Resize images by area instead of fixed dimensions (#8083)

To improve the way super tall or super ride images are treated, the
numbers remain the same, 1280x1280 and 400x400, but if an image
is less in one dimension than the other, the other can become larger

Thanks to @WAHa_06x36@mastodon.social for the tip

app/javascript/mastodon/utils/resize_image.js

 import EXIF from 'exif-js';
 
-const MAX_IMAGE_DIMENSION = 1280;
+const MAX_IMAGE_PIXELS = 1638400; // 1280x1280px
 
 const getImageUrl = inputFile => new Promise((resolve, reject) => {
   if (window.URL && URL.createObjectURL) {
@@ -73,18 +73,8 @@ const processImage = (img, { width, height, orientation, type = 'image/png' }) =
 const resizeImage = (img, type = 'image/png') => new Promise((resolve, reject) => {
   const { width, height } = img;
 
-  let newWidth, newHeight;
-
-  if (width > height) {
-    newHeight = height * MAX_IMAGE_DIMENSION / width;
-    newWidth  = MAX_IMAGE_DIMENSION;
-  } else if (height > width) {
-    newWidth  = width * MAX_IMAGE_DIMENSION / height;
-    newHeight = MAX_IMAGE_DIMENSION;
-  } else {
-    newWidth  = MAX_IMAGE_DIMENSION;
-    newHeight = MAX_IMAGE_DIMENSION;
-  }
+  const newWidth  = Math.round(Math.sqrt(MAX_IMAGE_PIXELS * (width / height)));
+  const newHeight = Math.round(Math.sqrt(MAX_IMAGE_PIXELS * (height / width)));
 
   getOrientation(img, type)
     .then(orientation => processImage(img, {
@@ -104,7 +94,7 @@ export default inputFile => new Promise((resolve, reject) => {
   }
 
   loadImage(inputFile).then(img => {
-    if (img.width < MAX_IMAGE_DIMENSION && img.height < MAX_IMAGE_DIMENSION) {
+    if (img.width * img.height < MAX_IMAGE_PIXELS) {
       resolve(inputFile);
       return;
     }

app/models/media_attachment.rb

@@ -32,12 +32,12 @@ class MediaAttachment < ApplicationRecord
 
   IMAGE_STYLES = {
     original: {
-      geometry: '1280x1280>',
+      pixels: 1_638_400, # 1280x1280px
       file_geometry_parser: FastGeometryParser,
     },
 
     small: {
-      geometry: '400x400>',
+      pixels: 160_000, # 400x400px
       file_geometry_parser: FastGeometryParser,
     },
   }.freeze
@@ -152,7 +152,7 @@ class MediaAttachment < ApplicationRecord
       elsif VIDEO_MIME_TYPES.include? f.file_content_type
         [:video_transcoder]
       else
-        [:thumbnail]
+        [:lazy_thumbnail]
       end
     end
   end

lib/paperclip/lazy_thumbnail.rb

@@ -5,8 +5,14 @@ module Paperclip
     def make
       return File.open(@file.path) unless needs_convert?
 
-      min_side = [@current_geometry.width, @current_geometry.height].min
-      options[:geometry] = "#{min_side.to_i}x#{min_side.to_i}#" if @target_geometry.square? && min_side < @target_geometry.width
+      if options[:geometry]
+        min_side = [@current_geometry.width, @current_geometry.height].min.to_i
+        options[:geometry] = "#{min_side}x#{min_side}#" if @target_geometry.square? && min_side < @target_geometry.width
+      elsif options[:pixels]
+        width  = Math.sqrt(options[:pixels] * (@current_geometry.width.to_f / @current_geometry.height.to_f)).round.to_i
+        height = Math.sqrt(options[:pixels] * (@current_geometry.height.to_f / @current_geometry.width.to_f)).round.to_i
+        options[:geometry] = "#{width}x#{height}>"
+      end
 
       Paperclip::Thumbnail.make(file, options, attachment)
     end
@@ -18,7 +24,8 @@ module Paperclip
     end
 
     def needs_different_geometry?
-      !@target_geometry.nil? && @current_geometry.width != @target_geometry.width && @current_geometry.height != @target_geometry.height
+      (options[:geometry] && @current_geometry.width != @target_geometry.width && @current_geometry.height != @target_geometry.height) ||
+        (options[:pixels] && @current_geometry.width * @current_geometry.height > options[:pixels])
     end
 
     def needs_different_format?

spec/models/media_attachment_spec.rb

@@ -129,9 +129,9 @@ RSpec.describe MediaAttachment, type: :model do
       expect(media.file.meta["original"]["width"]).to eq 600
       expect(media.file.meta["original"]["height"]).to eq 400
       expect(media.file.meta["original"]["aspect"]).to eq 1.5
-      expect(media.file.meta["small"]["width"]).to eq 400
-      expect(media.file.meta["small"]["height"]).to eq 267
-      expect(media.file.meta["small"]["aspect"]).to eq 400.0/267
+      expect(media.file.meta["small"]["width"]).to eq 490
+      expect(media.file.meta["small"]["height"]).to eq 327
+      expect(media.file.meta["small"]["aspect"]).to eq 490.0/327
     end
   end