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When working with images in PHP, various functions provided by the GD library are often used to draw text. imagefontwidth() is one of these, designed to retrieve the width of built-in fonts. However, many developers notice that when trying to use TrueType fonts, the imagefontwidth() function doesn't work as expected. This article will provide an in-depth analysis of the reasons behind this phenomenon.
imagefontwidth() is a function in PHP's GD library, used to return the width of a character in a specified built-in font. Its function prototype is as follows:
imagefontwidth(int $font): int
The $font parameter is an integer representing the number of the built-in font (from 1 to 5). This function only supports the built-in fonts pre-defined in the GD library.
PHP's GD library supports two primary ways of rendering fonts:
Built-in fonts: These are bitmap fonts bundled with the GD library. The font numbers are fixed (from 1 to 5), they are lightweight and fast, but their styles are limited.
TrueType fonts (TTF): Supported by functions like imagettftext(), they allow the use of external .ttf font files, supporting more styles and offering higher quality text rendering.
The imagefontwidth() function was originally designed to query the fixed width of built-in fonts. Its implementation logic is based on pre-defined font data, rather than dynamically parsing font files. The specific reasons are as follows:
Built-in fonts are fixed bitmap fonts
The character width of built-in fonts is pre-defined and fixed, so imagefontwidth() can directly return the corresponding width value.
TrueType fonts need to be dynamically parsed
TrueType font files contain complex vector data, and the character width depends on the metrics in the font file. The widths of different characters may vary (proportional fonts). imagefontwidth() does not have the capability to parse TTF files.
Different functional purposes
imagefontwidth() was designed as an auxiliary function for built-in fonts, while tasks like handling the width of TTF fonts are typically performed by functions like imagettfbbox(), which can return the bounding box of the text and calculate the actual width and height of the string.
For TrueType fonts, it's recommended to use the imagettfbbox() function:
<?php
$fontFile = 'm66.net/fonts/arial.ttf'; // Make sure the font file path is correct
$fontSize = 12;
$text = "Hello, world!";
<p>// Get the text bounding box<br>
$bbox = imagettfbbox($fontSize, 0, $fontFile, $text);</p>
<p>// Calculate the width<br>
$width = abs($bbox[4] - $bbox[0]);</p>
<p>echo "Text width is: " . $width . " pixels";<br>
?><br>
imagettfbbox() returns an array of 8 elements, representing the coordinates of the four corners of the text. By calculating the difference between the horizontal coordinates, you can obtain the text width.
imagefontwidth() can only be used for GD's built-in fonts and cannot handle TrueType fonts.
To calculate the width of TrueType fonts, use the imagettfbbox() function.
Understanding the differences between these two functions helps in correctly using the GD library for high-quality text rendering.
