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



11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
 
# 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, '', 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