Poor performance with custom image sizes

I wanted to make this plugin compatible with my custom image sizes. After reading https://github.com/kylereicks/picturefill.js.wp#respond-to-custom-image-sizes my first thought was “Omg why is this so complicated”. Anyway I have edited a bit the code from that article and ended up with following code. It can be improoved but it suits my needs.

function getImages()
{
    $images = array(
        'img-320' => 320,
        'img-768' => 768,
        'img-1024' => 1024,
        'img-1450' => 1450,
        'img-1900' => 1900
    );
    return $images;
}

responsiveImages();

function responsiveImages()
{
    foreach (getImages() as $key => $val) {
        add_image_size($key, $val, false);
        add_image_size($key . '@2x', $val * 2, false);
    }
    add_filter('picturefill_wp_image_sizes', 'theme_remove_thumbnail_from_responsive_image_list', 11, 2);

    function theme_remove_thumbnail_from_responsive_image_list($image_sizes, $image_attributes)
    {
        return array_diff($image_sizes, array('thumbnail', 'thumbnail@2x', 'medium', 'medium@2x', 'large', 'large@2x', 'full'));
    }

    add_filter('picturefill_wp_image_attachment_data', 'theme_picturefill_new_size_attachment_data', 10, 2);

    function theme_picturefill_new_size_attachment_data($attachment_data, $attachment_id)
    {
        $data = array();
        foreach (getImages() as $key => $val) {
            $data[$key] = wp_get_attachment_image_src($attachment_id, $key);
            $data[$key . '@2x'] = wp_get_attachment_image_src($attachment_id, $key . '@2x');
        }
        return array_merge($attachment_data, $data);
    }

    // Add the new image size(s) to the responsive queue
    add_filter('picturefill_wp_image_sizes', 'theme_add_new_small_size_to_responsive_image_list', 11, 2);

    function theme_add_new_small_size_to_responsive_image_list($image_sizes, $image_attributes)
    {
        $data = array(); //'thumbnail', 'medium', 'large', 'full');
        foreach (getImages() as $key => $val) {
            array_push($data, $key);
            array_push($data, $key . '@2x');
        }
        if (!in_array($image_attributes['min_size'], $data)) {
            return $data;
        } else {
            return $image_sizes;
        }
    }

    // Set the breakpoint for the new image as a new size
    add_filter('picturefill_wp_media_query_breakpoint', 'theme_picturefill_new_small_size_breakpoint', 10, 3);

    function theme_picturefill_new_small_size_breakpoint($breakpoint, $image_size, $width)
    {
        foreach (getImages() as $key => $val) {
            if (in_array($image_size, array($key, $key . '@2x')))
                return $val;
        }
        return $breakpoint;
    }

}

I think that everything is properly done here but still there is one critical bug. When I open any website with picturefill code the above code is executed and the filter “picturefill_wp_image_attachment_data” is applied in file picturefillwp\inc\class-model-picturefill-wp.php on line 100. After that there is this loop

foreach($image_attachment_data as $attachment_size => $attachment_data){
          if($this->image_needs_to_be_created($image_attachment_data, $attachment_size, $attachment_data)){
            $new_meta_data = wp_generate_attachment_metadata($attachment_id, get_attached_file($attachment_id));
            wp_update_attachment_metadata($attachment_id, $new_meta_data);
            $image_attachment_data[$attachment_size] = wp_get_attachment_image_src($attachment_id, $attachment_size);
          }
        }

Which increases load time about 10 times longer. When there is more that one image (in my case about 15) page loads in 20 minutes… When I comment out this loop. Everything works fine and page loads instantly. Whats the point of this loop? Can this be fixed?

http://wordpress.org/plugins/picturefillwp/