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AMP for WordPress

Overview

This plugin adds support for the Accelerated Mobile Pages (AMP) Project, which is an open source initiative that aims to provide mobile optimized content that can load instantly everywhere.

With the plugin active, all posts on your site will have dynamically generated AMP-compatible versions, accessible by appending /amp/ to the end your post URLs. For example, if your post URL is http://example.com/2016/01/01/amp-on/, you can access the AMP version at http://example.com/2016/01/01/amp-on/amp/. If you do not have pretty permalinks enabled, you can do the same thing by appending ?amp=1, i.e. http://example.com/?p=123&amp=1

Note #1: that Pages and archives are not currently supported.

Note #2: this plugin only creates AMP content but does not automatically display it to your users when they visit from a mobile device. That is handled by AMP consumers such as Google Search. For more details, see the AMP Project FAQ.

Customization / Templating

The plugin ships with a default template that looks nice and clean and we tried to find a good balance between ease and extensibility when it comes to customization.

You can tweak small pieces of the template or the entire thing depending on your needs.

Where Do I Put My Code?

The code snippets below and any other code-level customizations should happen in one of the following locations.

If you're using an off-the-shelf theme (like from the WordPress.org Theme Directory):

If you're using a custom theme:

  • functions.php (or via a 'require' call to files that load from functions.php).
  • Any of the options above.

Theme Mods

The default template will attempt to draw from various theme mods, such as site icon, if supported by the active theme.

Site Icon

If you add a site icon, we will automatically replace the WordPress logo in the template.

If you'd prefer to do it via code:

add_filter( 'amp_post_template_data', 'xyz_amp_set_site_icon_url' );

function xyz_amp_set_site_icon_url( $data ) {
    // Ideally a 32x32 image
    $data[ 'site_icon_url' ] = get_stylesheet_directory_uri() . '/images/amp-site-icon.png';
    return $data;
}

Logo Only

If you want to hide the site text and just show a logo, use the amp_post_template_css action. The following colors the title bar black, hides the site title, and replaces it with a centered logo:

add_action( 'amp_post_template_css', 'xyz_amp_additional_css_styles' );

function xyz_amp_additional_css_styles( $amp_template ) {
    // only CSS here please...
    ?>
    header.amp-wp-header {
        padding: 12px 0;
        background: #000;
    }
    header.amp-wp-header a {
        background-image: url( 'https://example.com/path/to/logo.png' );
        background-repeat: no-repeat;
        background-size: contain;
        display: block;
        height: 28px;
        width: 94px;
        margin: 0 auto;
        text-indent: -9999px;
    }
    <?php
}

Note: you will need to adjust the colors and sizes based on your brand.

Template Tweaks

You can tweak various parts of the template via code.

Featured Image

The default template does not display the featured image currently. There are many ways to add it, such as the snippet below:

add_action( 'pre_amp_render_post', 'xyz_amp_add_custom_actions' );
function xyz_amp_add_custom_actions() {
    add_filter( 'the_content', 'xyz_amp_add_featured_image' );
}

function xyz_amp_add_featured_image( $content ) {
    if ( has_post_thumbnail() ) {
        // Just add the raw <img /> tag; our sanitizer will take care of it later.
        $image = sprintf( '<p class="xyz-featured-image">%s</p>', get_the_post_thumbnail() );
        $content = $image . $content;
    }
    return $content;
}

Content Width

By default, your theme's $content_width value will be used to determine the size of the amp content well. You can change this:

add_filter( 'amp_content_max_width', 'xyz_amp_change_content_width' );

function xyz_amp_change_content_width( $content_max_width ) {
    return 1200;
}

Template Data

Use the amp_post_template_data filter to override default template data. The following changes the placeholder image used for iframes to a file located in the current theme:

add_filter( 'amp_post_template_data', 'xyz_amp_set_custom_placeholder_image' );

function xyz_set_custom_placeholder_image( $data ) {
    $data[ 'placeholder_image_url' ] = get_stylesheet_directory_uri() . '/images/amp-iframe-placeholder.png';
    return $data;
}

Note: The path must pass the default criteria set out by validate_file and must be somewhere in a subfolder of WP_CONTENT_DIR.

