All of the code that we have written so far has been about exposing C to Lua using Lua Bridge. Any C function exposed through Lua Bridge can be called from Lua. If a function is in a namespace and not a class, it is called with the dot syntax: Math.Sqrt(16). But, if a function is in a class, it needs to be called with the colon syntax: vector:Normalize(). The following code shows how to expose a C function to Lua and how to call it from Lua.

The C code needs to declare the appropriate vector 3 class, a Normalize member function, and a global dot product function. Next, the Register function exposes all of these functions to Lua, using Lua Bridge:

class Vec3 {
  public:
    float x, y, z;
    
    float Normalize() {
        float dot = x * x + y * y + z * z;
        if (dot == 0) {
            return 0;
        }
        return sqrt(dot);
    }
}

float Dot(Vec3 a, Vec3 b) {
    return a.x * b.x + a.y * b.y + a.z * b.z;
}

void Register(lua_State* L) {
    getGlobalNamespace(L)
      .beginNamespace("Math")
          .beginClass<Vec3>("Vec3")
              .addData("x", &Vec3::x)
              .addData("y", &Vec3::y)
              .addData("z", &Vec3::z)
              .addFunction("Normalize", &Vec3::Normalize)
          .endClass()
          .addFunction("Dot", Dot)
      .endNameSpace();
}

The Lua file can create new vectors, and can then set the x, y, or z members of each vector. Then, the Dot and Normalize functions can be called. The following code sample does this:

local a = Math.Vec3()
local b = Math.Vec3()

a.x = 7
b.x = 3

print ("Dot: " .. Dot(a, b));

print ("Normalize both");
a:Normalize()
b:Normalize()

print ("Dot: " .. Dot(a, b));