adjust & scale lightness and saturation

doc-src/content/reference/compass/helpers.haml

@@ -18,6 +18,8 @@ layout: core
   
   All Helpers:
   
+  * [adjust-lightness()](/docs/reference/compass/helpers/colors/#adjust-lightness)
+  * [adjust-saturation()](/docs/reference/compass/helpers/colors/#adjust-saturation)
   * [append-selector()](/docs/reference/compass/helpers/selectors/#append-selector)
   * [color-stops()](/docs/reference/compass/helpers/color-stops/)
   * [elements-of-type()](/docs/reference/compass/helpers/display/)
@@ -32,4 +34,6 @@ layout: core
   * [inline-image()](/docs/reference/compass/helpers/inline-data/#inline-image)
   * [nest()](/docs/reference/compass/helpers/selectors/#nest)
   * [stylesheet-url()](/docs/reference/compass/helpers/urls/#stylesheet-url)
+  * [scale-lightness()](/docs/reference/compass/helpers/colors/#scale-lightness)
+  * [scale-saturation()](/docs/reference/compass/helpers/colors/#scale-saturation)
 

doc-src/content/reference/compass/helpers/colors.haml

@@ -0,0 +1,53 @@
+--- 
+title: Compass Color Helpers
+crumb: Colors
+framework: compass
+meta_description: Helper function for colors.
+layout: core
+classnames:
+  - reference
+  - core
+  - helpers
+---
+%h1 Compass Color Helpers
+%p
+  These color functions are useful for creating generic libraries that have to accept a
+  range of inputs. For more color functions see
+  <a href="http://sass-lang.com/docs/yardoc/Sass/Script/Functions.html">the sass reference
+  documentation</a>
+
+#adjust-lightness.helper
+  %h3
+    %a(href="#adjust-lightness")
+      adjust-lightness(<span class="arg">$color</span>, <span class="arg">$amount</span>)
+  .details
+    %p
+      Adds <code>$amount</code> to <code>$color</code>'s lightness value. <code>$amount</code>
+      can be negative.
+
+#adjust-saturation.helper
+  %h3
+    %a(href="#adjust-saturation")
+      adjust-saturation(<span class="arg">$color</span>, <span class="arg">$amount</span>)
+  .details
+    %p
+      Adds <code>$amount</code> to <code>$color</code>'s saturation value. <code>$amount</code>
+      can be negative.
+
+#scale-lightness.helper
+  %h3
+    %a(href="#scale-lightness")
+      scale-lightness(<span class="arg">$color</span>, <span class="arg">$amount</span>)
+  .details
+    %p
+      Scales <code>$color</code>'s lightness value by <code>$amount</code>.
+      <code>$amount</code> can be negative.
+
+#scale-saturation.helper
+  %h3
+    %a(href="#scale-saturation")
+      scale-saturation(<span class="arg">$color</span>, <span class="arg">$amount</span>)
+  .details
+    %p
+      Scales <code>$color</code>'s saturation value by <code>$amount</code>.
+      <code>$amount</code> can be negative.

lib/compass/sass_extensions/functions.rb

@@ -4,7 +4,7 @@ end
 %w(
   selectors enumerate urls display
   inline_image image_size gradient_support
-  font_files constants lists
+  font_files constants lists colors
 ).each do |func|
   require "compass/sass_extensions/functions/#{func}"
 end
@@ -20,6 +20,7 @@ module Sass::Script::Functions
   include Compass::SassExtensions::Functions::FontFiles
   include Compass::SassExtensions::Functions::Constants
   include Compass::SassExtensions::Functions::Lists
+  include Compass::SassExtensions::Functions::Colors
 end
 
 # Wierd that this has to be re-included to pick up sub-modules. Ruby bug?

lib/compass/sass_extensions/functions/colors.rb

@@ -0,0 +1,44 @@
+module Compass::SassExtensions::Functions::Colors
+
+  # a genericized version of lighten/darken so that negative values can be used.
+  def adjust_lightness(color, amount)
+    assert_type color, :Color
+    assert_type amount, :Number
+    color.with(:lightness => Sass::Util.restrict(color.lightness + amount.value, 0..100))
+  end
+
+  # Scales a color's lightness by some percentage.
+  # If the amount is negative, the color is scaled darker, if positive, it is scaled lighter.
+  # This will never return a pure light or dark color unless the amount is 100%.
+  def scale_lightness(color, amount)
+    assert_type color, :Color
+    assert_type amount, :Number
+    color.with(:lightness => scale_color_value(color.lightness, amount.value))
+  end
+
+  # a genericized version of saturation/desaturate so that negative values can be used.
+  def adjust_saturation(color, amount)
+    assert_type color, :Color
+    assert_type amount, :Number
+    color.with(:saturation => Sass::Util.restrict(color.saturation + amount.value, 0..100))
+  end
+
+  # Scales a color's saturation by some percentage.
+  # If the amount is negative, the color is desaturated, if positive, it is saturated.
+  # This will never return a pure saturated or desaturated color unless the amount is 100%.
+  def scale_saturation(color, amount)
+    assert_type color, :Color
+    assert_type amount, :Number
+    color.with(:saturation => scale_color_value(color.saturation, amount.value))
+  end
+
+  private
+  def scale_color_value(value, amount)
+    if amount > 0
+      value += (100 - value) * (amount / 100.0)
+    elsif amount < 0
+      value += value * amount / 100.0
+    end
+    value
+  end
+end

test/sass_extensions_test.rb

@@ -37,6 +37,28 @@ class SassExtensionsTest < Test::Unit::TestCase
     assert_equal "h4, h5, h6", evaluate("headers(4,6)")
   end
 
+  def test_scale_lightness
+    assert_equal "75%", evaluate("lightness(scale-lightness(hsl(50deg, 50%, 50%), 50%))")
+    assert_equal "25%", evaluate("lightness(scale-lightness(hsl(50deg, 50%, 50%), -50%))")
+  end
+
+  def test_adjust_lightness
+    assert_equal "75%", evaluate("lightness(adjust-lightness(hsl(50deg, 50%, 50%), 25%))")
+    assert_equal "25%", evaluate("lightness(adjust-lightness(hsl(50deg, 50%, 50%), -25%))")
+    assert_equal "100%", evaluate("lightness(adjust-lightness(hsl(50deg, 50%, 50%), 500%))")
+    assert_equal "0%", evaluate("lightness(adjust-lightness(hsl(50deg, 50%, 50%), -500%))")
+  end
+
+  def test_scale_saturation
+    assert_equal "75%", evaluate("saturation(scale-saturation(hsl(50deg, 50%, 50%), 50%))")
+    assert_equal "25%", evaluate("saturation(scale-saturation(hsl(50deg, 50%, 50%), -50%))")
+  end
+
+  def test_adjust_saturation
+    assert_equal "75%", evaluate("saturation(adjust-saturation(hsl(50deg, 50%, 50%), 25%))")
+    assert_equal "25%", evaluate("saturation(adjust-saturation(hsl(50deg, 50%, 50%), -25%))")
+  end
+
 protected
   def evaluate(value)
     Sass::Script::Parser.parse(value, 0, 0).perform(Sass::Environment.new).to_s