Schema.org (JSON) Metadata

The plugin adds some default metadata to enable "Rich Snippet" support. You can modify this using the amp_post_template_metadata filter. The following changes the type annotation to NewsArticle (from the default BlogPosting) and overrides the default Publisher Logo.

add_filter( 'amp_post_template_metadata', 'xyz_amp_modify_json_metadata', 10, 2 );

function xyz_amp_modify_json_metadata( $metadata, $post ) {
    $metadata['@type'] = 'NewsArticle';

    $metadata['publisher']['logo'] = array(
        '@type' => 'ImageObject',
        'url' => get_template_directory_uri() . '/images/my-amp-metadata-logo.png',
        'height' => 60,
        'width' => 600,
    );

    return $metadata;
}

Template Meta (Author, Date, etc.)

For the meta section of the template (i.e. author, date, taxonomies, etc.), you can override templates for the existing sections, remove them, add new ones.

Example: Override Author Template from Theme

Create a folder in your theme called amp and add a file called meta-author.php with the following:

<li class="xyz-byline">
    <span>Anonymous</span>
</li>

Replace the contents, as needed.

Example: Override Taxonomy Template via filter

This will load the file t/meta-custom-tax.php for the taxonomy section:

add_filter( 'amp_post_template_file', 'xyz_amp_set_custom_tax_meta_template', 10, 3 );

function xyz_amp_set_custom_tax_meta_template( $file, $type, $post ) {
    if ( 'meta-taxonomy' === $type ) {
        $file = dirname( __FILE__ ) . '/t/meta-custom-tax.php';
    }
    return $file;
}

In t/meta-custom-tax.php, you can add something like the following to replace the default category and tags with your custom author taxonomy:

<li class="xyz-tax-authors">
    <?php echo get_the_term_list( $this->get( 'post_id' ), 'xyz-author', '', ', ' ); ?>
</li>
Example: Remove Author from header_meta

This will completely remove the author section:

add_filter( 'amp_post_article_header_meta', 'xyz_amp_remove_author_meta' );

function xyz_amp_remove_author_meta( $meta_parts ) {
    foreach ( array_keys( $meta_parts, 'meta-author', true ) as $key ) {
        unset( $meta_parts[ $key ] );
    }
    return $meta_parts;
}
Example: Add Comment Count to footer_meta

This adds a new section to display the comment count:

add_filter( 'amp_post_article_footer_meta', 'xyz_amp_add_comment_count_meta' );

function xyz_amp_add_comment_count_meta( $meta_parts ) {
    $meta_parts[] = 'xyz-meta-comment-count';
    return $meta_parts;
}

add_filter( 'amp_post_template_file', 'xyz_amp_set_comment_count_meta_path', 10, 3 );

function xyz_amp_set_comment_count_meta_path( $file, $type, $post ) {
    if ( 'xyz-meta-comment-count' === $type ) {
        $file = dirname( __FILE__ ) . '/templates/xyz-meta-comment-count.php';
    }
    return $file;
}

Then, in templates/xyz-meta-comment-count.php:

<li>
    <?php printf( _n( '%d comment', '%d comments', $this->get( 'post' )->comment_count, 'xyz-text-domain' ) ); ?>
</li>

Custom CSS

Rule Additions

If you want to append to the existing CSS rules (e.g. styles for a custom embed handler), you can use the amp_post_template_css action:

add_action( 'amp_post_template_css', 'xyz_amp_my_additional_css_styles' );

function xyz_amp_my_additional_css_styles( $amp_template ) {
    // only CSS here please...
    ?>
    .amp-wp-byline amp-img {
        border-radius: 0; /* we don't want round avatars! */
    }
    .my-custom-class {
        color: blue;
    }
    <?php
}
Completely Override CSS

If you'd prefer to use your own styles, you can either:

  • Create a folder in your theme called amp and add a file called style.php with your custom CSS.
  • Specify a custom template using the amp_post_template_file filter for 'style' === $type. See the "Override" examples in the "Meta" section for examples.

Note: the file should only include CSS, not the <style> opening and closing tag.

