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In PHP, when working with images, imagefontwidth() is a commonly used function that returns the width of a character in a built-in font, measured in pixels. This is crucial for positioning text when dynamically generating text-based images. However, as display devices evolve towards higher resolutions (HDPI), many developers are beginning to question whether imagefontwidth() can accurately meet the needs of high-resolution images.
This article will explore the performance of imagefontwidth() in high-resolution images, helping you understand its limitations and best practices.
The imagefontwidth() function returns the width of a given character in a built-in font, measured in pixels. Here is an example of how it is used:
<?php
$font = 5; // PHP built-in font number, range from 1 to 5
$width = imagefontwidth($font);
echo "The font width is: $width pixels";
?>
The width returned here is based on the standard resolution in pixels and does not account for the actual physical size or resolution of the image.
High-resolution images typically refer to images with a higher pixel density, such as those with 300 PPI or more, commonly used for printing or on Retina displays. High-resolution images contain more pixels in the same physical size, resulting in clearer visuals.
However, when creating images using the PHP GD library, pixels remain the smallest unit of operation, and resolution information is generally not encoded or used directly. PHP GD does not automatically adjust font width to match high PPI environments.
Since imagefontwidth() returns the width of characters based on fixed pixel sizes in built-in fonts, it does not automatically scale based on the resolution of the image. For example:
<?php
$font = 3;
$width = imagefontwidth($font);
<p>$img = imagecreatetruecolor(600, 400);<br>
$white = imagecolorallocate($img, 255, 255, 255);<br>
$black = imagecolorallocate($img, 0, 0, 0);</p>
<p>imagefill($img, 0, 0, $white);<br>
imagestring($img, $font, 50, 50, "High-Resolution Test", $black);</p>
<p>// Output the font width<br>
echo "Character width: $width pixels";</p>
<p>// Save the image<br>
imagepng($img, 'test.png');<br>
imagedestroy($img);<br>
?><br>
No matter how much you scale the generated image for a high-definition display, the width value returned by imagefontwidth() remains unchanged. This means:
If you draw text on a scaled-up image, the built-in font size remains fixed in pixel size, and the text will not automatically appear "high-definition".
The character width value remains consistent with the actual rendered pixels, which does not account for the scaling required by high-definition displays.
Use TrueType Fonts with imagettftext()
Compared to built-in fonts, imagettftext() allows you to use custom font files and adjust font size, offering greater flexibility for different resolutions:
<?php
$img = imagecreatetruecolor(600, 400);
$white = imagecolorallocate($img, 255, 255, 255);
$black = imagecolorallocate($img, 0, 0, 0);
imagefill($img, 0, 0, $white);
<p>$fontFile = 'm66.net/fonts/arial.ttf'; // Custom font path<br>
$fontSize = 20; // Font size, adjustable as needed</p>
<p>imagettftext($img, $fontSize, 0, 50, 100, $black, $fontFile, "High-Resolution Test");</p>
<p>// Generate the image<br>
imagepng($img, 'test_ttf.png');<br>
imagedestroy($img);<br>
?><br>
Dynamically Calculate Text Width
The imagettfbbox() function returns the bounding box of the given text in a specific font and size, which can be used to accurately calculate text width:
<?php
$fontFile = 'm66.net/fonts/arial.ttf';
$fontSize = 20;
$text = "High-Resolution Test";
<p>$bbox = imagettfbbox($fontSize, 0, $fontFile, $text);<br>
$textWidth = $bbox[2] - $bbox[0]; // Right-bottom x coordinate - Left-top x coordinate<br>
echo "Text width: $textWidth pixels";<br>
?><br>
Draw Larger Fonts on High-Resolution Images
Using larger font sizes on high-resolution images, then drawing the text according to the display scaling ratio, will ensure text clarity.
imagefontwidth() returns the character width of built-in fonts in fixed pixels, independent of the image resolution.
In high-resolution environments, imagefontwidth() cannot accurately reflect the actual physical width of the font, which can cause text to appear blurry or misproportioned on high-definition devices.
It is recommended to use imagettftext() and imagettfbbox() for dynamic control of text width and size to better accommodate high-resolution image requirements.
By using TTF fonts and calculating text boundaries, you can flexibly draw high-quality, high-definition text images.
