0); ctx.rotate(degToRad(this.angle * -1)); ctx.scale(scaleXTo1, scaleYTo1); ctx.beginPath(); ctx.rect( clipRect.left - this.left, clipRect.top - this.top, clipRect.width, clipRect.height ); ctx.closePath(); ctx.restore(); } </code></pre> <p><em>NOTE</em>: <em>See below for and explanation of the use of <code>this</code> in the function above.</em></p> <h2>4. <code>fabric.Image</code> object using <code>clipByName()</code></h2> <p>Finally, the image can be instantiated and made to use the <code>clipByName</code> function like this:</p> <pre class="lang-js prettyprint-override"><code>var pugImg = new Image(); pugImg.onload = function (img) { var pug = new fabric.Image(pugImg, { angle: 45, width: 500, height: 500, left: 230, top: 170, scaleX: 0.3, scaleY: 0.3, clipName: 'pug', clipTo: function(ctx) { return _.bind(clipByName, pug)(ctx) } }); canvas.add(pug); }; pugImg.src = 'http://fabricjs.com/lib/pug.jpg'; </code></pre> <h3>What does <code>_.bind()</code> do?</h3> <p>Note that the reference is wrapped in the <a href="http://lodash.com/docs#bind"><code>_.bind()</code></a> function.</p> <p>I'm using <code>_.bind()</code> for the following two reasons:</p> <ol> <li>We need to pass a reference <code>Image</code> object to <code>clipByName()</code></li> <li>The <code>clipTo</code> property is passed the canvas context, not the object.</li> </ol> <p>Basically, <code>_.bind()</code> lets you create a version of the function that uses the object you specify as the <code>this</code> context.</p> Sources <ol> <li><a href="http://lodash.com/docs#bind">http://lodash.com/docs#bind</a></li> <li><a href="http://fabricjs.com/docs/fabric.Object.html#clipTo">http://fabricjs.com/docs/fabric.Object.html#clipTo</a></li> <li><a href="http://html5.litten.com/understanding-save-and-restore-for-the-canvas-context/">http://html5.litten.com/understanding-save-and-restore-for-the-canvas-context/</a></li> </ol>
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