Add Ability to Use Color Class

Add the ability to set fill_color, stroke_color, etc. with something
other than a string. This class should have a method color_str that
returns a hex string representing the color.

lib/prawn/graphics/color.rb

@@ -74,6 +74,7 @@ def rgb2hex(rgb)
       #  => [255, 120, 8]
       #
       def hex2rgb(hex)
+        hex = hex.respond_to?(:to_str) ? hex.to_str : hex.color_str
         r,g,b = hex[0..1], hex[2..3], hex[4..5]
         [r,g,b].map { |e| e.to_i(16) }
       end
@@ -93,9 +94,11 @@ def process_color(*color)
 
       def color_type(color)
         case color
-        when String
+        when -> (color) { color.respond_to?(:to_str) }
           :RGB
-        when Array
+        when -> (color) { color.respond_to?(:color_str) }
+          :RGB
+        when -> (color) { color.respond_to?(:to_ary) }
           case color.length
           when 3
             :RGB

spec/graphics_spec.rb

@@ -243,13 +243,31 @@
     colors.stroke_color.should == [1.0, 0.8, 0.8]
   end
 
+  it "should accept stroke colors from objects that support color_str" do
+    color = mock('color')
+    color.expects(:color_str).returns("ffcccc")
+    @pdf.stroke_color color #"ffcccc"
+    colors = PDF::Inspector::Graphics::Color.analyze(@pdf.render)
+    # 100% red, 80% green, 80% blue
+    colors.stroke_color.should == [1.0, 0.8, 0.8]
+  end
+
   it "should set fill colors" do
     @pdf.fill_color "ccff00"
     colors = PDF::Inspector::Graphics::Color.analyze(@pdf.render)
     # 80% red, 100% green, 0% blue
     colors.fill_color.should == [0.8,1.0,0]
   end
 
+  it "should accept fill colors from objects that support color_str" do
+    color = mock('color')
+    color.expects(:color_str).returns("ccffcc")
+    @pdf.fill_color color #"ffcccc"
+    colors = PDF::Inspector::Graphics::Color.analyze(@pdf.render)
+    # 100% red, 80% green, 80% blue
+    colors.fill_color.should == [0.8, 1.0, 0.8]
+  end
+
   it "should reset the colors on each new page if they have been defined" do
     @pdf.fill_color "ccff00"
     #colors = PDF::Inspector::Graphics::Color.analyze(@pdf.render)