Added a new Sass function called image_url() that can be used instead of url() to link to an image relative to the images directory according to the compass project configuration.

lib/compass/configuration.rb

@@ -5,13 +5,15 @@ module Compass
     include Singleton
 
     ATTRIBUTES = [
+      :project_type,
       :project_path,
       :css_dir,
       :sass_dir,
       :images_dir,
       :javascripts_dir,
       :output_style,
-      :environment
+      :environment,
+      :http_images_path
     ]
 
     attr_accessor *ATTRIBUTES
@@ -77,6 +79,14 @@ module Compass
       "images"
     end
 
+    def default_http_images_path
+      "/#{images_dir}"
+    end
+
+    def comment_for_http_images_path
+      "# To enable relative image paths using the images_url() function:\n# http_images_path = :relative\n"
+    end
+
     def default_output_style
       if environment == :development
         :expanded
@@ -98,6 +108,9 @@ module Compass
       contents << "\n" if required_libraries.any?
       ATTRIBUTES.each do |prop|
         value = send(prop)
+        if respond_to?("comment_for_#{prop}")
+          contents << send("comment_for_#{prop}")
+        end
         unless value.nil?
           contents << %Q(#{prop} = #{value.inspect}\n)
         end

lib/sass_extensions.rb

@@ -2,6 +2,7 @@ require 'sass'
 
 module Sass::Script::Functions
   COMMA_SEPARATOR = /\s*,\s*/
+
   def nest(*arguments)
     nested = arguments.map{|a| a.value}.inject do |memo,arg|
       ancestors = memo.split(COMMA_SEPARATOR)
@@ -10,4 +11,19 @@ module Sass::Script::Functions
     end
     Sass::Script::String.new(nested)
   end
+
+  def image_url(path)
+    http_images_path = if Compass.configuration.http_images_path == :relative
+      if (target_css_file = options[:css_filename])
+        images_path = File.join(Compass.configuration.project_path, Compass.configuration.images_dir)
+        Pathname.new(images_path).relative_path_from(Pathname.new(File.dirname(target_css_file))).to_s
+      else
+        nil
+      end
+    else
+      Compass.configuration.http_images_path
+    end
+    path = "#{http_images_path}/#{path}" if http_images_path
+    Sass::Script::String.new("url(#{path})")
+  end
 end