Added utilities/color/contrast module. Added contrasted mixin and

get_contrast_yiq function.

frameworks/compass/stylesheets/compass/_utilities.scss

@@ -1,3 +1,4 @@
+@import "utilities/color";
 @import "utilities/general";
 @import "utilities/sprites";
 @import "utilities/tables";

frameworks/compass/stylesheets/compass/utilities/_color.scss

@@ -0,0 +1 @@
+@import "color/contrast";

frameworks/compass/stylesheets/compass/utilities/color/_contrast.scss

@@ -0,0 +1,8 @@
+$contrasted-default-dark:   #000;
+$contrasted-default-light:  #fff;
+
+// Sets the specified background color and calculates a dark or light contrasted text color.
+@mixin contrasted($bg, $dark:$contrasted-default-dark, $light:$contrasted-default-light){
+  background-color: $bg;
+  color: get_contrast_yiq($bg, $dark, $light);
+}

lib/compass/sass_extensions/functions/colors.rb

@@ -41,6 +41,13 @@ module Compass::SassExtensions::Functions::Colors
     Sass::Script::String.new("##{alphastr}#{color.send(:hex_str)[1..-1]}".upcase)
   end
   
+  # Calculates the contrast of a color using the YIQ algorithm
+  # Returns one of either a dark or light color based on the YIQ
+  def get_contrast_yiq(color, dark = Sass::Script::Color.new([0,0,0]), light = Sass::Script::Color.new([255,255,255]))
+    yiq = ( (color.red*299) + (color.green*587) + (color.blue*114) ) / 1000;
+    yiq >= 128 ? dark : light
+  end
+
   private
   def scale_color_value(value, amount)
     if amount > 0

test/sass_extensions_test.rb

@@ -89,6 +89,11 @@ class SassExtensionsTest < Test::Unit::TestCase
     assert_equal "true", evaluate("blank(-compass-space-list(' '))")
   end
   
+  def test_get_contrast
+    assert_equal "white", evaluate("get_contrast_yiq(#000)")
+    assert_equal "black", evaluate("get_contrast_yiq(#fff)")
+  end
+
 protected
   def evaluate(value)
     Sass::Script::Parser.parse(value, 0, 0).perform(Sass::Environment.new).to_s