How to set the opacity of Triangle using FabricJS?


<p>In this tutorial, we are going to learn how to set the opacity of Triangle using FabricJS. Triangle is one of the various shapes provided by FabricJS. In order to create a triangle, we will have to create an instance of <em>fabric.Triangle</em> class and add it to the canvas. We can customize a triangle object by adding a fill colour to it, eliminate its borders or even make changes in its dimensions. Similarly we can also change its opacity by using the <em>opacity</em> property.</p><h2>Syntax</h2><pre class="just-code notranslate language-javascript" data-lang="javascript">new fabric.Triangle({ opacity: Number }: Object)</pre><h2>Parameters</h2><ul class="list"><li><p><strong>Options</strong><strong> (optional)</strong> − This parameter is an <em>Object</em> which provides additional customizations to our Triangle. Using this parameter colour, cursor, border width and a lot of other properties can be changed related to the object of which <em>opacity</em> is a property.</p></li></ul><h2>Options Keys</h2><ul class="list"><li><p><strong>opacity</strong><strong> </strong>− This property accepts a <strong>Number</strong> as value which allows us to control the opacity of an object. The default value of opacity property is 1.</p></li></ul><h2>Example 1</h2><p><strong>Default appearance of a Triangle object</strong></p><p>Let's see a code example to see how our Triangle object looks like with the default value of <em>opacity</em> property. We will not pass any opacity key to the class, as shown in the example below −</p><pre class="demo-code notranslate language-javascript" data-lang="javascript"><!DOCTYPE html> <html> <head>    <!-- Adding the Fabric JS Library-->    <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/510/fabric.min.js"></script> </head> <body>    <h2>Default appearance of a Triangle object</h2>    <p>Notice that the triangle is fully opaque.</p>    <canvas id="canvas"></canvas>    <script>       // Initiate a canvas instance       var canvas = new fabric.Canvas("canvas");       canvas.setWidth(document.body.scrollWidth);       canvas.setHeight(250);       // Initiate a triangle object       var triangle = new fabric.Triangle({          left: 105,          top: 70,          width: 90,          height: 80,          fill: "#746cc0",          stroke: "#967bb6",          strokeWidth: 5,       });       // Add it to the canvas       canvas.add(triangle);    </script> </body> </html></pre><h2>Example 2</h2><p><strong>Passing the <em>opacity</em> property as key</strong></p><p>In this example, we will see how assigning a value to the <em>opacity</em> property changes the opacity of the triangle object in our canvas. Here we have used 0.3 as opacity which thus makes our triangle object look translucent instead of fully opaque.</p><pre class="demo-code notranslate language-javascript" data-lang="javascript"><!DOCTYPE html> <html> <head>    <!-- Adding the Fabric JS Library-->    <script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/510/fabric.min.js"></script> </head> <body>    <h2>Passing the opacity property as key</h2>    <p>You can see our triangle is not fully opaque</p>    <canvas id="canvas"></canvas>    <script>       // Initiate a canvas instance       var canvas = new fabric.Canvas("canvas");       canvas.setWidth(document.body.scrollWidth);       canvas.setHeight(250);       // Initiate a triangle object       var triangle = new fabric.Triangle({          left: 105,          top: 70,          width: 90,          height: 80,          fill: "#746cc0",          stroke: "#967bb6",          strokeWidth: 5,          opacity: 0.3,       });       // Add it to the canvas       canvas.add(triangle);    </script> </body> </html></pre>

Updated on: 27-Jun-2022

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