如何通过php函数优化图片懒加载效果？

function get_image_urls($html) {
    $pattern = '/<img[^>]+src=["']([^"']+)["'][^>]*>/i';
    preg_match_all($pattern, $html, $matches);
    return $matches[1];
}

$html = file_get_contents('Http://example.com');
$image_urls = get_image_urls($html);

function generate_placeholder($image_url) {
    return '<img src="placeholder.jpg" class="lazy" data-src="' . $image_url . '">';
}

$placeholders = array_map('generate_placeholder', $image_urls);

function load_image($image_url) {
    echo "<script>
        window.addEventListener('scroll', function() {
            var images = document.querySelectorAll('.lazy');
            Array.prototype.forEach.call(images, function(image) {
                var rect = image.getBoundinGClientRect();
                if(rect.top >= 0 && rect.bottom <= (window.innerHeight || document.documentElement.clientHeight)) {
                    image.src = image.dataset.src;
                    image.classList.remove('lazy');
                }
            });
        });
    </script>";
}

array_map('load_image', $image_urls);

.lazy {
    opacity: 0;
    transition: opacity 0.3s;
}

.lazy.show {
    opacity: 1;
}