Re: 3D Vectors

[Luiz Henrique de Figueiredo <lhf@...>]

>Since a number of people are using Lua for game scripting, I thought
>I'd ask: has anyone come up with a clever way for adding support
>for 3D vectors (an array of 3 floats: x, y, and z) to Lua? My current
>solution seems to use an awful lot of code just to add one new data type.

I'm surprised you say "an awful lot of code".
I include below a sample library for 3D vectors, and it's pretty simple.
Unless I'm missing something...

Here is some code 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...

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

/*
* 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;
}