Module: Jekyll::AmpFilter

Defined in:
lib/jekyll/amp_filter.rb

Instance Method Summary collapse

Instance Method Details

#amp_images(input, responsive = true, wi = nil, he = nil) ⇒ Object

Filter for HTML 'img' elements. Converts elements to 'amp-img' and adds additional attributes Parameters:

input       - the content of the post
responsive  - boolean, whether to add layout=responsive, true by default

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# File 'lib/jekyll/amp_filter.rb', line 11

def amp_images(input, responsive = true, wi = nil, he = nil)
  doc = Nokogiri::HTML.fragment(input);
  # Add width and height to img elements lacking them
  doc.css('img:not([width])').each do |image|
    if wi && he
      image['width']  = wi
      image['height'] = he
    else
      if image['src'].start_with?('http://', 'https://')
        src = image['src']
      else
        # FastImage doesn't seem to handle local paths when used with Jekyll
        # so let's just force the path
        src = File.join(Dir.pwd, '_site', image['src'])
      end
      # Jekyll generates static assets after the build process.
      # This causes problems when trying to determine the dimensions of a locally stored image.
      # For now, the only solution is to skip the build and generate the AMP files after the site has beem successfully built.
      # TODO: find a better solution.
      begin
        size = FastImage.size(src)
        image['width']  = size[0]
        image['height'] = size[1]
      rescue Exception => e
        puts 'Unable to get image dimensions for "' + src + '". For local files, build the site with \'--skip-initial-build\' for better results. [Error: ' + e.to_s + ']'
      end
    end
  end
  # Change 'img' elements to 'amp-img', add responsive attribute when needed
  doc.css('img').each do |image|
    image.name = "amp-img"

    image['layout'] = "responsive" if responsive
  end

  # Picture elements are not accepted in amp pages, convert them to amp-img
  #<picture>
  #   <source srcset="mdn-logo-wide.webp" type="image/webp">
  #   <source srcset="mdn-logo-wide.png" media="(min-width: 600px)">
  #   <img src="mdn-logo-narrow.png" alt="MDN">
  #</picture>
  # Move amp-img elements inside picture elements outside of it and remove picture elements
  doc.css('picture').each do |picture|
    # Get img element from picture
    amp_img = picture.css('amp-img')
    picture.add_next_sibling(amp_img) unless amp_img.empty?

    # Remove picture element
    picture.remove
  end

  # Added <img /> tag wrapped with <noscript /> in case js is not enabled
  # but image will still show up. The element would look like this:
  # <amp-img ...>
  #    <noscript>
  #        <img ... />
  #    </noscript>
  # </ampimg ...>
  # Duplicate amp-img, remove layout attribut, wrap it with noscript, and add
  # it as amp-img child
  doc.css('amp-img').each do |amp_img|
    noscript = Nokogiri::XML::Node.new "noscript", doc

    noscript_img = amp_img.dup
    noscript_img.remove_attribute('layout')
    noscript_img.name = 'img'

    noscript.add_child(noscript_img)

    amp_img.add_child(noscript)
  end

  # Return the html as plaintext string
  doc.to_s
end