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flecs-lua

This is a Lua binding for Flecs, it can be used to extend an application or as a standalone module.

Dependencies

  • Flecs v3.2.3 with most addons enabled - backward and forward compatibility is limited due to dependencies on semi-private API's

  • Lua 5.3 or later (requires 64-bit integers)

Build

Meson >= 0.55.0

meson build # -Dtests=enabled
cd build
ninja
ninja test

Lua API

Usage

Scripts are hosted by the FlecsLua module for the world it's imported into.

Using this library as a standalone Lua module is possible but is not the main focus of the project.

/* Creates a script host for the world */
ECS_IMPORT(world, FlecsLua);

/* Get a pointer to the VM */
lua_State *L = ecs_lua_get_state(world);

/* Execute init script, the world for all API calls is implicit */
luaL_dofile(L, argv[1]);

/* Lua systems will run on the main thread */
while(ecs_progress(world, 0))

Most of the functions are bound to their native counterparts, components are (de-)serialized to- and from Lua, it is not designed to be used with LuaJIT where FFI is preferred.

Components defined from the host with the meta module and from Lua are handled the same way and can be mixed in systems, queries, etc.

The script executed on init should be similar to the host's main().

main.lua

local ecs = require "ecs"
local m = require "module"

local ents = ecs.bulk_new(m.Position, 10)

for i in 1, #ents do
    ecs.set(ents[i], m.Position, { x = i * 2, y = i * 3})
end

Modules can be stuctured like normal Lua modules.

Importing native modules or other Lua scripts is left to the host application. ecs.import() does not load flecs modules, instead it returns a table with all components and named entities from an already imported flecs module.

Flecs modules are defined and imported with ecs.module(), it takes an import callback which is called immediately and returns the imported module ID. All components and entities should be registered inside the callback function for proper scoping.

module.lua

local ecs = require "ecs"
local m = {}

function m.system(it)

    for p, e in ecs.each(it) do
        print("entity: " .. e)
        p.x = p.x + 1
        p.y = p.y + 1
    end
end

ecs.module("name", function()

    m.Position = ecs.struct("Position", "{float x; float y;}")

    ecs.system(m.system, "Move", ecs.OnUpdate, "Position")

end)

return m

Debugging

For debug builds (#ifndef NDEBUG) most API functions will retrieve the current file, source line and expose them through ar.short_src and ar.currentline. Set watches for these variables to track where API functions are called from in Lua.

Lua state lifecycle

  • A default Lua state is created when the module is imported

  • To set a custom lua_State use ecs_lua_set_state(), this will destroy the default state.

  • In both cases lua_close() is called on ecs_fini() to trigger __gc metamethods before the world is destroyed.