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FabricJS - How to center a Line object in the current viewport of the canvas?

王林
王林forward
2023-08-24 22:41:05738browse

FabricJS – 如何将 Line 对象置于画布当前视口的中心？

In this tutorial, we will learn how to center a Line object horizontally and vertically in the current viewport of the canvas using FabricJS. Line element is one of the basic elements provided in FabricJS. It is used to create straight lines. Since line elements are geometrically one-dimensional and contain no interiors, 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. To center the Line object on the current viewport of the canvas, we use the viewportCenter method.

Syntax

 viewportCenter(): fabric.Object

Default appearance of Line objects

Example

Let’s look at a code example to see how it works without using viewportCenter The method is the appearance of the Line object. In this case, the line object will not be centered on the canvas. 

<!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 appearance of the Line object</h2>
   <p>
      You can see that the line object is not centered with respect to the current viewport of canvas
   </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>

Using viewportCenterMethod

Example

Let's look at a code example to see what a line object looks like when using the viewportCenter method. In this case, our line object will be centered relative to the current viewport of the canvas. 

<!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 viewportCenter method</h2>
   <p>
      You can see that the line object is centered with respect to the current viewport of canvas 
   </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 the viewportCenter method
      line.viewportCenter();
   </script>
</body>
</html>

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