tests are green and config option added

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    compass (0.11.beta.2.03f4c23)
+    compass (0.11.beta.2.a486129)
       chunky_png (~> 0.12.0)
       sass (>= 3.1.0.alpha.218)
 

lib/compass/configuration.rb

@@ -37,7 +37,8 @@ module Compass
       :line_comments,
       :color_output,
       :preferred_syntax,
-      :disable_warnings
+      :disable_warnings,
+      :sprite_engine
     ].flatten
 
   end

lib/compass/configuration/defaults.rb

@@ -128,6 +128,11 @@ module Compass
       def default_preferred_syntax
         :scss
       end
+      
+      def default_sprite_engine
+        :chunky_png
+      end
+      
       # helper functions
 
       def http_join(*segments)

lib/compass/sass_extensions/sprites/base.rb

@@ -1,4 +1,5 @@
 require 'compass/sass_extensions/sprites/image'
+require 'compass/sass_extensions/sprites/engines/chunky_png_engine'
 module Compass
   module SassExtensions
     module Sprites
@@ -12,21 +13,8 @@ module Compass
           new(sprites, path, name, context, kwargs)
         end
 
-      
         def require_engine!
-          begin
+          self.class.send(:include, eval("::Compass::SassExtensions::Sprites::#{modulize}Engine"))
-            require 'rmagick'
-            require 'compass/sass_extensions/sprites/engines/rmagick_engine'
-            self.class.send(:include, ::Compass::SassExtensions::Sprites::RmagickEngine)
-          rescue LoadError
-            require 'compass/sass_extensions/sprites/engines/chunky_png_engine'
-            begin
-              require 'oily_png'
-            rescue LoadError
-              require 'chunky_png'
-            end
-            self.class.send(:include, ::Compass::SassExtensions::Sprites::ChunkyPngEngine)
-          end
         end
       
         # Changing this string will invalidate all previously generated sprite images.
@@ -111,7 +99,6 @@ module Compass
         end
 
         def generation_required?
-          puts !File.exists?(filename) || outdated?
           !File.exists?(filename) || outdated?
         end
 
@@ -169,6 +156,13 @@ module Compass
             super
           end
         end
+        
+        private 
+        
+        def modulize
+          @modulize ||= Compass::configuration.sprite_engine.to_s.scan(/([^_.]+)/).flatten.map {|chunk| "#{chunk[0].chr.upcase}#{chunk[1..-1]}" }.join
+        end
+        
       end
     end
   end

lib/compass/sass_extensions/sprites/engines/chunky_png_engine.rb

@@ -1,7 +1,14 @@
+begin
+  require 'oily_png'
+rescue LoadError
+  require 'chunky_png'
+end
+
 module Compass
   module SassExtensions
     module Sprites
       module ChunkyPngEngine
+        
         # Returns a PNG object
         def construct_sprite
           #require_png_library!

lib/compass/sass_extensions/sprites/engines/rmagick_engine.rb

@@ -1,41 +0,0 @@
-module Compass
-  module SassExtensions
-    module Sprites
-      module RmagickEngine
-        class ::Magick::Image
-          alias :save :write
-        end
-        
-        def composite_images(dest_image, src_image, x, y)
-          width = [src_image.columns + x, dest_image.columns].max
-          height = [src_image.rows + y, dest_image.rows].max
-          image = Magick::Image.new(width, height) {self.background_color = 'none'}
-          image.composite!(dest_image, 0, 0, Magick::CopyCompositeOp)
-          image.composite!(src_image, x, y, Magick::CopyCompositeOp)
-          image
-        end
-        
-        # Returns a PNG object
-        def construct_sprite
-          output_png = Magick::Image.new(width, height)
-          output_png.background_color = 'none'
-          output_png.format = 'PNG24'
-          images.each do |image|
-            input_png = Magick::Image.read(image.file).first
-            if image.repeat == "no-repeat"
-              output_png = composite_images(output_png, input_png, image.left, image.top)
-            else
-              x = image.left - (image.left / image.width).ceil * image.width
-              while x < width do
-                output_png = composite_images(output_png, input_png, x, image.top)
-                #output_png.composite!(input_png, x, image.top, Magick::CopyCompositeOp)
-                x += image.width
-              end
-            end
-          end
-          output_png
-        end
-      end
-    end
-  end
-end