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FabricJS β Finding the drawing context of a Polygon object 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 getContext method to find a drawing context on the canvas. It returns a null value if context ID is not supported.
Syntax
HTMLCanvasElement.getContext():
Example 1: Using the toCanvasElement Method
Letβs see a code example to see the logged output when the toCanvasElement method is used. On using the toCanvasElement method, the DOM element of type HTMLCanvasElement is returned. You can open the console from 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>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 getContext Method
Letβs see a code example to see the logged output when the getContext method is used along with toCanvasElement method to find the drawing context of Polygon object converted to HTMLCanvasElement. A drawing context is what lets us draw on the canvas. Since we are passing the getContext method a value of β2dβ, 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>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>
Conclusion
In this tutorial, we used two simple examples to demonstrate how you can find the drawing context of a Polygon object converted to an HTMLCanvasElement using FabricJS.
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