Adding image_height and image_width functions

lib/compass/sass_extensions/functions.rb

@@ -1,7 +1,7 @@
 module Compass::SassExtensions::Functions
 end
 
-%w(selectors enumerate urls display inline_image color_stop font_files).each do |func|
+%w(selectors enumerate urls display inline_image image_size color_stop font_files).each do |func|
   require "compass/sass_extensions/functions/#{func}"
 end
 
@@ -11,6 +11,7 @@ module Sass::Script::Functions
   include Compass::SassExtensions::Functions::Urls
   include Compass::SassExtensions::Functions::Display
   include Compass::SassExtensions::Functions::InlineImage
+  include Compass::SassExtensions::Functions::ImageSize
   include Compass::SassExtensions::Functions::ColorStop
   include Compass::SassExtensions::Functions::FontFiles
 end

lib/compass/sass_extensions/functions/image_size.rb

@@ -0,0 +1,34 @@
+module Compass::SassExtensions::Functions::ImageSize
+  def image_width(image_file)    
+    width = compute_size(image_file).first
+    Sass::Script::Number.new(width,["px"])
+  end
+  
+  def image_height(image_file)
+    height = compute_size(image_file).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
+    # 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."      
+    else
+      raise Compass::Error, "File is either not an image, or is not supported."
+    end    
+  end  
+end