PHP add watermark with centered diagonal text

watermark.php

<?php
// recursive search by pattern
function rsearch($folder, $pattern) {
    $dir = new RecursiveDirectoryIterator($folder);
    $ite = new RecursiveIteratorIterator($dir);
    $files = new RegexIterator($ite, $pattern, RegexIterator::GET_MATCH);
    $fileList = array();
    foreach($files as $file) {
        $fileList = array_merge($fileList, $file);
    }
    return $fileList;
}

function addWatermark($image)
{
    $im = imagecreatefromjpeg($image);
    $font = dirname(__FILE__) . '/comic.ttf';
    $text = 'some text';
    $angle = 45; // rotate 45 degrees
    $transparency = 0.2;
    $text_opacity = 100 - $transparency * 100;

    $white = imagecolorallocatealpha($im, 255, 255, 255, $text_opacity);
    $shadow = imagecolorallocatealpha($im, 0, 0, 0, 95);

    $width = imagesx($im);
    $font_size = $width / 15; // font size relative to image width

    $height = imagesy($im);
    $centerX = $width / 2;
    $centerY = $height / 2;

    // Get size of text
    list($left, $bottom, $right, , , $top) = imageftbbox($font_size, $angle, $font, $text);

    // Determine offset of text
    $left_offset = ($right - $left) / 2;
    $top_offset = ($bottom - $top) / 2;

    // Generate coordinates
    $x = $centerX - $left_offset;
    $y = $centerY + $top_offset;

    imagettftext($im, $font_size, $angle, $x + 3, $y + 3, $shadow, $font, $text); // add shadow
    imagettftext($im, $font_size, $angle, $x, $y, $white, $font, $text); // add text
  
    imagejpeg($im, $image); // override image with watermark image
    imagedestroy($im); // free memory
}

$dirname = './directory/img/';
$images = rsearch($dirname, "/.*-(?:large|medium)_default\.jpg/");

foreach ($images as $filename) {
    addWatermark($filename);
}