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How to create a canvas with Polygon 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: Creating an Instance of fabric.Polygon() and Adding it to our Canvas
Let's see a code example of how we can add a polygon object to our canvas. The only required parameter is the points Array whereas the second argument is the optional options object.
<!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>
Creating an instance of fabric.Polygon() and adding it to our canvas
</h2>
<p>You can see that the polygon object has been added</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: 30, y: 50 },
{ x: 0, y: 0 },
{ x: 60, y: 0 },
];
// Initiating a polygon object
var polygon = new fabric.Polygon(points, {
left: 100,
top: 40,
fill: "#1e90ff",
strokeWidth: 4,
stroke: "green",
flipY: true,
scaleX: 2,
scaleY: 2,
});
// Adding it to the canvas
canvas.add(polygon);
</script>
</body>
</html>
Example 2: Manipulating the Polygon Object by using the Set Method
In this example, we have assigned the properties to the Polygon object by using the set method which is a setter for values. Any property related to stroke, strokeWidth, angle, scaling, rotation, etc, can be mutated by using this method.
<!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>Manipulating the Polygon object by using the set method</h2>
<p>You can see the Polygon object in canvas now with set values</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: 30, y: 50 },
{ x: 0, y: 0 },
{ x: 60, y: 0 },
];
// Initiating a polygon object
var polygon = new fabric.Polygon(points);
// Set the properties
polygon.set("stroke", "blue");
polygon.set("strokeWidth", 10);
polygon.set("flipY", true);
polygon.set("top", 50);
polygon.set("left", 100);
polygon.set("scaleX", 2);
polygon.set("scaleY", 2);
// Adding it to the canvas
canvas.add(polygon);
</script>
</body>
</html>
Common Properties
Here are some frequently used properties when working with fabric.Polygon:
| Property | Description | Example Value |
|---|---|---|
fill |
Background color of the polygon | "red", "#ff0000" |
stroke |
Border color | "blue", "#0000ff" |
strokeWidth |
Border thickness | 1, 5, 10 |
left/top |
Position on canvas | 100, 50 |
scaleX/scaleY |
Scaling factor | 1.5, 2 |
Conclusion
FabricJS makes creating polygons simple with the fabric.Polygon constructor. You can customize polygons using either the options object during creation or the set() method afterward for dynamic styling.
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