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 scaling event to demonstrate how polygonal objects react to scaling.
grammar
polygon.on(“scaling”, callbackFunction);
Example 1: Show how an object responds to zoom events
Let's look at a code example to see how a polygon object reacts when the Scale event occurs. We can scale the object by dragging any corner control. Here, when the object is scaled, the scale event will be triggered continuously.
<!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-scaling-event">Displaying how the object reacts to the scaling event</h2>
<p>
You can scale the polygon object and open the console from dev tools to see the logged output
</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: 0, y: 0 },
{ x: 0, y: 50 },
{ x: 50, y: 50 },
{ x: 50, y: 0 },
],
{
left: 100,
top: 30,
fill: "red",
stroke: "blue",
strokeWidth: 3,
objectCaching: false,
}
);
// Adding it to the canvas
canvas.add(polygon);
// Using the scaling event
polygon.on("scaling", () => {
canvas.renderAll();
console.log("The object is being scaled");
});
</script>
</body>
</html>
Example 2: Changing stroke color when zooming
Let's look at a code example to see how to change the stroke color when a zoom event occurs. We use the set method to set the polygon's stroke color to "orange". So when we scale the object, its stroke color will change to orange.
<!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-stroke-colour-when-scaling-happens">Changing the stroke colour when scaling happens</h2>
<p>
You can see that the stroke colour changes when the polygon is scaled
</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: 5,
objectCaching: false,
top: 50,
left: 30,
scaleX: 0.5,
scaleY: 0.5
}
);
// Adding it to the canvas
canvas.add(polygon);
// Using the scaling event
polygon.on("scaling", () => {
polygon.set("stroke", "orange")
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 zoom events using FabricJS.
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