fix bug that transparent widget may not be updated in event handler(#431)

include/nana/gui/detail/bedrock.hpp

@@ -1,7 +1,7 @@
 /**
  *	A Bedrock Implementation
  *	Nana C++ Library(http://www.nanapro.org)
- *	Copyright(C) 2003-2018 Jinhao(cnjinhao@hotmail.com)
+ *	Copyright(C) 2003-2019 Jinhao(cnjinhao@hotmail.com)
  *
  *	Distributed under the Boost Software License, Version 1.0.
  *	(See accompanying file LICENSE_1_0.txt or copy at
@@ -43,6 +43,20 @@ namespace detail
 
 		class flag_guard;
 
+		/// RAII class for window message processing
+		class root_guard
+		{
+		public:
+			/// Enables lazy_update
+			root_guard(bedrock& brock, basic_window* root_wd);
+
+			/// Disables lazy-update and clears update requesters queue.
+			~root_guard();
+		private:
+			bedrock& brock_;
+			basic_window* const root_wd_;
+		};
+
 		~bedrock();
 		void pump_event(window, bool is_modal);
 		void flush_surface(core_window_t*, bool forced, const rectangle* update_area = nullptr);

include/nana/gui/detail/window_manager.hpp

@@ -117,6 +117,7 @@ namespace detail
 		void map(core_window_t*, bool forced, const rectangle* update_area = nullptr);
 
 		bool update(core_window_t*, bool redraw, bool force, const rectangle* update_area = nullptr);
+		void update_requesters(core_window_t* root_wd);
 		void refresh_tree(core_window_t*);
 
 		void do_lazy_refresh(core_window_t*, bool force_copy_to_screen, bool refresh_tree = false);