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How to straighten a rotated 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.
We can straighten a rotated Polygon object by using the straighten method. The straighten method straightens an object by rotating it from its current angle to 0, 90,180 or 270 etc., depending on the angle that is closer.
Syntax
straighten(): fabric.Object
Example 1: Passing the Angle Property a Value without using the straighten Method
Let’s see a code example to see how our Polygon object looks when the straighten method is not used. The angle property sets the angle of rotation of an object in degrees. Here, we have specified the angle as 45. But since we have not applied the straighten property, the angle of rotation will remain as 45 degrees.
<!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>
Passing the angle property a value without using the straighten method
</h2>
<p>You can see that the polygon has an angle of 45 degrees</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 polygon object
var polygon = new fabric.Polygon(
[
{ x: -20, y: -35 },
{ x: 20, y: -35 },
{ x: 40, y: 0 },
{ x: 20, y: 35 },
{ x: -20, y: 35 },
{ x: -40, y: 0 },
],
{
stroke: "red",
left: 100,
top: 50,
fill: "black",
strokeWidth: 2,
strokeLineJoin: "bevil",
angle: 45,
}
);
// Adding it to the canvas
canvas.add(polygon);
</script>
</body>
</html>
Example 2: Using the straighten Method
Let’s see a code example to see how the Polygon object looks like when the straighten method is used in conjunction with the angle property. Although we have set the angle of rotation as 45 degrees, our polygon object will be straightened by rotating it back to 0 degree as we have used the straighten 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>Using the straighten method</h2>
<p>
You can see that the angle of rotation is 0 degree for the polygon object
</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 polygon object
var polygon = new fabric.Polygon(
[
{ x: -20, y: -35 },
{ x: 20, y: -35 },
{ x: 40, y: 0 },
{ x: 20, y: 35 },
{ x: -20, y: 35 },
{ x: -40, y: 0 },
],
{
stroke: "red",
left: 100,
top: 50,
fill: "black",
strokeWidth: 2,
strokeLineJoin: "bevil",
angle: 45,
}
);
// Adding it to the canvas
canvas.add(polygon);
// Using the straighten method
polygon.straighten();
</script>
</body>
</html>
Conclusion
In this tutorial, we used two simple examples to demonstrate how you can straighten a rotated Polygon object using FabricJS.
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