worked out a simple way to call a lua function as a method based on the overridable_function_members.cpp

example

src/scripting/src/script_system.cpp

@@ -4,16 +4,33 @@
 #include "pw/system/input.hpp"
 #include "pw/system/display.hpp"
 
+#include "pw/core/debug.hpp"
+
 // hijacking
 //#include "pw/visual/pipeline.hpp"
 
 namespace pw {
 
+struct window_lua : public window {
+	// overridable function
+	sol::function lua_update;
+
+	window_lua(sol::this_state L)
+	// default is an empty callback
+		: lua_update(sol::make_reference<sol::function>(L.lua_state(), [](){}))
+	{
+		// set this internal callback of the window to the lua callback
+		_on_update = [this](window&){this->lua_update();};
+	}
+};
+
+
 void script_system::load(sol::table &ns)
 {
-	ns.new_usertype<window>("window",
+	ns.new_usertype<window_lua>("window",
+								sol::constructors<window_lua(sol::this_state)>(),
+								"on_update",&window_lua::lua_update,
 								"update",&window::update,
-                            "set_on_update",&window::set_on_update,
 								"title",sol::writeonly_property(&window::set_title),
 								"size",sol::property(&window::size,&window::set_size),
 								"position",sol::property(&window::position,&window::set_position),

src/scripts/demos/simple_000.lua

@@ -70,6 +70,11 @@ local w = pw.window.new()
 -- set title
 w.title = "pixwerx 0.1"
 
+-- setup a lua callback function
+w.on_update = function(self)
+    print("test on update",w.position.x,w.position.y)
+end
+
 -- set size
 w.size = pw.size.new(800,600)
 -- move window