Head and Footer

If you want to add stuff to the head or footer of the default AMP template, use the amp_post_template_head and amp_post_template_footer actions.

add_action( 'amp_post_template_footer', 'xyz_amp_add_pixel' );

function xyz_amp_add_pixel( $amp_template ) {
    $post_id = $amp_template->get( 'post_id' );
    ?>
    <amp-pixel src="https://example.com/hi.gif?x=RANDOM"></amp-pixel>
    <?php
}

AMP Endpoint

If you don't want to use the default /amp endpoint, use the amp_query_var filter to change it to anything else.

add_filter( 'amp_query_var' , 'xyz_amp_change_endpoint' );

function xyz_amp_change_endpoint( $amp_endpoint ) {
    return 'foo';
}

Custom Template

If you want complete control over the look and feel of your AMP content, you can override the default template using the amp_post_template_file filter and pass it the path to a custom template:

add_filter( 'amp_post_template_file', 'xyz_amp_set_custom_template', 10, 3 );

function xyz_amp_set_custom_template( $file, $type, $post ) {
    if ( 'single' === $type ) {
        $file = dirname( __FILE__ ) . '/templates/my-amp-template.php';
    }
    return $file;
}

Note: there are some requirements for a custom template:

  • You must trigger the amp_post_template_head action in the <head> section:
do_action( 'amp_post_template_head', $this );
  • You must trigger the amp_post_template_footer action right before the </body> tag:
do_action( 'amp_post_template_footer', $this );
  • Within your amp-custom style tags, you must trigger the amp_post_template_css action:
do_action( 'amp_post_template_css', $this );
  • You must include all required mark-up that isn't already output via the amp_post_template_head action.

Handling Media

By default, the plugin attempts to gracefully handle the following media elements in your content:

  • images (converted from img => amp-img or amp-anim)
  • videos (converted from video => amp-video; Note: Flash is not supported)
  • audio (converted from audio => amp-audio)
  • iframes (converted from iframes => amp-iframes)
  • YouTube, Instagram, Twitter, and Vine oEmbeds and shortcodes (converted from the embed to the matching amp- component)

For additional media content such as custom shortcodes, oEmbeds or manually inserted embeds, ads, etc. there are several customization options available and outlined below.

Do Nothing

If your embeds/media use standard iframes, you can choose to do nothing and let the plugin handle things. They should "just work" in most cases.

the_content filter

All existing hooks on the_content will continue to work. This can be a good or bad thing. Good, because existing plugin integrations will continue to work. Bad, because not all added content may make sense in an AMP context.

You can add additional callbacks to the_content filter to output additional content as needed. Use the is_amp_endpoint() function to check if an AMP version of a post is being viewed. However, we recommend using an Embed Handler instead.

Caveat: with this method, if you add a custom component that requires inclusion of a script, you will need to add that script manually to the template using the amp_post_template_head action.

Update Existing Shortcodes

In your existing shortcode or oEmbed callbacks, you can branch using the is_amp_endpoint() and output customized content for AMP content.

The same caveat about scripts for custom AMP components applies.

Custom Embed Handler

Embed Handlers are helper classes to inject AMP-specific content for your oEmbeds and shortcodes.

Embed Handlers register the embeds they handle using standard WordPress functions such as add_shortcode. For working examples, check out the existing implementations for Instagram, Twitter, etc. as guides to build your own.

While the primary purpose of Embed Handlers is for use with embeds, you can use them for adding AMP-specific the_content callbacks as well.

Step 1: Build the Embed Handler

Your Embed Handler class needs to extend the AMP_Base_Embed_Handler class.

Note: make sure to set proper priorities or remove existing callbacks for your regular content.

In classes/class-amp-related-posts-embed.php:

class XYZ_AMP_Related_Posts_Embed extends AMP_Base_Embed_Handler {
    public function register_embed() {
        // If we have an existing callback we are overriding, remove it.
        remove_filter( 'the_content', 'xyz_add_related_posts' );

        // Add our new callback
        add_filter( 'the_content', array( $this, 'add_related_posts' ) );
    }

    public function unregister_embed() {
        // Let's clean up after ourselves, just in case.
        add_filter( 'the_content', 'xyz_add_related_posts' );
        remove_filter( 'the_content', array( $this, 'add_related_posts' ) );
    }

    public function get_scripts() {
        return array( 'amp-mustache' => 'https://cdn.ampproject.org/v0/amp-mustache-0.1.js' );
    }

    public function add_related_posts( $content ) {
        // See https://github.com/ampproject/amphtml/blob/master/extensions/amp-list/amp-list.md for details on amp-list
        $related_posts_list = '
<amp-list src="https://data.com/articles.json?ref=CANONICAL_URL" width=300 height=200 layout=responsive>
    <template type="amp-mustache">
        <div>
            <amp-img src="{{imageUrl}}" width=50 height=50></amp-img>
            {{title}}
        </div>
    </template>
    <div overflow role=button aria-label="Show more" class="list-overflow">
        Show more
    </div>
</amp-list>';

