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Luabind to access classes.

Started by JesseWerner Apr 1, 2011 at 5:34 PM 2 replies 2.7k views

Original Post

Apr 1, 2011 at 5:34 PM

Hi, I want to have a class representing a game object and I want to be able to have access to it from both lua and c++.

Right now I parse my scene file and call this code to create objects:

luabind::object myObject = globals(L)[name]["__init"]();
GameObject *gameObject = luabind::object_cast ( myObject );

This does call the luabind object and return the game object. I have verified this by changing the "name" value in my lua constructor and printing it out in the GameObject update function on the c++ side. The problem is I dont know how to continue to call lua functions on this object. Does anyone have any ideas?

EDIT: So since the lua __init function called above can change members on the game object, I have no idea why this wouldnt work:

luabind::object myObject = globals(L)[name]["__init"]();
myObject["update"]();

Calling update makes it crash. And if i call update in the constructor of the derived lua class, it calls the c++ GameObject update D=

JesseWerner

Apr 2, 2011 at 9:57 AM

After searching exhaustively for the answer to this, I have found no results. I have decided to ditch luabind and create my own structure for binding classes on top of lua.
If anyone has any suggestions or resources let me know =)

diablos_blade

Apr 2, 2011 at 10:12 AM

After searching exhaustively for the answer to this, I have found no results. I have decided to ditch luabind and create my own structure for binding classes on top of lua.
If anyone has any suggestions or resources let me know =)

__init requires a self parameter and returns nothing.
Update probably requires a self parameter too.

If you really want to create objects this way, I suggest something like this:

// Will call the global function called "name", which, from lua-side, acts as you'd expect a "obj = new Object( )" to work
 luabind::object myObject = luabind::call_function<luabind::object>( name )[luabind::adopt(luabind::_return);
 myObject["update"]( );

The function calls might not be exactly right, but should give you an idea.

However, I've had a few crashes lately with luabind not keeping references to objects alive which were created lua-side but stored C++-side. Although this was also using lua-side specialisation of classes, so your case may not be affected.

JesseWerner

Apr 3, 2011 at 8:37 AM

Is it possible to pass a self parameter to lua from the c++ side?

Also so you must make a global function for each of your lua classes?

Edit: Your post convinced me to play around with is some more. I managed to get it to work with aggregation but I cant get inheritance to work.

In lua I have:


 class 'Derived' 
 
 function Derived:__init(userdata)
 self.gameObject = userdata
 userdata:setName("name set from lua")
 self.gameObject:printName()
 end

That works just fine. I can access my game object through the lua "gameObject" field. But does anyone know why this wouldnt work:

class 'Derived' (GameObject)
 
 function Derived:__init()
 self:setName("name set from lua")
 self:printName()
 end

I read somewhere that you can use super to call the base class constructor. That throws errors. I tried directly calling __init and that throws errors as well.

EDIT: I was wrong, it doesnt work as I previously thought. I can edit the data in the constructor but I cant call any other functions from the lua object even though i set "self.gameObject = userdata". I must be missing something...

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