Fabric.js Polygon borderOpacityWhenMoving Property

Last Updated : 31 Aug, 2020

In this article, we are going to see how to draw a canvas polygon in which border opacity will change when the user is moving the polygon using FabricJS. The canvas polygon means the polygon is movable and can be stretched according to requirement. Further, the polygon can be customized when it comes to initial stroke color, shape, fill, or stroke width.

To make this possible we are going to use a JavaScript library called FabricJS. After importing the library, we will create a canvas block in the body tag which will contain the polygon. After this, we will initialize instances of Canvas and polygon provided by FabricJS and enable the borderOpacityWhenMoving of canvas polygon using borderOpacityWhenMoving property and render the polygon on the Canvas as given below.

Syntax:

fabric.Polygon([ 
    { x: pixel, y: pixel }, 
    { x: pixel, y: pixel }, 
    { x: pixel, y: pixel}, 
    { x: pixel, y: pixel}, 
    { x: pixel, y: pixel }],
    {
        borderOpacityWhenMoving: number
    }
);

Parameter: This property accepts a single parameter as mentioned above and described below:

borderOpacityWhenMoving: This parameter defines the border opacity of the polygon.

Note: Dimension pixels is must to create a polygon.

Below examples illustrate the Fabric.JS Polygon borderOpacityWhenMoving property in JavaScript:

Example 1:

HTML

<!DOCTYPE html>  
<html>  
  
<head>  
    <!-- Loading the FabricJS library -->
    <script src=  
"https://cdnjs.cloudflare.com/ajax/libs/fabric.js/3.6.2/fabric.min.js">  
    </script>  
</head>  
  
<body>  
    <div style="text-align: center;width: 600px;">  
        <h1 style="color: green;">  
            GeeksforGeeks  
        </h1>  
        <b>  
            Fabric.js | Polygon borderOpacityWhenMoving Property  
        </b>  
    </div>  
  
    <canvas id="canvas"
            width="600"
            height="200"
            style="border:1px solid #000000;">  
    </canvas>  
  
    <script>  
  
        // Initiate a Canvas instance  
        var canvas = new fabric.Canvas("canvas");  
  
        // Initiate a polygon instance  
        var polygon = new fabric.Polygon([  
        { x: 295, y: 10 },  
        { x: 235, y: 198 },  
        { x: 385, y: 78},  
        { x: 205, y: 78},  
        { x: 355, y: 198 }], {  
            fill: 'yellow', 
            borderOpacityWhenMoving: 0.1 
        });  
  
        // Render the polygon in canvas  
        canvas.add(polygon);  
    </script>  
</body>  
  
</html>

Output:

Example 2:

HTML

<!DOCTYPE html>  
<html>  
  
<head>  
    <!-- Loading the FabricJS library -->
    <script src=  
"https://cdnjs.cloudflare.com/ajax/libs/fabric.js/3.6.2/fabric.min.js">  
    </script>  
</head>  
  
<body>  
    <div style="text-align: center;width: 600px;">  
        <h1 style="color: green;">  
            GeeksforGeeks  
        </h1>  
        <b>  
            Fabric.js | Polygon borderOpacityWhenMoving Property  
        </b>  
    </div>  
  
    <canvas id="canvas"
            width="600"
            height="200"
            style="border:1px solid #000000;">  
    </canvas>  
  
    <script>  
  
        // Initiate a Canvas instance  
        var canvas = new fabric.Canvas("canvas");  
  
        // Initiate a polygon instance  
        var polygon = new fabric.Polygon([  
        { x: 295, y: 10 },  
        { x: 235, y: 198 },  
        { x: 385, y: 78},  
        { x: 205, y: 78},  
        { x: 355, y: 198 }], {  
            fill: 'yellow', 
            borderOpacityWhenMoving: 1 
        });  
  
        // Render the polygon in canvas  
        canvas.add(polygon);  
    </script>  
</body>  
  
</html>