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FabricJS – How to get the coordinates of a Line object as if it has a different origin?
In this tutorial, we are going to learn about how to get the coordinates of a Line as if it has a different origin using FabricJS. A Line element is one of the basic elements provided in FabricJS. It is used for creating straight lines. Because line elements are geometrically one-dimensional and do not contain an interior, they are never filled. We can create a line object by creating an instance of fabric.Line, specifying the x and y coordinates of the line and adding it to the canvas. In order to find the coordinates of a Line object as if it has a different origin, we use the getPointByOrigin method.
Syntax
getPointByOrigin(originX: String, originY: String): fabric.Point
Parameters
originX? This parameter accepts a String which specifies the horizontal origin. The possible values are 'left', 'center' or 'right'.originY? This parameter accepts a String which denotes the vertical origin. The possible values are 'top', 'center' or 'bottom'.
Using getPointByOrigin Method
Let's see a code example to see the logged output when the getPointByOrigin method is used. The getPointByOrigin method returns the coordinates of an object for a user specified origin. In this case, we have used the getCenterPoint method as well so that you can see the real center points of the given Line object. Whereas while using the getPointByOrigin method, we have taken the bottom left point as origin and therefore the logged output is x= 100 and y= 120.
<!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 getPointByOrigin method</h2>
<p>
You can open console from dev tools and see that the logged output contains the coordinates
</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 Line object
var line = new fabric.Line([200, 100, 100, 40], {
stroke: "blue",
strokeWidth: 20,
});
// Add it to the canvas
canvas.add(line);
// Using getCenterPoint method
console.log(
"The real center point of the object is: ",
line.getCenterPoint()
);
// Using getPointByOrigin method
console.log(
"The coordinates returned while using getPointByOrigin method are: ",
line.getPointByOrigin("left", "bottom")
);
</script>
</body>
</html>
The real center point of the object is: {x: 150, y: 70}
The coordinates returned while using getPointByOrigin method are: {x: 100, y: 120}
Using getPointByOrigin Method with Different Values
In this example, we have used the getPointByOrigin method to obtain the coordinates of the Line object when the horizontal and vertical center points are 'right' and 'top'. This means the top-right point will be considered as center.
<!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 getPointByOrigin method with different values</h2>
<p>
You can open console from dev tools and see that the logged output contains the coordinates
</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 Line object
var line = new fabric.Line([200, 100, 100, 40], {
stroke: "blue",
strokeWidth: 20,
});
// Add it to the canvas
canvas.add(line);
// Using getPointByOrigin method
console.log(
"The coordinates returned while using getPointByOrigin method are: ",
line.getPointByOrigin("right", "top")
);
</script>
</body>
</html>
The coordinates returned while using getPointByOrigin method are: {x: 200, y: 20}
How It Works
The getPointByOrigin method calculates coordinates based on the specified origin points. When you set originX to 'left' and originY to 'bottom', it returns coordinates as if the object's reference point is at its bottom-left corner. Similarly, 'right' and 'top' origins treat the top-right corner as the reference point.
Conclusion
The getPointByOrigin method is useful for calculating object positions relative to different reference points. This is particularly helpful when you need to align or position objects based on specific corners or edges rather than the default center origin.
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