Adding Attachment#geometry to get file's dimension

Fixes #768

lib/paperclip/attachment.rb

@@ -319,6 +319,11 @@ module Paperclip
       instance.send(getter) if responds || attr.to_s == "file_name"
     end
 
+    # Returns a geometry object which you can get the image's dimension.
+    def geometry(style = :original)
+      Geometry.from_file(path(style))
+    end
+
     private
 
     def path_option

lib/paperclip/geometry.rb

@@ -11,6 +11,11 @@ module Paperclip
       @modifier = modifier
     end
 
+    # Returns the equality based on height, width, and modifier
+    def ==(other)
+      height == other.height && width == other.width && modifier == other.modifier
+    end
+
     # Uses ImageMagick to determing the dimensions of a file, passed in as either a
     # File or path.
     # NOTE: (race cond) Do not reassign the 'file' variable inside this method as it is likely to be

test/attachment_test.rb

@@ -1158,4 +1158,19 @@ class AttachmentTest < Test::Unit::TestCase
     end
   end
 
+  context "attachment's geometry" do
+    setup do
+      rebuild_model
+      @dummy = Dummy.new
+      @file = File.new(File.join(File.dirname(__FILE__), "fixtures", "5k.png"), 'rb')
+      @dummy.avatar = @file
+      @dummy.save!
+      @attachment = @dummy.avatar
+      @geometry = Paperclip::Geometry.from_file(@file.path)
+    end
+
+    should "return a correct geometry object" do
+      assert_equal @geometry, @attachment.geometry
+    end
+  end
 end