Adding support for calculating JPG dimensions

lib/compass/sass_extensions/functions/image_size.rb

@@ -1,34 +1,99 @@
 module Compass::SassExtensions::Functions::ImageSize
-  def image_width(image_file)    
-    width = compute_size(image_file).first
+  def image_width(image_file)
+    image_path = real_path(image_file)
+    width = ImageProperties.new(image_path).size.first
     Sass::Script::Number.new(width,["px"])
   end
-  
+
   def image_height(image_file)
-    height = compute_size(image_file).last
+    image_path = real_path(image_file)
+    height = ImageProperties.new(image_path).size.last
     Sass::Script::Number.new(height, ["px"])
   end
-  
+
 private
-  # Returns an array [width,height] containing image dimensions
-  def compute_size(image_path)
-    path = image_path.value
+  def real_path(image_file)
+    path = image_file.value
     # Compute the real path to the image on the file stystem if the images_dir is set.
-     real_path = if Compass.configuration.images_dir
-       File.join(Compass.configuration.project_path, Compass.configuration.images_dir, path)
-     else
-       File.join(Compass.configuration.project_path, path)
-     end
-    case real_path
-    when /\.png$/i
-      IO.read(real_path)[0x10..0x18].unpack('NN')
-    when /\.gif$/i
-      IO.read(real_path)[6..10].unpack('SS')
-    when /\.jpe?g$/i
-      # FIXME jpgs are not straightforward
-      raise Compass::Error, "JPEG files are not supported yet."      
+    if Compass.configuration.images_dir
+      File.join(Compass.configuration.project_path, Compass.configuration.images_dir, path)
     else
-      raise Compass::Error, "File is either not an image, or is not supported."
-    end    
-  end  
+      File.join(Compass.configuration.project_path, path)
+    end
+  end
+
+  class ImageProperties
+    def initialize(file)
+      @file = file
+      @file_type = File.extname(@file)[1..-1]
+    end
+
+    def size
+      @dimensions ||=  send("get_size_for_#{@file_type}")
+    end
+
+  private
+    def get_size_for_png
+      IO.read(@file)[0x10..0x18].unpack('NN')
+    end
+
+    def get_size_for_gif
+      size = IO.read(@file)[6..10].unpack('SS')
+      size.inspect
+    end
+
+    def get_size_for_bmp
+      d = IO.read(@file)[14..28]
+      d[0] == 40 ? d[4..-1].unpack('LL') : d[4..8].unpack('SS')
+    end
+
+    def get_size_for_jpg
+      get_size_for_jpeg
+    end
+
+    def get_size_for_jpeg
+      jpeg = JPEG.new(@file)
+      [jpeg.width, jpeg.height]
+    end
+  end
+
+  class JPEG
+    attr_reader :width, :height, :bits
+
+    def initialize(file)
+      if file.kind_of? IO
+        examine(file)
+      else
+        File.open(file, 'rb') { |io| examine(io) }
+      end
+    end
+
+  private
+    def examine(io)
+      raise 'malformed JPEG' unless io.getc == 0xFF && io.getc == 0xD8 # SOI
+
+      class << io
+        def readint; (readchar << 8) + readchar; end
+        def readframe; read(readint - 2); end
+        def readsof; [readint, readchar, readint, readint, readchar]; end
+        def next
+          c = readchar while c != 0xFF
+          c = readchar while c == 0xFF
+          c
+        end
+      end
+
+      while marker = io.next
+        case marker
+          when 0xC0..0xC3, 0xC5..0xC7, 0xC9..0xCB, 0xCD..0xCF # SOF markers
+            length, @bits, @height, @width, components = io.readsof
+            raise 'malformed JPEG' unless length == 8 + components * 3
+          when 0xD9, 0xDA:  break # EOI, SOS
+          when 0xFE:        @comment = io.readframe # COM
+          when 0xE1:        io.readframe # APP1, contains EXIF tag
+          else              io.readframe # ignore frame
+        end
+      end
+    end
+end
 end