RE: Lua Use in Visual Basic

["Virgil Smith" <Virgil@...>]

<warning mixing multiple replies in one message>

> I don't remember all the differences, but I thought the
> major one was order that arguments are pushed on the
> stack.  If that's the real one that matters, then you
> should be ok, as the callbacks only have 1 param.  I don't
> remember offhand how the return value is handled, and that
> may be the kicker.

No, as I stated before, "__stdcall and __cdecl differ in stack cleanup
strategy".  In other words they differ in whether the called function pops
the arguments off the stack or if the calling function pops the arguments
off the stack.  For more information just look up __cdecl and __stdcall in
the MSDN help.


> Well, yes of course, but I was a bit concerned because
> it sounds like i have to write a wrapper DLL in C
> because of the calling conventions.
> Even if I'm in an ActiveX DLL, I can only define __stdcall
> functions...so I can't use any VB function as a Lua callback.
> Jim just suggested this is true while I was writing this.

Ah, now we've come all the way back around.
You could go reread my original reply at this point.
The easiest way to reflect a "callback" to VB is with an OLE/ActiveX event.
Now, you would probably like to avoid having to make a separate C function
and/or ActiveX event per function that your "wrapper DLL" registers with
Lua.
To pull that trick off, I recommend the use of lua_pushcclosure specifying
an upvalue.  That way when your 1 C function gets called by Lua, it can
extract the upvalue and supply that as a parameter of the OLE Event.  That
way your VB code can do its dispatching based on that value.

Um, good luck, I've done all I can.



-----Original Message-----
From: lua-bounces@bazar2.conectiva.com.br
[mailto:lua-bounces@bazar2.conectiva.com.br]On Behalf Of Isaac Raway
Sent: Friday, January 30, 2004 5:09 PM
To: Lua list
Subject: Re: Lua Use in Visual Basic


Virgil Smith wrote:

>Just build your own DLL its just too easy for anyone to have bothered
>maintaining a public one :-)
>
>IIRC to make a C/VB callable DLL you've just got to add a def file to the
>DLL project rather than just using __declspec(dllexport).
>
>I'll send you a Lua5 def file directly (off list).
>
>If that does not work, then you should just be able to mark all of the lua
>api functions as "__declspec(dllexport) __stdcall" (or pick your favorite
>macro like WINAPI).  The LUA_API macro should come in handy to keep that
>from being tedious.
>
>BTW: OLE Events are easy to manage using VC5 or later, just be sure to make
>an ActiveX DLL or OCX project rather than a "plain" win32 DLL project.
>
>
>
Well, yes of course, but I was a bit concerned because it sounds like i
have to write a wrapper DLL in C because of the calling conventions.
Even if I'm in an ActiveX DLL, I can only define __stdcall
functions...so I can't use any VB function as a Lua callback. Jim just
suggested this is true while I was writing this.

>-----Original Message-----
>From: lua-bounces@bazar2.conectiva.com.br
>[mailto:lua-bounces@bazar2.conectiva.com.br]On Behalf Of Isaac Raway
>Sent: Friday, January 30, 2004 4:25 PM
>To: Lua list
>Subject: Re: Lua Use in Visual Basic
>
>
>Virgil Smith wrote:
>
>
>
>>>On Thursday 29 January 2004 17:31, Virgil Smith wrote:
>>>
>>>
>>>
>>>
>>>>As Jamie said calling into Lua should be very simple through a DLL.
>>>>Probably your difficult bits will be having Lua call you when scripts
>>>>
>>>>
>>>>
>>>>
>>call
>>
>>
>>
>>
>>>>functions you've registered cause metamethod invocations etc.  Without
>>>>putting a lot of thought into it I'd expect that you're going to want to
>>>>make an OLE DLL or OCX and trigger OLE events to handle "callbacks from
>>>>Lua".
>>>>
>>>>
>>>>
>>>>
>>>The VB AddressOf operator (added in VB5 IIRC) allows you to take the
>>>address of a function (again as a Long, I think). It works fine with
>>>Windows API callbacks, so it should work with Lua as well.
>>>
>>>-- Jamie Webb
>>>
>>>
>>>
>>>
>>Nope, that will blow up your stack (unless you change the Lua sources).
>>
>>VB uses the __stdcall calling convention.
>>Win32 Callback functions (designated by the macro "CALLBACK" in the VC
>>supplied headers), use the __stdcall calling convention as well.  The Lua
>>sources use __cdecl (that's the default/standard C calling convention).
>>__stdcall and __cdecl differ in stack cleanup strategy so mixing them is a
>>Bad Idea (tm).
>>
>>You could of course change the Lua sources in the DLL used by VB so that
>>they use the __stdcall calling convention, but be sure to be thurough
about
>>it if you do.
>>
>>Also, handling the callbacks directly like this will give you lots of
>>headaches while debugging under VB (at least version 6 or earlier, I have
>>
>>
>no
>
>
>>experience with the later ones).
>>
>>
>>
>>
>>
>That's sort of bad then. I was hoping I could write a DLL to talk to Lua
>without having to dive into my own C DLL...it just adds another layer to
>the system. I'd change the call methods, but then I'd have to do that
>for every release of Lua. Doesn't sound like too much fun.
>
>Also, if what you say about __cdecl and __stdcall is true, then how can
>I call the DLL at all in VB? It must be figuring out what convention the
>DLL is using I suppose, which the Lua DLL won't do when it calls the
>pointer I give it from AddressOf.
>
>Dang. I don't know anything about firing events in a C DLL...looks like
>I have some reading up for me?
>
>
>Oh, also, I can't seem to get a Lua DLL. I've found plenty of Windows
>distros, but they are all EXEs without external DLLs. Any thoughts?
>
>~ Isaac
>
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