We can create a Polygon object by creating an instance of fabric.Polygon. A polygon object can be characterized as 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 such as angle, opacity, etc. We use the rotating event to demonstrate how to make a polygonal object react to rotation through controls.
grammar
polygon.on(“rotating”, callbackFunction);
Example 1: Show how an object responds to rotation events
Let's look at a code example of how to make a polygon object react to rotation events. In this case, whenever we click on the polygon object and rotate it via the middle rotation control, we will see the recorded output. This is because the rotation event fires continuously as the object rotates.
<!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 id="Displaying-how-the-object-reacts-to-the-rotating-event">Displaying how the object reacts to the rotating event</h2>
<p>You can rotate the object to see the callback function fired</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: "red",
stroke: "blue",
strokeWidth: 2,
objectCaching: false,
}
);
// Adding it to the canvas
canvas.add(polygon);
// Using the rotating event
polygon.on("rotating", () => {
canvas.renderAll();
console.log("The polygon object is rotating");
});
</script>
</body>
</html>
Example 2: Changing fill color when rotation occurs
Let's look at a code example to see how to change the fill color when a rotate event occurs. We can use the middle rotation (mtr) control to rotate objects on the canvas. Here, when we rotate the polygon object using the mtr control, the fill color changes to "green".
<!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 id="Changing-the-fill-colour-when-rotate-happens">Changing the fill colour when rotate happens</h2>
<p>
You can see that the fill colour changes when the polygon is rotated
</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: "red",
stroke: "blue",
strokeWidth: 2,
objectCaching: false,
top: 50,
left: 30,
scaleX: 0.5,
scaleY: 0.5
}
);
// Adding it to the canvas
canvas.add(polygon);
// Using the rotating event
polygon.on("rotating", () => {
polygon.set("fill", "green")
canvas.renderAll();
});
</script>
</body>
</html>
in conclusion
In this tutorial, we use two simple examples to demonstrate how to make a polygon object react to rotation events using FabricJS.
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