Add blurhash (#10630)

* Add blurhash

* Use fallback color for spoiler when blurhash missing

* Federate the blurhash and accept it as long as it's at most 5x5

* Display unknown media attachments as blurhash placeholders

* Improve style of embed actions and spoiler button

* Change blurhash resolution from 3x3 to 4x4

* Improve dependency definitions

* Fix code style issues

app/models/media_attachment.rb

@@ -18,6 +18,7 @@
 #  account_id          :bigint(8)
 #  description         :text
 #  scheduled_status_id :bigint(8)
+#  blurhash            :string
 #
 
 class MediaAttachment < ApplicationRecord
@@ -32,6 +33,11 @@ class MediaAttachment < ApplicationRecord
   VIDEO_MIME_TYPES             = ['video/webm', 'video/mp4', 'video/quicktime'].freeze
   VIDEO_CONVERTIBLE_MIME_TYPES = ['video/webm', 'video/quicktime'].freeze
 
+  BLURHASH_OPTIONS = {
+    x_comp: 4,
+    y_comp: 4,
+  }.freeze
+
   IMAGE_STYLES = {
     original: {
       pixels: 1_638_400, # 1280x1280px
@@ -41,6 +47,7 @@ class MediaAttachment < ApplicationRecord
     small: {
       pixels: 160_000, # 400x400px
       file_geometry_parser: FastGeometryParser,
+      blurhash: BLURHASH_OPTIONS,
     },
   }.freeze
 
@@ -53,6 +60,8 @@ class MediaAttachment < ApplicationRecord
       },
       format: 'png',
       time: 0,
+      file_geometry_parser: FastGeometryParser,
+      blurhash: BLURHASH_OPTIONS,
     },
   }.freeze
 
@@ -166,11 +175,11 @@ class MediaAttachment < ApplicationRecord
 
     def file_processors(f)
       if f.file_content_type == 'image/gif'
-        [:gif_transcoder]
+        [:gif_transcoder, :blurhash_transcoder]
       elsif VIDEO_MIME_TYPES.include? f.file_content_type
-        [:video_transcoder]
+        [:video_transcoder, :blurhash_transcoder]
       else
-        [:lazy_thumbnail]
+        [:lazy_thumbnail, :blurhash_transcoder]
       end
     end
   end