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How to randomly generate Polyline objects with a button click in FabricJS?
A polyline object can be characterised by 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 will create a program where pressing a button will randomly generate a Polyline object and add it to our canvas for us.
Syntax
new fabric.Polyline(points: Array, options: Object)
Parameters
points ? This parameter accepts an Array which denotes the array of points that make up the polyline 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 Polyline object.
Example 1: Creating an Instance of fabric.Polyline() and Adding it to our Canvas
Let's see a code example of how we can add a polyline object to our canvas. The only required parameter is the points Array whereas the second argument is the optional options object.
<!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> Creating an instance of fabric.Polyline() and adding it to our canvas </h2>
<p>You can see that the polyline object has been added</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 points array
var points = [
{ x: 30, y: 50 },
{ x: 0, y: 0 },
{ x: 60, y: 0 },
];
// Initiating a polyline object
var polyline = new fabric.Polyline(points, {
left: 100,
top: 40,
fill: "white",
strokeWidth: 4,
stroke: "cyan",
});
// Adding it to the canvas
canvas.add(polyline);
</script>
</body>
</html>
Example 2: Adding a button to randomly generate the Polyline Objects
Let's see a code example to see how we can randomly generate the Polyline objects. We will add a button on pressing which randomly generated Polyline will be added to the canvas. We will be using a function to randomly generate a Polyline where we will use the Math.random() method to generate random points.
<!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>Adding a button to randomly generate the Polyline objects</h2>
<p> Click on the `Add Polyline!` Button to add a randomly generated polyline to the canvas </p>
<canvas id="canvas"></canvas>
<button type="button" onclick="addPolyline()">Add Polyline!</button>
<script>
// Initiate a canvas instance
var canvas = new fabric.Canvas("canvas");
canvas.setWidth(document.body.scrollWidth);
canvas.setHeight(250);
// Initiate a Polyline object
var polyLine = new fabric.Polyline([
{ x: 500, y: 200 },
{ x: 550, y: 60 },
{ x: 550, y: 200 },
{ x: 350, y: 100 },
{ x: 350, y: 600 },
], {
stroke: "cyan",
fill: "white",
strokeWidth: 5,
});
// Add it to the canvas instance
canvas.add(polyLine);
// Function to generate random Polyline and adding it to canvas
function addPolyline() {
var randomPolyLine = new fabric.Polyline([
{x: Math.random() * 500, y: Math.random() * 200},
{x: Math.random() * 500, y: Math.random() * 600},
{x: Math.random() * 300, y: Math.random() * 100}],
{
stroke: "cyan",
fill: "rgb(256,256,256,0)",
strokeWidth: 5,
});
canvas.add(randomPolyLine)
}
</script>
</body>
</html>
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