add new platform_abstraction

add support of loading ttf file

source/detail/platform_abstraction.hpp

@@ -0,0 +1,43 @@
+/*
+ *	Platform Abstraction
+ *	Nana C++ Library(http://www.nanapro.org)
+ *	Copyright(C) 2017 Jinhao(cnjinhao@hotmail.com)
+ *
+ *	Distributed under the Boost Software License, Version 1.0.
+ *	(See accompanying file LICENSE_1_0.txt or copy at
+ *	http://www.boost.org/LICENSE_1_0.txt)
+ *
+ *	@file: nana/detail/platform_spec.hpp
+ *
+ *	The platform_abstraction provides some functions and types for the abstract
+ *	system platform.
+ */
+#ifndef NANA_DETAIL_PLATFORM_ABSTRACTION_HEADER_INCLUDED
+#define NANA_DETAIL_PLATFORM_ABSTRACTION_HEADER_INCLUDED
+
+#include "platform_abstraction_types.hpp"
+#include <memory>
+#include <nana/filesystem/filesystem.hpp>
+
+namespace nana
+{
+
+
+	class platform_abstraction
+	{
+	public:
+		using font = font_interface;
+
+		using path_type = ::std::experimental::filesystem::path;
+
+		static void initialize();
+		/// Shutdown before destruction of platform_spec 
+		static void shutdown();
+		static ::std::shared_ptr<font> default_font(const ::std::shared_ptr<font>&);
+		static ::std::shared_ptr<font> make_font(const ::std::string& font_family, double size_pt, const font::font_style& fs);
+		static ::std::shared_ptr<font> make_font_from_ttf(const path_type& ttf, double size_pt, const font::font_style& fs);
+		static void font_resource(bool try_add, const path_type& ttf);
+	};
+}
+
+#endif