How to make a star with Polygon class using FabricJS?


We can create a Polygon object by creating an instance of fabric.Polygon. A polygon object can be characterized by any closed shape consisting of a set of connected straight line segments. Since it is one of the basic elements of FabricJS, we can also easily customize it by applying properties like angle, opacity etc.

Syntax

new fabric.Polygon( points: Array, options: Object )

Parameters

  • points − This parameter accepts an Array which denotes the array of points that make up the polygon object.

  • options (optional)− This parameter is an Object which provides additional customizations to our object. Using this parameter origin, stroke width and a lot of other properties can be changed related to the Polygon object.

Example 1: Default Appearance of Polygon Object

Let’s see a code example of how we can draw any general polygon object. We need to specify an array of points where each point is an object with "x" and "y". Specifying the array of points is crucial without which our polygon object would not be rendered onto the canvas.

<!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 polygon object</h2>
   <p>You can see that a polygon object has been added to the canvas</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 polygon instance
      var polygon = new fabric.Polygon(
         [
            { x: 500, y: 20 },
            { x: 550, y: 60 },
            { x: 550, y: 200 },
            { x: 350, y: 200 },
            { x: 350, y: 60 },
            { x: 500, y: 20 },
         ],
         {
            fill: "black",
            stroke: "blue",
            strokeWidth: 2,
         }
      );
      
      // Adding it to the canvas
      canvas.add(polygon);
   </script>
</body>
</html> 

Example 2: Drawing a Star using Polygon

Let’s see a code example to understand how we can draw a star using Polygon. A star or pentagram consists of 10 isosceles triangles. The length of the unequal sides in these isosceles triangles bear a golden ratio of 1.618. We can select the coordinates in such a way that the shape forms a star as given below.

<!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>Drawing a Star using Polygon</h2>
   <p>You can see that a star object has been added to the canvas</p>
   <canvas id="canvas"></canvas>
   <script>
      
      // Initiate a canvas instance
      var canvas = new fabric.Canvas("canvas");
      canvas.setWidth(document.body.scrollWidth);
      canvas.setHeight(250);
      
      // Initiating a points array
      var points = [
         { x: 349.9, y: 75, },
         { x: 379, y: 160.9,},
         { x: 469, y: 160.9,},
         { x: 397, y: 214.9,},
         { x: 423, y: 300.9,},
         { x: 350, y: 249.9,},
         { x: 276.9, y: 301,},
         { x: 303, y: 215,},
         { x: 231, y: 161,},
         { x: 321, y: 161,},
      ];
      
      // Initiating a polygon object
      var polygon = new fabric.Polygon(points, {
         left: 100,
         top: 10,
         fill: "#D81B60", 
         strokeWidth: 4,
         stroke: "green",
         cornerColor: "blue",
      });
      
      // Adding it to the canvas
      canvas.add(polygon);
   </script>
</body>
</html>

Conclusion

In this tutorial, we used two simple examples to demonstrate how you can make a star symbol with Polygon using FabricJS.

Updated on: 02-Jan-2023

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