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Cataclysm: Bright Nights

C++ Lua integration

This document describes implementation details behind Lua integration in Cataclysm: Bright Nights.

BN uses Lua 5.3.6 to run scripts and relies on sol2 v3.3.0 for bindings on C++ side.

C++ layout

Lua build can be enabled by passing LUA=1 to the Makefile, or enabling LUA build switch in CMake builds. Both msvc and android for simplicity always build with Lua enabled.

Lua source files

To simplify build setup and improve portability we bundle Lua 5.3.6 source code in src/lua/ directory and have the build systems compile it and link into the game executable and library for tests.

Sol2 source files

Sol2 makes it easy to bundle, we have sol2 v3.3.0 single-header amalgamated version in src/sol/ and just include it as needed. The header is quite large, so the less source files include it the better.

  • sol/config.hpp - Configuration header, we have a few options defined there
  • sol/forward.hpp - Forward declarations, a lightweight header that should be included in game headers instead of sol/sol.hpp
  • sol/sol.hpp - Main sol2 header file, quite large, avoid including in game headers

Game source files

All Lua-related game source files have the catalua prefix.

If you want to add new bindings, consider looking at existing examples in src/catalua_bindings.cpp and reading relevant part of Sol2 docs.

  • catalua.h (and catalua.cpp) - Main Lua interface. It’s the only header most of the codebase will have to include, and it provides a public interface that works in both LUA=1 and LUA=0 builds ( in builds without Lua, most of the functions there are no-op ).
  • catalua_sol.h and catalua_sol_fwd.h - Wrappers for sol/sol.hpp and sol/forward.hpp with custom pragmas to make them compile.
  • catalua_bindings* - Game Lua bindings live here.
  • catalua_console.h(.cpp) - Ingame Lua console.
  • catalua_impl.h(.cpp) - Implementation details for catalua.h(.cpp).
  • catalua_iuse_actor.h(.cpp) - Lua-driven iuse_actor.
  • catalua_log.h(.cpp) - In-memory logging for the console.
  • catalua_luna.h - Usertype registration interface with automatic doc generation, aka luna.
  • catalua_luna_doc.h - List of types registration through luna or exposed to its doc generator.
  • catalua_readonly.h(.cpp) - Functions for marking Lua tables as read-only.
  • catalua_serde.h(.cpp) - Lua table to/from JSON (de-)serialization.
  • catalua_type_operators.h - Macro that helps with implementing bindings for string_ids