void Push(Vec3 var)
{
   Vec3 *ubox = (Vec3 *)lua_newuserdata(lua->L, sizeof(Vec3));
   *ubox = var;
   luaL_getmetatable(lua->L, meta_name);
   lua_setmetatable(lua->L, -2);
}

Vec3 *Get(int index)
{
   Vec3 var = *(Vec3 *)luaL_checkudata(L, 1, "Vec3");
   return var;
}