Changed how userdata is handled

luprex/core/cpp/gui.hpp

@@ -2,6 +2,7 @@
 #define GUI_HPP
 
 #include <string>
+#include <map>
 #include <vector>
 #include "luastack.hpp"
 
@@ -34,7 +35,17 @@ public:
     void clear() { elts_.clear(); }
     bool has_action(const std::string &action) const;
     void menu_item(const std::string &action, const std::string &label);
+
+    // Put a pointer to a gui into the lua registry.
+    //
+    // All lua commands that manipulate the GUI implicitly
+    // operate on this global gui pointer.
+    //
+    static void store_global_pointer(lua_State *L, Gui *g);
+    static Gui *fetch_global_pointer(lua_State *L);
 };
 
+using GuiResult = std::map<std::string, std::string>;
+
 #endif // GUI_HPP