From 7fca6f502ffaaccbeda7453ec743625690fdb051 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?R=C3=A9gis=20Hanol?= <regis@hanol.fr>
Date: Mon, 20 Jun 2016 12:35:07 +0200
Subject: [PATCH] fix and improve image downsizing algorithm

---
 app/controllers/uploads_controller.rb | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/app/controllers/uploads_controller.rb b/app/controllers/uploads_controller.rb
index 07fe29de4ac..7eeca37d888 100644
--- a/app/controllers/uploads_controller.rb
+++ b/app/controllers/uploads_controller.rb
@@ -51,8 +51,6 @@ class UploadsController < ApplicationController
     render nothing: true, status: 404
   end
 
-  DOWNSIZE_RATIO ||= 0.8
-
   def create_upload(type, file, url)
     begin
       maximum_upload_size = [SiteSetting.max_image_size_kb, SiteSetting.max_attachment_size_kb].max.kilobytes
@@ -72,20 +70,20 @@ class UploadsController < ApplicationController
 
       return { errors: I18n.t("upload.file_missing") } if tempfile.nil?
 
-      # allow users to upload (not that) large images that will be automatically reduced to allowed size
+      # allow users to upload large images that will be automatically reduced to allowed size
       max_image_size_kb = SiteSetting.max_image_size_kb.kilobytes
       if max_image_size_kb > 0 && FileHelper.is_image?(filename)
-        uploaded_size = File.size(tempfile.path)
-        if 0 < uploaded_size && uploaded_size < maximum_upload_size && Upload.should_optimize?(tempfile.path)
+        if File.size(tempfile.path) >= max_image_size_kb && Upload.should_optimize?(tempfile.path)
           attempt = 2
           allow_animation = type == "avatar" ? SiteSetting.allow_animated_avatars : SiteSetting.allow_animated_thumbnails
           while attempt > 0
             downsized_size = File.size(tempfile.path)
-            break if downsized_size >= uploaded_size || downsized_size < max_image_size_kb
+            break if downsized_size < max_image_size_kb
             image_info = FastImage.new(tempfile.path) rescue nil
             w, h = *(image_info.try(:size) || [0, 0])
             break if w == 0 || h == 0
-            dimensions = "#{(w * DOWNSIZE_RATIO).floor}x#{(h * DOWNSIZE_RATIO).floor}"
+            downsize_ratio = best_downsize_ratio(downsized_size, max_image_size_kb)
+            dimensions = "#{(w * downsize_ratio).floor}x#{(h * downsize_ratio).floor}"
             OptimizedImage.downsize(tempfile.path, tempfile.path, dimensions, filename: filename, allow_animation: allow_animation)
             attempt -= 1
           end
@@ -109,4 +107,14 @@ class UploadsController < ApplicationController
     end
   end
 
+  def best_downsize_ratio(downsized_size, max_image_size)
+    if downsized_size / 9 > max_image_size
+      0.3
+    elsif downsized_size / 3 > max_image_size
+      0.6
+    else
+      0.8
+    end
+  end
+
 end