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FabricJS – Removing the object transformations of a Polygon converted to an HTMLCanvasElement?
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.
In order to convert a polygon object into HTMLCanvasElement we use the toCanvasElement method. It returns the DOM element of type HTMLCanvasElement, an interface which inherits its properties and methods from the HTMLElement interface. We use the withoutTransform property to remove object transformations of the Polygon converted to HTMLCanvasElement.
Syntax
toCanvasElement({ withoutTransform: Boolean }: Object):
HTMLCanvasElement
Parameters
options (optional) − This parameter accepts an Object which provides additional customizations to our HTMLCanvasElement. Using this parameter height, left crop offset and a lot of other properties can be changed related to the HTMLCanvasElement of which withoutTransform is a property.
Options Keys
withoutTransform − This property accepts a Boolean value which determines whether the current object transform is to be removed or not. This property is optional.
Example 1: Using the withoutTransform Property and Passing it a ‘false’ Value
Let’s see a code example to see the logged output when the toCanvasElement method is used along with withoutTransform property. On passing it a ‘false’ value, the withoutTransform property retains its object transformations. Therefore, in this case, scaleX, scaleY and flipX object transformations will be present in its output image. We have used the toDataURL method in sync with toCanvasElement method to show how the output image actually looks.
<!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 withoutTransform property and passing it a ‘false’ value</h2>
<p>
You can open console from dev tools, copy the url string and paste it in a new tab to see that the polygon object's image contains object transformation
</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,
flipX: true,
}
);
// Adding it to the canvas
canvas.add(polygon);
// Using toCanvasElement method
var withoutTransform = polygon.toCanvasElement({
withoutTransform: false,
});
// Using toDataURL method
console.log(withoutTransform.toDataURL());
</script>
</body>
</html>
Example 2: Using the withoutTransform Property and Passing it a ‘true’ Value
Let’s see a code example to see the logged output when the toCanvasElement method is used along with withoutTransform property. On passing it a ‘true’ value, the withoutTransform property will not retain its object transformations. Therefore, in this case, scaleX, scaleY and flipX object transformations will be removed in its output image.
<!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 withoutTransform property and passing it a ‘true’ value</h2>
<p>
You can open console from dev tools, copy the url string and paste it in a new tab to see that the polygon object's image does not contain object transformation
</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,
flipX: true,
}
);
// Adding it to the canvas
canvas.add(polygon);
// Using toCanvasElement method
var withoutTransform = polygon.toCanvasElement({
withoutTransform: true,
});
// Using toDataURL method
console.log(withoutTransform.toDataURL());
</script>
</body>
</html>
Conclusion
In this tutorial, we used two simple examples to demonstrate how to remove object transformations of a Polygon converted to an HTMLCanvasElement using FabricJS.
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