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How to calculate the height of a character at a given position in text using FabricJS?

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2023-08-25 08:29:02561browse

如何使用 FabricJS 计算文本中给定位置的字符高度？

In this tutorial, we will learn how to calculate the line height at the desired line index in the text using FabricJS. We can display text on the canvas by adding an instance of Fabric.Text. Not only does it allow us to move, scale and change the dimensions of text, but it also provides additional features such as text alignment, text decoration, line height, which are available through the properties textAlign, underline and lineHeight respectively. We can also calculate the row height at the desired row index using the getHeightOfLine method.

grammar

getHeightOfLine(lineIndex: Number)

parameter

  • lineIndex - This parameter accepts Number as a value. The given value determines the index of the line whose height we want to calculate.

Example 1

Use getHeightOfLine method

Let's look at a code example to see the output logged when using the getHeightOfLine method. In this case, the height of the row at row 1 index will be displayed in the console. 

<!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 getHeightOfLine method</h2>
   <p>You can open console from dev tools and see that the height of line is being displayed in the console </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 text object
      var text = new fabric.Text("Add sampletext here", {
         width: 300,
         fill: "green",
         fontWeight: "bold",
      });

      // Add it to the canvas
      canvas.add(text);

      // Using getHeightOfLine method
      console.log("The height of line is", text.getHeightOfLine(1));
   </script>
</body>
</html>

Example 2

Use getHeightOfLine method and pass different font sizes

Let's look at a code example to see the output logged when using the getHeightOfLine method with a different font size of 30. In this case, the row height at row 0 index will be displayed with the given font size. 

<!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 getHeightOfLine method and passing a different font size</h2>
   <p>You can open console from dev tools and see that the height of line is being displayed in the console </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 text object
      var text = new fabric.Text("Add sampletext here", {
         width: 300,
         fill: "green",
         fontWeight: "bold",
         fontSize: 30
      });

      // Add it to the canvas
      canvas.add(text);

      // Using getHeightOfLine method
      console.log("The height of line is", text.getHeightOfLine(0));
   </script>
</body>
</html>

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