Using Lua in your application

Renato Tegon Forti

4.58/5 (18 votes)

May 5, 2005

2 min read

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Way to integrate Lua in your application.

*Lua script (below) to customize preferences and content of UI (above).

Introduction

This article shows a way to integrate Lua in your application.

What is Lua?

Lua is an extension programming language designed to support general procedural programming with data description facilities. It also offers good support for object-oriented programming, functional programming, and data-driven programming. Lua is intended to be used as a powerful, light-weight configuration language for any program that needs one. Lua is implemented as a library, written in clean C (that is, a common subset of ANSI C and C++).

Sample of Lua Syntax (FOR loop):

for i=1,10 do
    -- the first program in every language
    io.write("Hello world, from ",_VERSION,"!\n")
end

For full description see: About.

Background

This sample is a WTL application (simple HTML help systems), that integrates Lua scripts to customize preferences and content.

It defines the Lua function:

-- # MessageBox
--------------------------------------------------------
-- int MessageBox(
-- string msg, |= Message to display
-- string capition |= Capition of Box
-- );
-- Return Value:
-- if 1 the user click in OK or user close the box


-- # ShowContentPainel
-----------------------------------------------------------------
-- void ShowContentPainel(
-- bool bShow |= If true, the painel start opened, if false not.
-- );

-- # SetWindowStartSize
-----------------------------------------------------------------
-- void SetWindowStartSize(
-- number w, |= Start W size of window
-- number h, |= Start H size of window
-- );
-- Remarks:
-- if this function is not called, the default size is 800 x 600

-- # SetMinWindowSize
-----------------------------------------------------------------
-- void SetMinWindowSize(
-- number w, |= Minimum W size of window
-- number h, |= Minimum H size of window
-- );

-- # SetTitle
-----------------------------------------------------------------
-- void SetTitle(
-- string title |= Text that be title of window.
-- );

-- # Navigate
-----------------------------------------------------------------
-- void Navigate(
-- string url |= Url
-- );

-- # InsertItemInPainel
-----------------------------------------------------------------
-- void InsertItemInPainel(
-- string title, |= Text displayed in tree
-- string url, |= Url
-- number icon, |= Icon of item, the possible values 
                           ---are: 0 = BOOK, 1 = FILE, 2 = NETFILE
-- number id, |= Id of item, this has to be unique and start in 1
-- number idp |= Parent item, this is a ID of a item that is 
                                ---the parent or '0' for root item.
-- );
-- sample:
-- ICON BOOK / ID 1 / In ROOT
-- InsertItemInPainel("Trinity Systems", 
            "http://www.novaamerica.net/trinitysystems/", 0, 1, 0); 
-- ICON NETFILE / ID 2 / In ID1 (Trinity Systems)
-- InsertItemInPainel("Orion", 
       "http://www.novaamerica.net/trinitysystems/Orion", 2, 2, 1); 

-- # ExpandItemInPainel
------------------------------------------------------------------
-- void ExpandItemInPainel(
-- string id |= Id of item
-- );
-- Remarks:
-- This function need to be called after InsertItemInPainel's

...and now I'll show you how to create these functions in Lua/C++.

Code

The first thing to do is to build the DLL that contains Lua. (download Lua DLL demo project)

Link this in your project:

//

// For sample:

//

//---------------------------------------------

// Library Linkage

//---------------------------------------------

//-

#if defined (_DEBUG)
#pragma comment( lib, "lua.lib" ) // Lua Support

#else
#pragma comment( lib, "lua.lib" ) // Lua Support

#endif
//-

Remember: To change your Project Property -> linker -> general -> additional library directory: lua lib directory.

Add Lua include files:
```
extern "C" 
{
#include "lua.h"

}
```
Remember: To change your Project Property -> C/C++ -> general -> additional include directories: lua include directory.

Notice that all the files in lua lib need to stay with "c" extension, because Lua was written to be ANSI C compliant.

Now we need to start Lua VM as follows:

LRESULT OnCreate(UINT 
/*uMsg*/, WPARAM /*wParam*/, LPARAM /*lParam*/, BOOL& 
/*bHandled*/)
{
//...

// Lua

//

lua_State *luaVM = lua_open(); /* 
Open Lua */
//

luaopen_base(luaVM );     /* opens the 
basic library */
luaopen_table(luaVM );    /* opens the table 
library */
luaopen_io(luaVM );       /* opens 
the I/O library */
luaopen_string(luaVM );   /* opens the string 
lib. */
luaopen_math(luaVM );     /* opens the math lib. 
*/
if (NULL == 
luaVM)
{
         
MessageBox("Error Initializing lua\n");
}
//...

// Do things with lua 

code.
// see below

//...

lua_close(luaVM); /* Close Lua */
//

// 

End
//...

}

Now we make a glue function of Lua and C/C++.

The Lua API function to do this is:

lua_register(s, n, g)

where

s: is the lua_State to register the function.
n: is the name of the function exposed to Lua.
g: the C/C++ glue function.

See the sample:

//...

// Do things with 

lua code.
lua_register( luaVM, "SetHome", l_SetHome );
//...

// 

-------------------------------------------
// 

#Lua Functions
// 

------------------------------------------
//

static 
int l_SetTitle( lua_State* 
luaVM)
{
         const char* 
title = luaL_checkstring(luaVM, 
1);
         
theMainFrame->SetWindowText(title);
         
return 0;
}

Now we need the load and execute Lua scripts:
```
//...

// Do things with lua 

code.
lua_register( luaVM, "SetHome", l_SetHome );
//more glue 

functions
lua_dofile(luaVM, "hrconf.lua");
//...
```
The Lua API function to do this is:
```
lua_dofile(s, p)
```
where
- s: is the lua_State to register the function.
- p: path for Lua script file.
See the demo script.

For a complete understanding of the Lua API, see: Lua 5.0 Reference Manual.

Points of interest

Lua is a free software.
Download Lua: Download.
Manual: Reference manual for Lua 5.0.
References: Lua.

History

29^th April 2005: First release.