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<html>
<head>
<meta http-equiv="Content-Language" content="en-us">
<title>Lua Binding</title>
<link rel="stylesheet" type="text/css" href="../style.css">
</head>
<body>
<h1>Lua Binding</h1>
<h3><a name="Overview">Overview</a></h3>
<p>CDLua was developed to make all functionalities of the CD library available to Lua programmers. To use the CDLua
bindings, your executable must be linked with the CDLua library, and you must call the initialization function <strong>
<font face="Courier New">cdlua_open</font></strong> declared in the header file <strong><font face="Courier New">cdlua</font><font size="2" face="Courier New">.</font><font face="Courier New">h</font></strong>,
as seen in the example below:</p>
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<p align="center">in Lua5</th>
</tr>
<tr>
<td>
<pre>#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
<b><font color="#FF0000">#include <cdlua.h></font></b></pre>
<pre>void main(void)
{
lua_State *L = lua_open();
luaopen_string(L);
luaopen_math(L);
luaopen_io(L);
<b> <font color="#FF0000">cdlua_open(L);</font>
</b>
lua_dofile("myprog.lua");
<b><font color="#FF0000">cdlua_close(L);</font></b>
lua_close(L);
}</pre>
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<p>The <font face="Courier New"><strong>cdlua_open</strong>()</font> function registers all CD functions and constants
your Lua program will need. The use of the CDLua functions in Lua is generally identical to their equivalents in C.
Nevertheless, there are several exceptions due to differences between the two languages. Notice that, as opposed to C,
in which the flags are<i> </i>combined with the bitwise operator OR, in Lua the flags are added arithmetically. </p>
<p>The CDLua dynamic libraries are also compatible with the Lua 5 "loadlib" function.<span lang="en-us">
</span>Here is an example on how to dynamically load CD
in Lua 5<span lang="en-us">.1</span>:</p>
<pre>local cdlua_open = package.loadlib("cdlua51.dll", "cdlua_open")
cdlua_open()</pre>
<p><strong>Lua</strong> 5.1 "require" can be used for all the <strong>
CDLua</strong>
libraries. You can use <b>require</b>"<b>cdlua</b>" and so on, but the LUA_CPATH
must also contains the following: </p>
<pre>"./lib?51.so;" [in UNIX]
".\\?51.dll;" [in Windows]
</pre>
<p>The LuaBinaries distribution already includes these modifications on the
default search path.</p>
<p>The simplest form <b>require</b>"<b>cd</b>"
and so on, can not be used because there are CD dynamic libraries with names
that will conflict with the names used by <b>require</b> during search.</p>
<h3><a name="New Functions">Function Names and Definitions</a></h3>
<p>In Lua, because of the name space "cd" all the functions and definitions have their names prefix changed. The
general rule is quite simple:</p>
<pre>cdXxx -> cd.Xxx
wdXxx -> cd.wXxx
CD_XXX -> cd.XXX</pre>
<h3>Modifications to the API</h3>
<p>New functions (without equivalents in C) were implemented to create and
destroy objects that do not exist in C. For instance functions were developed
to create and destroy images, pattern, stipple and palette. All the
metatables have the "tostring" method implemented to help debuging.</p>
<p>Some functions were modified to receive those objects as parameters.</p>
<p>Also the functions which receive values by reference in C were modified. Generally, the values of
parameters that would have their values modified are now returned by the function in the same order.</p>
<h3>Garbage Collection</h3>
<p>All the objects are garbage collected by the Lua garbage collector, except
the canvas because there can be different Lua canvases pointing to the same
C canvas. The tostring method of the Lua canvas will print both values, Lua
and C. The equal method will compare the C canvas value.</p>
<h3>Exchanging Values between C and Lua</h3>
<p>Because of some applications that interchange the use of CD canvases in Lua and C, we build a
few C functions that are available in "cdlua.h":</p>
<pre>cdCanvas* cdlua_checkcanvas(lua_State* L, int pos);
void cdlua_pushcanvas(lua_State* L, cdCanvas* canvas);</pre>
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