Opacity improvements

Adds opacity attribute reader for `Ruby2D::Color` and
`Ruby2D::Color::Set`. Adds `opacity/=` method to renderable objects, a
shortcut for `obj.color.opacity/=`.

1 files changed, 11 insertions, 0 deletions

diff --git a/test/color_spec.rb b/test/color_spec.rb
index 95033a9..0fb65c8 100644
--- a/test/color_spec.rb
+++ b/test/color_spec.rb
@@ -32,4 +32,15 @@ RSpec.describe Ruby2D::Color do
     end
   end
   
+  describe '#opacity' do
+    it 'sets and returns the opacity' do
+      s1 = Square.new
+      s1.opacity = 0.5
+      s2 = Square.new(0, 0, 0, ['red', 'green', 'blue', 'yellow'])
+      s2.opacity = 0.7
+      expect(s1.opacity).to eq 0.5
+      expect(s2.opacity).to eq 0.7
+    end
+  end
+  
 end