🔒 Locked

Lua function as C++ parameter?

Started by Tenac Jul 12, 2008 at 1:17 AM 5 replies 2.7k views

Original Post

Jul 12, 2008 at 1:17 AM

I'm using lua and luabind to link my C++ classes/methods to lua mainly for GUI creation similar to world of warcraft's but I ran into one think I can't figure out, how can I have a lua function as a parameter in a C++ method. An example in lua would be: local Frame = CreateFrame("Frame", nil); Frame:SetScript("OnMouseDown", function() print("print me!"); end); What would SetScript look like in C++? Currently I have it as SetScript(string foo1, const char* foo2) and I put the second parameter in quotes in lua so I could do luaL_dostring but it's time for me to fix this. Would anyone know what I could do to make this possible?

Tenac

Author

Tenac

Jul 15, 2008 at 12:19 AM

Is this even possible or if not, is there some sort of alternative? Did WoW modify lua to be able to do this?

hh10k

Jul 15, 2008 at 12:32 AM

Lua's normal C API lets you take a function (or anything else) as a parameter, but I'm not familiar with luabind. Sorry I can't help more :)

ddn3

124

ddn3

Jul 15, 2008 at 12:43 AM

A simple way would be have some intermediary in Lua to hold these functions in a table, which u can index with a simply interger key from C++ script. So internally to C++ the lua function is a handle into this table. And when it comes to disaptch the function u go through a catch all Lua function which interns accesses the functor table to dispatch the call. Not most efficent since ur doing somewhat more work but its ezy.

-ddn

rudeness

Jul 16, 2008 at 6:36 PM

Hello.

luaL_ref does what ddn3 suggests.

Recently, I needed to attach arbitrary Lua data to Shape objects for collision response purposes. Here's some code:

(Table love.refs holds the references.)

// First param is the object in question.// Second param is arbitrary data.int _CircleShape_setData(lua_State * L){	if(lua_gettop(L) != 2) return luaL_error(L, "Incorrect number of parameters.");	pCircleShape p = mod_to_circleshape(L, 1);	lua_getglobal(L, "love");	lua_getfield(L, -1, "refs");	lua_pushvalue(L, -3); // Copies second param to the top.	int ref = luaL_ref(L, -2);	p->setData(ref);	return 0;}int _CircleShape_getData(lua_State * L){	if(lua_gettop(L) != 1) return luaL_error(L, "Incorrect number of parameters.");	pCircleShape p = mod_to_circleshape(L, 1);	int ref = p->getData();	lua_getglobal(L, "love");	lua_getfield(L, -1, "refs");	lua_rawgeti(L, -1, ref);	return 1;}

This way you can "store" Lua data (including functions) in C++ using a single int.

bobofjoe

Jul 16, 2008 at 10:52 PM

Using luabind, you can accept functions to your C++ functions in the form of luabind::object.

In order to invoke that function, you will have to call luabind::call_function( functionObject, args ... );
or
functionObject( args ... );

Example!

//C++luabind::object functionObject;void setObject(luabind::object func){	functionObject = func;}void invoke(){	if (luabind::type(functionObject) == LUA_TFUNCTION)	{		luabind::call_function<void>(functionObject);		//This syntax also works:		//functionObject();	} else {		//You did it wrong.		throw std::runtime_exception("Lua Object not a function.");	}}void bindToLua(lua_State * state){	luabind::open(state);	luabind::module(state)	[		luabind::def("setObject", setObject),		luabind::def("invoke", invoke)	];}//Lua (Assuming you have bound the correct stuff correctly, of course)function Foo()	print("I see what you did thar");endsetObject(Foo);invoke();

This should print "I see what you did thar" to the console. This is pretty much as type safe as it is going to get, since lua dosn't really have a strict typing system.

Note that you will have to

#include <luabind/object.hpp>

to get this to work, though.

Tenac

Author

Tenac

Aug 13, 2008 at 8:13 PM

bobofjoe, your the greatest, that worked perfectly how I wanted it to!

Thanks everyone for the help and I gave all of you good ratings.

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.