Preserve chronological order in gapless gallery rows

_plugins/gallery_items.rb

@@ -1,6 +1,53 @@
 require 'nokogiri'
 
 module GalleryItems
+  JPEG_START_OF_FRAME = [0xC0, 0xC1, 0xC2, 0xC3, 0xC5, 0xC6, 0xC7,
+                         0xC9, 0xCA, 0xCB, 0xCD, 0xCE, 0xCF].freeze
+
+  # Read just the dimensions from a local JPEG. The rendered gallery needs
+  # aspect ratios to size each chronological pair without cropping either photo.
+  def jpeg_dimensions(path)
+    File.open(path, 'rb') do |file|
+      return nil unless file.read(2) == "\xFF\xD8".b
+
+      while (prefix = file.read(1))
+        next unless prefix.getbyte(0) == 0xFF
+
+        marker = file.read(1)&.getbyte(0)
+        break unless marker
+        next if marker == 0xFF || marker == 0x01 || (0xD0..0xD7).cover?(marker)
+        break if marker == 0xD9 || marker == 0xDA
+
+        size = file.read(2)&.unpack1('n')
+        break unless size && size >= 2
+        if JPEG_START_OF_FRAME.include?(marker)
+          dimensions = file.read(5)
+          return nil unless dimensions&.length == 5
+
+          height, width = dimensions.byteslice(1, 4).unpack('n2')
+          return [width, height] if width.positive? && height.positive?
+          return nil
+        end
+        file.seek(size - 2, IO::SEEK_CUR)
+      end
+    end
+    nil
+  rescue Errno::ENOENT, EOFError
+    nil
+  end
+
+  def gallery_image_ratio(content)
+    image = Nokogiri::HTML::DocumentFragment.parse(content).at_css('img')
+    source = image&.[]('src')
+    return 1.5 unless source&.start_with?('/img/arts/')
+
+    path = File.join(File.expand_path('..', __dir__), source.delete_prefix('/'))
+    width, height = jpeg_dimensions(path)
+    return 1.5 unless width && height
+
+    (width.to_f / height).round(4)
+  end
+
   # Uploaded batches share one source document, but each photo is a gallery item.
   # Keeping this at render time also fixes batches that have already been published.
   def gallery_items(content)

_sass/_layout.scss

@@ -227,16 +227,22 @@ hr {
 }
 
 .art .post-list {
-  column-count: 2;
-  column-gap: $spacing-unit;
+  .gallery-row {
+    display: flex;
+    gap: $spacing-unit;
+    align-items: flex-start;
+    list-style: none;
+    margin: 0 0 $spacing-unit;
 
     > li {
-    display: inline-block;
-    width: 100%;
-    margin-top: 0;
-    margin-bottom: $spacing-unit;
-    break-inside: avoid;
-    -webkit-column-break-inside: avoid;
+      flex: var(--photo-ratio) 1 0;
+      min-width: 0;
+      margin: 0;
+    }
+
+    > li:only-child {
+      flex: 0 0 calc((100% - #{$spacing-unit}) / 2);
+    }
   }
 
   .post-content > p:last-child {
@@ -249,11 +255,17 @@ hr {
     height: auto;
     margin: 0;
     // Reserve space before lazy images load, then use their natural proportions.
-    aspect-ratio: auto 3 / 2;
+    aspect-ratio: auto var(--photo-ratio, 3 / 2);
   }
 
   @include media-query($on-palm) {
-    column-count: 1;
+    .gallery-row {
+      display: block;
+
+      > li {
+        margin-bottom: $spacing-unit;
+      }
+    }
   }
 }
 

art.html

@@ -28,14 +28,17 @@ wide_gallery: true
     </details>
   </div>
 
-  <ul class="post-list">
+  <div class="post-list">
+    {% assign gallery_index = 0 %}
     {% for post in site.art reversed %}
       {% if post.published == false %}
         {% continue %}
       {% endif %}
       {% assign items = post.content | markdownify | lazy_images | gallery_items %}
       {% for item in items %}
-      <li class='lang-{% if post.lang %}{{ post.lang }}{% else %}en{% endif %}'>
+      {% assign row_position = gallery_index | modulo: 2 %}
+      {% if row_position == 0 %}<ul class="gallery-row">{% endif %}
+      <li class='lang-{% if post.lang %}{{ post.lang }}{% else %}en{% endif %}' style='--photo-ratio: {{ item | gallery_image_ratio }}'>
         <article class='post-content'>
           {% if post.anchor and forloop.first %}
           <span id='{{ post.title }}'></span>
@@ -43,9 +46,13 @@ wide_gallery: true
           {{ item }}
         </article>
       </li>
+      {% assign gallery_index = gallery_index | plus: 1 %}
+      {% assign row_position = gallery_index | modulo: 2 %}
+      {% if row_position == 0 %}</ul>{% endif %}
       {% endfor %}
     {% endfor %}
-  </ul>
+    {% if row_position == 1 %}</ul>{% endif %}
+  </div>
 
   <p class="rss-subscribe">subscribe <a href="{{ "/feed.xml" | prepend: site.baseurl }}">via rss</a></p>
 

scripts/tests/gallery_items_test.rb

@@ -27,4 +27,10 @@ single = '<p><img src="/img/arts/uploads/batch/00.jpg"></p>'
 raise 'Single photo changed' unless renderer.gallery_items(single) == [single]
 legacy = '<p><img src="/img/old.jpg"></p><p>Existing artwork content</p>'
 raise 'Legacy artwork changed' unless renderer.gallery_items(legacy) == [legacy]
+
+portrait = '<img src="/img/arts/dresden-prague-iran-2024/Prague_000512360030.jpg">'
+landscape = '<img src="/img/arts/uploads/5e085e7d10edc54172e7b5c47d22fe532edec19c879a8d566667d3c3c1bb3d96/00.jpg">'
+raise 'Portrait ratio incorrect' unless renderer.gallery_image_ratio(portrait) < 1
+raise 'Landscape ratio incorrect' unless renderer.gallery_image_ratio(landscape) > 1
+raise 'Video fallback ratio incorrect' unless renderer.gallery_image_ratio('<video></video>') == 1.5
 puts 'Gallery item regression checks passed'