Thumbnail creator in PHP

.htaccess

<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteRule ^(.*)$ ../thumb.php [QSA,L]
</IfModule>

example.html

<img src="400x300.myimage.jpg" />
<img src="200x200-crop.myimage.jpg" />

thumb.php

<?php
function createthumb($name, $filename, $new_w, $new_h, $crop=false)
{
    $ext = strtolower(pathinfo($name, PATHINFO_EXTENSION));

    if ($ext =='jpg') $ext = 'jpeg';
    $fn_create = "imagecreatefrom$ext";
    $fn_out = "image$ext";

    if (!function_exists($fn_create)) throw new Exception("Unsupported extension '$ext' for '$name'");

    $src_img = $fn_create($name);

    $old_w = imageSX($src_img);
    $old_h = imageSY($src_img);
    $old_x = 0;
    $old_y = 0;

    if ($old_w < $new_w && $old_h < $new_h) {
        copy($name, $filename);
        return;
    }
    
    if (($old_w / $new_w) > ($old_h / $new_h) xor $crop) {
        $thumb_w=$new_w;
        $thumb_h=$old_h*($new_w/$old_w);
        if ($crop) $old_y = floor(0.5 * ($thumb_h - $new_h) * ($new_w/$old_w));
    } else {
        $thumb_w=$old_w*($new_h/$old_h);
        $thumb_h=$new_h;
        if ($crop) $old_x = floor(0.5 * ($thumb_w - $new_w) * ($new_h/$old_h));
    }

    $dst_img = imagecreatetruecolor($crop ? $new_w : $thumb_w, $crop ? $new_h : $thumb_h);
    imagesavealpha($dst_img, true);
    $trans_colour = imagecolorallocatealpha($dst_img, 0, 0, 0, 127);
    imagefill($dst_img, 0, 0, $trans_colour);
    
    imagecopyresampled($dst_img, $src_img, 0, 0, $old_x, $old_y, $thumb_w, $thumb_h, $old_w, $old_h);

    $fn_out($dst_img, $filename); 

    imagedestroy($dst_img); 
    imagedestroy($src_img); 
}

$newfile = rtrim($_SERVER['DOCUMENT_ROOT'], '/') . '/' . ltrim(isset($_GET['name']) ? $_GET['name'] : preg_replace('/\?.*$/', '', $_SERVER['REQUEST_URI']), '/');
$dir = dirname($newfile);

if (!preg_match('/^(\d+)x(\d+)(?:-(crop))?\.(.*\.(.*?))$/', basename($newfile), $match)) {
    header('HTTP/1.0 404 Not Found');
    echo "Illegal filename '$newfile'";
    exit;
} 

list(, $width, $height, $crop, $name, $ext) = $match;

createthumb("$dir/$name", $newfile, $width, $height, (bool)$crop);

if (!file_exists($newfile)) {
    header('HTTP/1.0 500 Internal Server Error');
    echo "Could not write to '$newfile'";
    exit;
}

$ext = strtolower($ext);
if ($ext =='jpg') $ext = 'jpeg';

header("Content-Type: image/$ext");
readfile($newfile);