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How to draw an octagon 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. Specifying the array of points is crucial without which our polygon object would not be rendered onto the canvas. We can also customize the polygon object by using various properties. 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 an Octagon using Polygon
Let's see a code example to see how we draw an octagon using polygon. An octagon is a polygon which has 8 sides and 8 angles. Although many types of octagon can be drawn, in this example we will demonstrate how to draw a regular octagon where all the sides are equal in length.
<!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 an octagon using Polygon</h2>
<p>You can see an octagon 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
var octagon = new fabric.Polygon(
[
{ x: -37.282, y: 90 },
{ x: 37.282, y: 90 },
{ x: 90, y: 37.282 },
{ x: 90, y: -37.282 },
{ x: 37.282, y: -90 },
{ x: -37.282, y: -90 },
{ x: -90, y: -37.282 },
{ x: -90, y: 37.282 },
],
{
stroke: "red",
left: 110,
top: 10,
strokeWidth: 2,
strokeLineJoin: "bevel",
}
);
// Adding it to the canvas
canvas.add(octagon);
</script>
</body>
</html>
Understanding Octagon Coordinates
The octagon coordinates in Example 2 are calculated for a regular octagon with radius 90 pixels. Each point is positioned at 45-degree intervals around a circle, creating 8 equal sides. The coordinates use mathematical calculations where each point is at distance 90 from the center, with alternating positions at ±37.282 and ±90.
Key Properties for Polygon Customization
- fill - Sets the interior color of the polygon
- stroke - Defines the border color
- strokeWidth - Controls border thickness
- strokeLineJoin - Sets how line segments connect (bevel, round, miter)
- left, top - Position the polygon on the canvas
Conclusion
In this tutorial, we demonstrated how to draw an octagon with Polygon using FabricJS. The key is providing the correct array of 8 coordinate points that form a regular octagon shape, then customizing appearance with stroke and positioning properties.
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