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How to draw a rectangle with Polygon object 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 coordinates. Specifying the array of points is crucial without which our polygon object would not be rendered onto the canvas.
Here, we have customized our polygon object by assigning fill colour, stroke colour and setting the strokeWidth to 2.
<!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 Rectangle using Polygon
Let's see a code example to see how we draw a rectangle using polygon. Since it is a rectangle, we need only four coordinates that form the corners of the rectangle. The points are defined in a clockwise or counter-clockwise order to create the rectangular shape.
<!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 Rectangle using Polygon</h2>
<p>You can see a rectangle 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 object to create rectangle
var rectangle = new fabric.Polygon(
[
{ x: -240, y: 90 },
{ x: 240, y: 90 },
{ x: 240, y: -90 },
{ x: -240, y: -90 },
],
{
stroke: "red",
left: 140,
top: 10,
strokeWidth: 2,
strokeLineJoin: "bevil",
fill: "transparent"
}
);
// Adding it to the canvas
canvas.add(rectangle);
</script>
</body>
</html>
Key Points
-
To create a rectangle using Polygon, define exactly four corner points
-
The coordinates should form a rectangular shape when connected
-
Use properties like
stroke,fill, andstrokeWidthto customize appearance -
The
leftandtopproperties control the position of the polygon on the canvas
Conclusion
In this tutorial, we demonstrated how to draw a rectangle using FabricJS Polygon object. By defining four corner points, you can easily create rectangular shapes with customizable styling properties.
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