timeline/libs/__Thumbnail.php

<?php

// Based on: https://github.com/Francesco-Chen/Thumbnail-Gallery-PHP

function createThumbnail($src, $dest, $thumbHeight) {
    list($width, $height, $type) = getimagesize($src);
    $aspectRatio = $width / $height;
    $thumbWidth = $thumbHeight * $aspectRatio;

    switch ($type) {
        case IMAGETYPE_JPEG:
            $image = imagecreatefromjpeg($src);
            break;
        case IMAGETYPE_PNG:
            $image = imagecreatefrompng($src);
            break;
        case IMAGETYPE_WEBP: // Support webp format
            $image = imagecreatefromwebp($src);
            break;
        default:
            return false; // Unsupported image type
    }

    $thumb = imagecreatetruecolor($thumbWidth, $thumbHeight);

    imagecopyresampled($thumb, $image, 0, 0, 0, 0, $thumbWidth, $thumbHeight, $width, $height);

    switch ($type) {
        case IMAGETYPE_JPEG:
            imagejpeg($thumb, $dest);
            break;
        case IMAGETYPE_PNG:
            imagepng($thumb, $dest);
            break;
        case IMAGETYPE_WEBP: // Support webp format
            imagewebp($thumb, $dest);
            break;
    }

    imagedestroy($thumb);
    imagedestroy($image);
    return true;
}

$galleryDir = "gallery/";
$thumbDir = "thumb/";
$allowedExtensions = array("jpg", "jpeg", "png", "gif", "webp"); // Remove "mp4" from allowed extensions

// Check and create the "thumb" directory if it doesn't exist
if (!file_exists($thumbDir)) {
    mkdir($thumbDir);
}

$galleryFiles = scandir($galleryDir);

foreach ($galleryFiles as $file) {
    $extension = pathinfo($file, PATHINFO_EXTENSION);
    if (in_array(strtolower($extension), $allowedExtensions)) {
        $imageURL = $galleryDir . $file;
        $thumbURL = $thumbDir . $file;

        if (!file_exists($thumbURL)) {
            createThumbnail($imageURL, $thumbURL, 200); // The thumbnail will have a height of 200 pixels.
        }

        echo '
            <a
                data-fancybox="gallery"
                data-src="' . $imageURL . '"
                data-caption="' . $file . '"
            >
                <img src="' . $thumbURL . '" height="200" />
            </a>
        ';
    }
}

?>