Gallery page using ACF PRO with a dynamically generated zip file download of all gallery images.

page-gallery.php

<?php // Check the gallery field (created with ACF PRO) for images
$images = get_field('images');
if( $images ) :
// If it does have images:

	// Create variable for download file
	// This uses a /downloads/ directory and the page title as the file name
        $pasta_download = 'wp-content/galerias-download/';

        if (!file_exists($pasta_download)) {
            mkdir($pasta_download, 0777, true);
        }
        
        $destination = $pasta_download . '' . sanitize_title( get_the_title() ) . '.zip';
        
	// Check if the file already exists (see tutorial for a cautionary note)
	if ( file_exists( $destination ) ) {

		// If it exists, print the download link
		echo '<a href="' . esc_url( home_url( '/' ) ) . $destination . '" class="download-link" download>DOWNLOAD ALL</a>';

	} else {
		
		// If the file doesn't already exist, create the file
		$files = array();
		foreach( $images as $singlefile ) {
			// create an array of the image files in the gallery
			$files[] = get_attached_file( $singlefile['ID'] );
		}
		
		if( count( $files ) ) {
			// Check if there are files in the array (files exist)
			// If there are files, create a zip file in the location specified
			$zip = new ZipArchive();
			$zip->open( $destination, ZipArchive::CREATE );
			
			foreach( $files as $file ) {
				// for every file in the array
				if ( file_exists($file) ) {
					// if the file actually exists, add it to the zip file
					$new_filename = substr($file,strrpos($file,'/') + 1);
					$zip->addFile( $file, $new_filename );
				}
			}
			
			// Once you've got all the files, close out the zip
			$zip->close();
			
			// Then link to the file you just created
			echo '<a href="' . esc_url( home_url( '/' ) ) . $destination . '" class="download-link" download>DOWNLOAD ALL</a>';

		} else {
			// No images are found, display an error message
			echo 'no files found';
		}
	} ?>
 
	<!-- Next, display the on-page gallery -->
	<div class="gallery-grid">
        <?php foreach( $images as $image ) : 
        	// For every image in the gallery, display the thumbnail linked to a larger image for a lightbox ?>
        	<a href="<?php echo $image['url']; ?>" title="<?php echo $image['title']; ?>" rel="gallery">
           		<img src="<?php echo $image['sizes']['thumbnail']; ?>" alt="<?php echo $image['alt']; ?>" />
           	</a>
        <?php endforeach; ?>
    </div><!-- / .gallery-grid -->
    
<?php else : 
// If the gallery field is empty: ?>
	
	<p>No images found.</p>
	
<?php endif; ?>