        $content .= $related_posts_list;

        return $content;
    }
}

Step 2: Load the Embed Handler

add_filter( 'amp_content_embed_handlers', 'xyz_amp_add_related_embed', 10, 2 );

function xyz_amp_add_related_embed( $embed_handler_classes, $post ) {
    require_once( dirname( __FILE__ ) . '/classes/class-amp-related-posts-embed.php' );
    $embed_handler_classes[ 'XYZ_AMP_Related_Posts_Embed' ] = array();
    return $embed_handler_classes;
}

Custom Sanitizer

The name "sanitizer" is a bit of a misnomer. These are primarily used internally in the plugin to make your site's content compatible with the amp spec. This involves stripping unsupported tags and attributes and transforming media elements to their matching amp version (e.g. img => amp-img).

Sanitizers are pretty versatile and, unlike Embed Handlers -- which work with HTML content as a string -- they can be used to manipulate your post's AMP content using PHP's DOM library. We've included an example that shows you how to use a custom sanitizer to inject ads into your content. You can, of course, do many other things such as add related content.

Step 1: Build the Sanitizer

Your sanitizer needs to extend the AMP_Base_Sanitizer. In classes/class-ad-inject-sanitizer.php:

class XYZ_AMP_Ad_Injection_Sanitizer extends AMP_Base_Sanitizer {
    public function sanitize() {
        $body = $this->get_body_node();

        // Build our amp-ad tag
        $ad_node = AMP_DOM_Utils::create_node( $this->dom, 'amp-ad', array(
            // Taken from example at https://github.com/ampproject/amphtml/blob/master/builtins/amp-ad.md
            'width' => 300,
            'height' => 250,
            'type' => 'a9',
            'data-aax_size' => '300x250',
            'data-aax_pubname' => 'test123',
            'data-aax_src' => '302',
        ) );

        // Add a placeholder to show while loading
        $fallback_node = AMP_DOM_Utils::create_node( $this->dom, 'amp-img', array(
            'placeholder' => '',
            'layout' => 'fill',
            'src' => 'https://placehold.it/300X250',
        ) );
        $ad_node->appendChild( $fallback_node );

        // If we have a lot of paragraphs, insert before the 4th one.
        // Otherwise, add it to the end.
        $p_nodes = $body->getElementsByTagName( 'p' );
        if ( $p_nodes->length > 6 ) {
            $p_nodes->item( 4 )->parentNode->insertBefore( $ad_node, $p_nodes->item( 4 ));
        } else {
            $body->appendChild( $ad_node );
        }
    }
}

Step 2: Load the Sanitizer

add_filter( 'amp_content_sanitizers', 'xyz_amp_add_ad_sanitizer', 10, 2 );

function xyz_amp_add_ad_sanitizer( $sanitizer_classes, $post ) {
    require_once( dirname( __FILE__ ) . '/classes/class-ad-inject-sanitizer.php' );
    $sanitizer_classes[ 'XYZ_AMP_Ad_Injection_Sanitizer' ] = array(); // the array can be used to pass args to your sanitizer and accessed within the class via `$this->args`
    return $sanitizer_classes;
}

Extracting Image Dimensions

AMP requires images to have width and height attributes. When these attributes aren't present in an image tag, AMP-WP will attempt to determine them for the image.

Extraction Methods

Concurrent Dimension Extraction - PHP 5.3+ and cURL

If you're using PHP 5.3+ and have the cURL extension installed, AMP-WP will attempt to determine dimensions for all images that need them concurrently. Only the minimum number of bytes required to determine the dimensions for a given image type are retrieved. Dimensions are then cached via transients for subsequent requests. This is the fastest and therefore recommended method.

Sequential Dimension Extraction - PHP 5.2 or no cURL

If you're using PHP 5.2 or do not have the cURL extension installed, AMP-WP will attempt to determine image dimensions sequentially. Only the minimum number of bytes required to determine the dimensions for a given image type are retrieved, but the time it takes to retrieve each image's dimensions sequentially can still add up. Dimensions are then cached via transients for subsequent requests.

