This is a very simple example of wrapping some vector code. The function lua_vec3libopen() uses luaL_openl() to add a global function vector3(), a vector constructor. A tag is created so that the tag methods gettable() and settable() can be used to access elements in the vector. See the test code for usage.
[!] VersionNotice: The below code pertains to an older Lua version, Lua 4. Certain features used like tag methods (settagmethod) are no longer present in Lua 5 but have been replaced with metamethods.
Caveat: The code below uses a static variable TAG. This can be avoided, and should. I should have used the registry but I was lazy. I could also have used TAG local to lua_vec3libopen() and used it as an upvalue to vec3new(). I was also lazy in my treatment of field names: I only look at the first letter. --lhf
This code is for Lua 4.0. I've updated it for Lua 5.0 [here]. --lhf
/*
* vec3lib.c
* add 3d vectors to Lua
* this code is in the public domain
*/
#include "lua.h"
#include "lauxlib.h"
LUALIB_API int lua_vec3libopen (lua_State *L);
typedef struct { double a[3]; } Vector3;
static int TAG; /* lazy! */
static int vec3new(lua_State *L) {
Vector3* v;
lua_newuserdata(L,sizeof(Vector3));
lua_settag(L,TAG);
v=lua_touserdata(L,-1);
if (lua_gettop(L)>1) {
v->a[0]=luaL_check_number(L,1);
v->a[1]=luaL_check_number(L,2);
v->a[2]=luaL_check_number(L,3);
}
else
v->a[0] = v->a[1] = v->a[2] = 0;
return 1;
}
static int vec3get(lua_State *L) {
Vector3* v=lua_touserdata(L,1);
const char* i=luaL_check_string(L,2);
switch (*i) { /* lazy! */
case 'x': case 'r': lua_pushnumber(L,v->a[0]); break;
case 'y': case 'g': lua_pushnumber(L,v->a[1]); break;
case 'z': case 'b': lua_pushnumber(L,v->a[2]); break;
default: lua_pushnumber(L,0.0); break;
}
return 1;
}
static int vec3set(lua_State *L) {
Vector3* v=lua_touserdata(L,1);
const char* i=luaL_check_string(L,2);
double t=luaL_check_number(L,3);
switch (*i) { /* lazy! */
case 'x': case 'r': v->a[0]=t; break;
case 'y': case 'g': v->a[1]=t; break;
case 'z': case 'b': v->a[2]=t; break;
default: break;
}
return 1;
}
static const struct luaL_reg vec3lib[] = {
{"vector3", vec3new},
};
int lua_vec3libopen (lua_State *L) {
luaL_openl(L,vec3lib);
TAG=lua_newtag(L);
lua_pushcfunction(L,vec3get); lua_settagmethod(L,TAG,"gettable");
lua_pushcfunction(L,vec3set); lua_settagmethod(L,TAG,"settable");
return 0;
}
The following code can be used to test it:
-- a = vector3() a = vector3(10,20,30) print(a,tag(a)) print(a.x,a.y,a.z) print(a.t,a[1]) a.x,a.y,a.z=100,200,300 print(a.x,a.y,a.z) -- try also a.r, a.g, a.b, if you want to use vectors to store colors...