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How to lock the horizontal movement of Line using FabricJS?
In this tutorial, we are going to learn how to lock the horizontal movement of a Line 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. We can also specify whether we want the line object to move only in the Y-axis. This can be done by using the lockMovementX property.
Syntax
new fabric.Line(points: Array, { lockMovementX: Boolean }: Object)
Parameters
points ? This parameter accepts an Array of points which determines the (x1, y1) and (x2, y2) values, those being the x- and y-axis coordinates of the start and end of the line respectively.
options (optional) ? This parameter is an Object which provides additional customizations to our line object. Using this parameter origin, stroke width and a lot of other properties can be changed related to the object of which
lockMovementXis a property.
Options Keys
lockMovementX ? This property accepts a Boolean value. If we assign it a 'true' value, then the object will no longer be able to move in the horizontal direction.
Default behaviour of a Line object in the canvas
Let's see a code example to understand how we can move our line object in the X-axis or the Y-axis freely when lockMovementX property is not assigned a 'true' value.
<!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>Default behaviour of a Line object in the canvas</h2>
<p>
Drag the line object across the x-axis and y-axis to see that movement is allowed in both directions
</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);
</script>
</body>
</html>
Passing lockMovementX as key with 'true' value
In this example, we will see how we can lock the horizontal movement of a line object. By assigning the lockMovementX property a 'true' value, we essentially cease movement in the horizontal direction.
<!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>Passing lockMovementX as key with 'true' value</h2>
<p>
Drag the line object across the x-axis and y-axis to see that movement is no longer allowed in the horizontal direction
</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,
lockMovementX: true,
});
// Add it to the canvas
canvas.add(line);
</script>
</body>
</html>
Key Differences
| Property | Value | Horizontal Movement | Vertical Movement |
|---|---|---|---|
| Default (no lockMovementX) | undefined/false | Allowed | Allowed |
| lockMovementX | true | Locked | Allowed |
Conclusion
The lockMovementX property provides precise control over line object movement in FabricJS. Setting it to true restricts horizontal movement while preserving vertical movement capabilities.
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