Custom Dimension Extraction

You can implement your own image dimension extraction method by adding a callback to the amp_extract_image_dimensions_batch filter.

amp_extract_image_dimensions_batch callback functions take a single argument, $dimensions by convention, which is a map/array of image urls to either an array containing the dimensions of the image at the url (if another callback for the filter was able to determine them), or false if the dimensions have yet to be determined, e.g.

array(
    'http://i0.wp.com/placehold.it/350x150.png' => array(
        'width' => 350,
        'height' => 150,
     ),
     'http://i0.wp.com/placehold.it/1024x768.png' => false,
);

Your custom dimension extraction callback would iterate through the mappings contained in this single argument, determining dimensions via your custom method for all image url keys whose values are not arrays of dimensions, e.g.

function my_custom_dimension_extraction_callback( $dimensions ) {
    foreach ( $dimensions as $url => $value ) {
        // Skip if dimensions have already been determined for this image.
        if ( is_array( $value ) ) {
            continue;                
        }
        $width = <YOUR CUSTOM CODE TO DETERMINE WIDTH>
        $height = <YOUR CUSTOM CODE TO DETERMINE HEIGHT>
        $dimensions[ $url ] = array(
            'width' => $width,
            'height' => $height,
         );
    }

    return $dimensions;

Your callback needs to return $dimensions so that the value either cascades to the next callback that was added to the amp_extract_image_dimensions_batch filter or is returned to the apply_filter() call (if there are no more unprocessed callbacks).

The default callback provided by WP-AMP described above, extract_by_downloading_images, will fire unless explicitly removed, so be sure to remove it from the callback chain if you don't want it to, e.g.

    remove_filter( 'amp_extract_image_dimensions_batch', array( 'AMP_Image_Dimension_Extractor', 'extract_by_downloading_images' ), 999, 1 );

Note that if you previously added a custom dimension extraction callback to the amp_extract_image_dimensions filter, you need to update it to hook into the amp_extract_image_dimensions_batch filter instead and iterate over the key value pairs in the single argument as per the example above.

Analytics

To output proper analytics tags, you can use the amp_post_template_analytics filter:

add_filter( 'amp_post_template_analytics', 'xyz_amp_add_custom_analytics' );
function xyz_amp_add_custom_analytics( $analytics ) {
    if ( ! is_array( $analytics ) ) {
        $analytics = array();
    }

    // https://developers.google.com/analytics/devguides/collection/amp-analytics/
    $analytics['xyz-googleanalytics'] = array(
        'type' => 'googleanalytics',
        'attributes' => array(
            // 'data-credentials' => 'include',
        ),
        'config_data' => array(
            'vars' => array(
                'account' => "UA-XXXXX-Y"
            ),
            'triggers' => array(
                'trackPageview' => array(
                    'on' => 'visible',
                    'request' => 'pageview',
                ),
            ),
        ),
    );

    // https://www.parsely.com/docs/integration/tracking/google-amp.html
    $analytics['xyz-parsely'] = array(
        'type' => 'parsely',
        'attributes' => array(),
        'config_data' => array(
            'vars' => array(
                'apikey' => 'YOUR APIKEY GOES HERE',
            )
        ),
    );

    return $analytics;
}

Each analytics entry must include a unique array key and the following attributes:

  • type: (string) one of the valid vendors for amp-analytics.
  • attributes: (array) any additional valid attributes to add to the amp-analytics element.
  • config_data: (array) the config data to include in the amp-analytics script tag. This is json_encode-d on output.

Custom Post Type Support

By default, the plugin only creates AMP content for posts. You can add support for other post_types using the post_type parameter used when registering the custom post type (assume our post_type is xyz-review):

add_action( 'amp_init', 'xyz_amp_add_review_cpt' );
function xyz_amp_add_review_cpt() {
    add_post_type_support( 'xyz-review', AMP_QUERY_VAR );
}

You'll need to flush your rewrite rules after this.

If you want a custom template for your post type:

add_filter( 'amp_post_template_file', 'xyz_amp_set_review_template', 10, 3 );

function xyz_amp_set_review_template( $file, $type, $post ) {
    if ( 'single' === $type && 'xyz-review' === $post->post_type ) {
        $file = dirname( __FILE__ ) . '/templates/my-amp-review-template.php';
    }
    return $file;
}

We may provide better ways to handle this in the future.

Plugin integrations

Jetpack

Jetpack integration is baked in. More support for things like Related Posts to come.

Parse.ly

Parse.ly's WordPress plugin automatically tracks AMP pages when enabled along with this plugin.

Yoast SEO

If you're using Yoast SEO, check out the companion plugin here: https://github.com/Yoast/yoastseo-amp

Compatibility Issues

The following plugins have been known to cause issues with this plugin:

  • Cloudflare Rocket Loader (modifies the output of the AMP page, which breaks validation.)