Re: object handling

["Brett Bibby" <research@...>]

Kevin,
That's very helpful, thanks.  If I call a functin that deletes an object
in my engine, can I then delete the table (e.g.A123) by setting it to
nil?
Thanks again,
Brett

----- Original Message ----- 
From: "Kevin Baca" <lualist@aidiastudios.com>
To: "'Lua list'" <lua@bazar2.conectiva.com.br>
Sent: Wednesday, October 15, 2003 10:09 AM
Subject: RE: object handling


> To pass the table A123 to a lua function from C:
>
> //Retrieve the lua function
> lua_pushstring( L, "funcname" )
> lua_gettable( L, LUA_GLOBALSINDEX );
>
> //Retrieve A123 (assuming it is a global)
> lua_pushstring( L, "A123" )
> lua_gettable( L, LUA_GLOBALSINDEX )
>
> lua_call( L, 1, 0 ) //call funcname() with 1 arg and 0 return vals
>
> Some other things to think about:
>
> You could have a lua function create the lua table and the C object
> simultaneously, then store a reference (userdata) to the C object in
the
> lua table.
>
> Conversely, create the lua table and the C object simultaneously from
C
> and store a reference to the lua table in the C object (perhaps using
> the lua_ref() macro).
>
> Or you can mix and match as you desire.
>
> Either way, once you have a way to create objects you might want to
> think about defining all object variables (C-side and lua-side) in lua
> because lua provides such a nice syntax for that sort of thing.
>
> Example:
>
> -- This creates a new tank object that contains a reference
> -- to a C object (as a userdata)
>
> function Tank( tankDef )
>     local tank =
>     {
>         ammo = tankDef.ammo,
>         health = tankDef.health
>     }
>
>     -- Create the C object (a userdata) and store a ref to
>     -- it in tank.__cobj__
>     tank.__cobj__ = C_tankCreate( tankDef.actorData )
>
>     return tank
> end
>
> -- The following will call Tank() and tank0 will
> -- refer to the new tank
>
> tank0 = Tank
> {
>     ammo = 10,
>     health = 100,
>     actorData =
>     {
>         -- Internal C data
>         followTerrain = true,
>         collideable = true,
>     }
> }
>
> This way you can define lua-side data and C-side data in in the same
lua
> config table.
>
> Hope that makes sense.
>
> -Kevin
>
> > Newbie question....
> >
> > We're trying to come up with an efficient way to handle our
> > game objects from lua.  For a given game object, we define a
> > complete schema that includes the engine data and the game
> > extensions to that data.  So for example, an Actor schema
> > will have some core internal use variables and some
> > additional game specific variables (e.g. tank might have
> > armor, player might have health, etc.)  Currently, we stuff
> > the engine's internal variables into a C struct and the
> > additional variables into a lua table, then use lua bindings
> > to call engine functions that operate on the internal data
> > and use lua directly to manipulate the lua tables. So far so good.
> >
> > At authoring time all of this is transparent to the designer.
> >  They simply create instances of actors and add new variables
> > to them as they need them.  When they export the game, we
> > split the data and generate a guid for each engine object and
> > embed that in the engine data and then create a lua table
> > with the same name as the guid that also contains elements to
> > hold the additional variables.
> >
> > My questions are:
> >
> > 1.  Is this a lame way to do this?  What are the other ways?
> > (either implicitly or explicitly) 2.  If I have a guid of
> > A123 (stored as a 4 byte int, not char) and I create a lua
> > table as A123 = {}, when I call from the engine into lua,
> > what do I need to pass lua (or configure before calling) so
> > that a lua funciton can receive the correct table to operate
> > on?  I tried several experiments passing in the A123 as a
> > number and a string and it doesn't work.  Do I need to pass
> > the table itself?  How do I do that?
> >
> > Thanks for the help.
> > Brett
> >