Diff of OpenGL/Headless

• The added line is THIS COLOR.
• The deleted line is THIS COLOR.
• Go to OpenGL/Headless.

- OpenGL ヘッドレスモード
--  http://d.hatena.ne.jp/yoya/20140224/opengl

- OpenGLでオフスクリーンレンダリング
--  http://qiita.com/7shi/items/b02f2e45b49c0314fd12