Web Front-endJS TutorialFabricJS - Find the drawing context of a Polygon object converted to an HTMLCanvasElement?FabricJS - Find the drawing context of a Polygon object converted to an HTMLCanvasElement?
We can create Polygon objects by creating instances 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.
To convert a polygon object to a HTMLCanvasElement, we use the toCanvasElement method. It returns a DOM element of type HTMLCanvasElement, which inherits its properties and methods from the HTMLElement interface. We use the getContext method to find the drawing context on the canvas. If the context ID is not supported, a null value is returned.
Grammar
HTMLCanvasElement.getContext():
Example 1: Using toCanvasElement method
Let's look at a code example to see the output logged when using the toCanvasElement method. When using the toCanvasElement method, a DOM element of type HTMLCanvasElement is returned. You can open the console from the dev tools to see that the DOM element of type HTMLCanvasElement is being returned.
<!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="Using-the-toCanvasElement-method">Using the toCanvasElement method</h2>
<p>You can open 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 object
var polygon = new fabric.Polygon(
[
{ x: 600, y: 310 },
{ x: 650, y: 450 },
{ x: 600, y: 480 },
{ x: 550, y: 480 },
{ x: 450, y: 460 },
{ x: 300, y: 210 },
],
{
fill: "#778899",
stroke: "blue",
strokeWidth: 5,
top: 50,
left: 100,
scaleX: 0.5,
scaleY: 0.5,
}
);
// Adding it to the canvas
canvas.add(polygon);
// Using toCanvasElement method
console.log(
"The output on using toCanvasElement method is:",
polygon.toCanvasElement()
);
</script>
</body>
</html>
Example 2: Using the getContext method
Let's look at a code example of the output logged when using the getContext method and the toCanvasElement method to find the drawing context of a Polygon object converted to an HTMLCanvasElement. The drawing context allows us to draw on the canvas. Since we passed the value "2d" to the getContext method, a CanvasRenderingContext2D object is returned.
<!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="Using-getContext-method">Using getContext method</h2>
<p>
You can open console from dev tools to see that the CanvasRenderingContext2D object is being returned
</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 polygon = new fabric.Polygon(
[
{ x: 600, y: 310 },
{ x: 650, y: 450 },
{ x: 600, y: 480 },
{ x: 550, y: 480 },
{ x: 450, y: 460 },
{ x: 300, y: 210 },
],
{
fill: "#778899",
stroke: "blue",
strokeWidth: 5,
top: 50,
left: 100,
scaleX: 0.5,
scaleY: 0.5,
}
);
// Adding it to the canvas
canvas.add(polygon);
// Using toCanvasElement method
var polygonCanvas = polygon.toCanvasElement({
width: 200,
});
// Using getContext method
console.log(
"The drawing context of a Polygon object converted to HTMLCanvasElement is as follows:",
polygonCanvas.getContext("2d")
);
</script>
</body>
</html>
in conclusion
In this tutorial, we use two simple examples to demonstrate how to find the drawing context of a Polygon object converted to an HTMLCanvasElement using FabricJS.
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