Pushing objects between C++ and Lua?

[epicasian]

I recently added Lua to my engine and am wondering how to push an object created in C++ to Lua so I can modify the values with a script. I'm using toLua++, if that matters.


Also, would I have to wrap SFML to Lua to do something like:

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RenderWindow.Draw(SomeSprite);

Thanks in advance.

[N64vSNES]

I've not used tolua to be honest but I've been looking into it recently and as far as I know you can't really throw a C++ object at lua but what I recommend you do is

Supposing we have a player class and you want to wrap it to lua then I suggest you have a singelton class as a Game-Manager so you can have objects in it such as a map object, a player object etc

And then you use those objects to get the values from lua

Heres a little example ( sorry its not in tolua, I'm still to look into that further )

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int SetPlayerHP(lua_State *l) {

// Get the first argument passed from lua
int amount = lua_tointeger(l,1);

// Set the players HP to the value we retrived from lua
GameManager::GetInstance()->Player.SetHP(amount);

return 0;
}

// This should be called in when the game is initialized
void ExportFunctions() {
// Register the function
lua_register( LuaState, "SetPlayerHP", SetPlayerHP );
}

Now you can call SetPlayerHP(value) from lua and it will set the value.

The might be a way to pass a actual object to lua since your using tolua but this method seems fine to me.

EDIT:
Oh and one last thing, for the project I'm working on I have to make sure that you can do

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SomeNPC = AddNPC()

And the way I handle that is having the lua function return a integer so then you can say stuff like

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RemoveNPC(SomeNPC)

The NPC subsystem actully has an array of NPCs and it returns the index of that array.
If that helps any

[epicasian]

Thanks for telling me, and I definitely recommend using toLua, it's hella easy.

--edit-- I've got a debug singleton, but I don't know how I would create it in Lua. I've tried:

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Dbg = GE.Debug:GetInstance()
Dbg:Init()
Dbg:Print("A Message")

My GetInstance() returns a static Debug instance, my Init() opens a file and my Print() prints to the file

[N64vSNES]

Thanks for telling me, and I definitely recommend using toLua, it's hella easy.

--edit-- I've got a debug singleton, but I don't know how I would create it in Lua. I've tried:

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Dbg = GE.Debug:GetInstance()
Dbg:Init()
Dbg:Print("A Message")

My GetInstance() returns a static Debug instance, my Init() opens a file and my Print() prints to the file

Ok from what I've heard tolua and tolua++ generates a .PKG file that you open in a lua state, so looking at a few tutorials should explain this pretty easily.

Wish I could help more but I really haven't used tolua enugh...:/

[Falco Girgis]

Thanks for telling me, and I definitely recommend using toLua, it's hella easy.

--edit-- I've got a debug singleton, but I don't know how I would create it in Lua. I've tried:

Code: Select all

Dbg = GE.Debug:GetInstance()
Dbg:Init()
Dbg:Print("A Message")

My GetInstance() returns a static Debug instance, my Init() opens a file and my Print() prints to the file

And what is wrong with this approach? What is the Lua error? That's exactly how we handle quite a bit of stuff in the ES engine.

With toLua++, passing data to and from C++ is literally as easy as returning a pointer or a reference...

And to answer your answer question...do you really want to "create" something as vital as a debug class in Lua? I think what you mean to say is "access." Your subsystems/major functionality should exist in your engine and simply be "utilized" through Lua.