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When performing image processing with PHP, dynamically generating text is one of the common requirements, such as generating CAPTCHA, user avatars, chart labels, and more. However, to ensure that the text aligns correctly in the image, you must accurately calculate its pixel width and height. imageftbbox is an essential tool for this task. This article will dive into how to use this function and provide practical tips to help you control the text layout in images with precision.
imageftbbox is a function in PHP's GD library used to calculate the bounding box of text rendered using TrueType fonts (TTF). The return value is an array representing the coordinates of the four corners of the bounding box containing the text.
array imageftbbox ( float $size , float $angle , string $fontfile , string $text [, array $options ] )
$size: Font size.
$angle: The angle of the text (clockwise).
$fontfile: Path to the font file.
$text: The text string to be measured.
$options: Optional parameters such as letter spacing.
imageftbbox returns an array with 8 elements, representing the (x, y) coordinates of the four corners of the bounding box, in the following order:
[
0 => lower left x,
1 => lower left y,
2 => lower right x,
3 => lower right y,
4 => upper right x,
5 => upper right y,
6 => upper left x,
7 => upper left y
]
To calculate the "actual" width and height of the text, use the following formulas:
$width = abs($bbox[2] - $bbox[0]);
$height = abs($bbox[5] - $bbox[1]);
Below is a complete PHP example demonstrating how to calculate the width and height of text and center it on an image.
<?php
<p>// Font path (TTF format)<br>
$font = <strong>DIR</strong> . '/fonts/arial.ttf';</p>
<p>// Text content<br>
$text = "Hello Gitbox!";</p>
<p>// Font size and angle<br>
$size = 20;<br>
$angle = 0;</p>
<p>// Calculate the bounding box<br>
$bbox = imageftbbox($size, $angle, $font, $text);</p>
<p>// Calculate width and height<br>
$width = abs($bbox[2] - $bbox[0]);<br>
$height = abs($bbox[5] - $bbox[1]);</p>
<p>// Create the image<br>
$imageWidth = $width + 20;<br>
$imageHeight = $height + 20;<br>
$image = imagecreatetruecolor($imageWidth, $imageHeight);</p>
<p>// Set colors<br>
$white = imagecolorallocate($image, 255, 255, 255);<br>
$black = imagecolorallocate($image, 0, 0, 0);<br>
imagefill($image, 0, 0, $white);</p>
<p>// Calculate starting coordinates to center the text<br>
$x = ($imageWidth - $width) / 2 - $bbox[0];<br>
$y = ($imageHeight - $height) / 2 - $bbox[5];</p>
<p>// Draw the text<br>
imagefttext($image, $size, $angle, $x, $y, $black, $font, $text);</p>
<p>// Output the image<br>
header("Content-Type: image/png");<br>
imagepng($image);<br>
imagedestroy($image);<br>
?><br>
You can save the above code as a .php file and access it through a browser, such as deploying it at https://gitbox.net/demo/text-center.php, where you can see the text accurately centered in the image.
Always use abs(): The coordinates returned by bbox might be negative, so always use abs() to calculate the width and height.
Leave enough padding: To prevent the font from being cropped, it's recommended to add extra padding to the image size (as shown with +20 in the example above).
Check font compatibility: Ensure the font path is correct on the server, especially when deploying across different operating systems or containerized environments.
Handle multi-line text: For multi-line text, calculate the bounding box for each line separately and then combine them for layout.
imageftbbox is a powerful but often overlooked tool, and mastering it can greatly enhance your flexibility and accuracy in image layout. With the information provided, you should now be able to accurately calculate text width and height and apply it flexibly to your projects. If you want to add adaptive watermarks, labels, or data annotations to your images, practice more to make the text and images truly merge.
By deeply understanding imageftbbox, your image processing capabilities will reach a new level.
