How to optimize the lazy loading effect of images through php functions?

How to optimize the lazy loading effect of images through PHP functions?

With the development of the Internet, the number of images in web pages is increasing, which puts pressure on page loading speed. In order to improve user experience and reduce loading time, we can use image lazy loading technology. Lazy loading of images can delay the loading of images. Images are only loaded when the user scrolls to the visible area, which can reduce the loading time of the page and improve the user experience.

When writing PHP web pages, we can optimize the lazy loading effect of images by writing some functions. The following describes in detail how to implement lazy loading of images through PHP functions.

The first step is to get all the image links
First, we need to get the links to all the images in the current page. This can be achieved by using the preg_match_all function and regular expressions, as shown below:

function get_image_urls($html) {
    $pattern = '/<img  class="lazy lazy"  src="/static/imghw/default1.png"  data-src="placeholder.jpg" [^ alt="How to optimize the lazy loading effect of images through php functions?" >]+src=["']([^"']+)["'][^>]*>/i';
    preg_match_all($pattern, $html, $matches);
    return $matches[1];
}

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

The second step is to generate the image placeholder
Before the page is loaded, we need to Generate a placeholder for each image to be loaded lazily, which can avoid page layout reflow. We can use the data-src attribute of the <img class="lazy lazy" src="/static/imghw/default1.png" data-src="placeholder.jpg" alt="How to optimize the lazy loading effect of images through php functions?" > tag to save the real link of the image and use a placeholder to display the image.

function generate_placeholder($image_url) {
    return '<img  class="lazy lazy"  src="/static/imghw/default1.png"  data-src="placeholder.jpg"  data- . $image_url . '" alt="How to optimize the lazy loading effect of images through php functions?" >';
}

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

In the above code, placeholder.jpg is a placeholder image and can be replaced with other images according to the actual situation. lazy The class can be used to identify lazy loaded images.

The third step, listen to the page scroll event
We need to monitor the user's scrolling behavior. When the user scrolls to the visible area of ​​​​the image, we assign the real link of the image to src Attribute to implement image loading.

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);

In the above code, we use JavaScript to listen to the scroll event of the page and determine whether to load the image based on whether the image is within the visible area.

The fourth step, style optimization
In order to optimize the user experience, we can add some progressive loading effects to the images, such as fade-in and fade-out effects. This can be achieved through CSS.

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

.lazy.show {
    opacity: 1;
}

In CSS, we set a transition effect for the .lazy class. When the image is loaded, add the .show class to display the image.

Summary
Through the above PHP function, we can achieve the lazy loading effect of images. First, get the links of all images on the page, then generate placeholders, listen to page scroll events to determine whether to load images, and add style optimization. This can effectively reduce page loading time and improve user experience.

The code provided above is just an example, you can modify and optimize it according to your needs and actual situation. hope it is of help to you!

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