add image cropping support

app/logical/danbooru_image_resizer.rb

@@ -5,6 +5,7 @@ module DanbooruImageResizer
   THUMBNAIL_OPTIONS = { size: :down, linear: false, auto_rotate: false, export_profile: SRGB_PROFILE }
   # http://jcupitt.github.io/libvips/API/current/VipsForeignSave.html#vips-jpegsave
   JPEG_OPTIONS = { background: 255, strip: true, interlace: true, optimize_coding: true }
+  CROP_OPTIONS = { linear: false, auto_rotate: false, export_profile: SRGB_PROFILE, crop: :attention }
 
   # XXX libvips-8.4 on Debian doesn't support the `Vips::Image.thumbnail` method.
   # On 8.4 we have to shell out to vipsthumbnail instead. Remove when Debian supports 8.5.
@@ -16,6 +17,14 @@ module DanbooruImageResizer
     end
   end
 
+  def self.crop(file, length, quality = 90)
+    if Vips.at_least_libvips?(8, 5)
+      crop_ruby(file, length, quality)
+    else
+      crop_shell(file, length, quality)
+    end    
+  end
+
   # https://github.com/jcupitt/libvips/wiki/HOWTO----Image-shrinking
   # http://jcupitt.github.io/libvips/API/current/Using-vipsthumbnail.md.html
   def self.resize_ruby(file, width, height, resize_quality)
@@ -26,6 +35,14 @@ module DanbooruImageResizer
     output_file
   end
 
+  def self.crop_ruby(file, length, resize_quality)
+    output_file = Tempfile.new
+    resized_image = Vips::Image.thumbnail(file.path, length, height: length, **CROP_OPTIONS)
+    resized_image.jpegsave(output_file.path, Q: resize_quality, **JPEG_OPTIONS)
+
+    output_file
+  end
+
   def self.resize_shell(file, width, height, quality)
     output_file = Tempfile.new(["resize", ".jpg"])
 
@@ -47,4 +64,25 @@ module DanbooruImageResizer
 
     output_file
   end
+
+  def self.crop_shell(file, length, quality)
+    output_file = Tempfile.new(["crop", ".jpg"])
+
+    # --size=WxH will upscale if the image is smaller than the target size.
+    # Fix the target size so that it's not bigger than the image.
+    image = Vips::Image.new_from_file(file.path)
+
+    arguments = [
+      file.path,
+      "--eprofile=#{SRGB_PROFILE}",
+      "--crop=none",
+      "--size=#{length}",
+      "--format=#{output_file.path}[Q=#{quality},background=255,strip,interlace,optimize_coding]"
+    ]
+
+    success = system("vipsthumbnail", *arguments)
+    raise RuntimeError, "vipsthumbnail failed (exit status: #{$?.exitstatus})" if !success
+
+    output_file
+  end
 end