How to expose C++ functions to a lua script?

@jeanie_reilly 

To expose C++ functions to a Lua script, you need to use a Lua C API, which provides functions to interact with Lua from C++. Here are the basic steps to do so:

1. Include the Lua header file in your C++ code:

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extern "C" {
#include "lua.h"
#include "lauxlib.h"
#include "lualib.h"
}

1. Define a C++ function that you want to expose to Lua. For example:

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int add(lua_State* L) {
  double a = luaL_checknumber(L, 1);
  double b = luaL_checknumber(L, 2);
  lua_pushnumber(L, a + b);
  return 1;
}

This function takes two arguments from the Lua stack, adds them together, and pushes the result back onto the stack.

1. Create a Lua state and register the function with Lua:

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lua_State* L = luaL_newstate();
luaL_openlibs(L);
lua_pushcfunction(L, add);
lua_setglobal(L, "add");

This creates a new Lua state, loads the standard Lua libraries, registers the add function with Lua, and assigns it a global name add.

1. Call the function from a Lua script:

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result = add(1, 2)
print(result)

This calls the add function with two arguments, prints the result to the console.

Note: This is just a basic example, and there are many other ways to expose C++ functions to Lua. You may want to use a library such as LuaBridge or LuaBind to simplify the process.