Fabric.js | Circle borderOpacityWhenMoving Property

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

To make it possible, we are going to use a JavaScript library called FabricJS. After importing the library using CDN, we will create a canvas block in the body tag that will contain our circle. After this, we will initialize instances of Canvas and Circle provided by FabricJS and change border opacity while moving the circle using borderOpacityWhenMoving property and render the Circle on the Canvas as given in the below example.

Syntax:

fabric.Circle({
    radius: number,
    borderOpacityWhenMoving: number
}); 

Parameters: This function accept two parameters as mentioned above and described below:

  • radius: It specifies the radius of circle.
  • borderOpacityWhenMoving: It specifies the opacity of border while it is moving. Default value is 0.4.

Example: This example uses FabricJS to change border opacity while moving a canvas circle. Note that you have to click on the object to see the border.

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<!DOCTYPE html>
<html>
  
<head>
    <title>
        Fabric.js | Circle borderOpacityWhenMoving Property
    </title>
  
    <!-- FabricJS CDN -->
    <script src=
    </script>
</head>
  
<body>
    <center>
        <h1 style="Color: green;">
            GeeksforGeeks
        </h1>
  
        <b>
            Change border opacity while moving 
            a canvas circle using FabricJS.
        </b>
  
        <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 Circle instance
            var circle = new fabric.Circle({
                radius: 50,
                borderOpacityWhenMoving: 1
            });
  
            // Render the circle in canvas
            canvas.add(circle);
        </script>
    </center>
</body>
  
</html>

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Output:

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