Adjust text tracking with PHP/FreeType

imagettftext_tracking.php

<?php

/**
 * This is based on the work of ryan at retronetworks dot com
 * Who posted the original function on the PHP manual.
 * I had occasion to find the pixel width of the created string so now
 * a) the function returns the length 
 * and b) there's a stripped-down imagettfbbox which does the same thing
 * 
 * Ryan's original code: http://www.php.net/manual/en/function.imagettfbbox.php#51373
 */

/**
 * Get the length of a FreeType text string with specified tracking. Does not write into an image.
 * 
 * @param the same as imagettfbbox() with an extra $tracking variable in pixels
 * 
 * @return the width of the created string
 */
function imagettfbbox_width_with_tracking( $size, $angle, $fontfile, $text, $tracking ) {

	$numchar = strlen($text);

	$w = 0;

	for($i = 0; $i < $numchar; $i++) {

		$char[$i] = substr($text, $i, 1);

		$char_dimensions = imagettfbbox( $size, $angle, $fontfile, $char[$i] );

		$w += $char_dimensions[2];
	}

	return $w + ( $numchar * $tracking );
}

/**
 * Use FreeType to write a text string into an image
 * 
 * @param the same as imagettftext() with an extra $tracking variable in pixels
 * 
 * @return the width of the created string
 */
function imagettftext_with_tracking( $im, $size, $angle, $x, $y, $color, $font, $text, $tracking ) {

	$numchar = strlen($text);

	$w = 0;
	$characters_width = 0;

	for($i = 0; $i < $numchar; $i++) {

		$char[$i] = substr($text, $i, 1);

		imagettftext($im, $size, $angle, ($x + $w + ($i * $tracking) ), $y, $color, $font, $char[$i]);
	   
		$char_dimensions = imagettfbbox($size, $angle, $font, $char[$i]);

		$characters_width += $char_dimensions[2];
		$w = $w + $char_dimensions[2];
	}

	return $characters_width + ( $numchar * $tracking );
}