flecs-luajit's Introduction

flecs-luajit

Introduction

A LuaJIT script host for the flecs entity component system. Keep in mind that the project is under development and the API might change unexpectedly.

Example

First the flecs module has to be imported and initialised

#include <flecs-luajit/module_base.h>
#include <flecs.h>

int main(void) {
    ecs_world_t* world = ecs_init();

    ECS_IMPORT(world, FlecsLuajitBase);
    ecs_luajit_init(world);

    ecs_luajit_run(world, &(ecs_luajit_run_desc_t) {
        .script = { .name = "example.lua" },
    });

    ecs_progress(world, 0.0f);
    return ecs_fini(world);
}

An example.lua script that imitates the example in the flecs readme

local flecs = require 'flecs'
local world = flecs.world

local ffi = require 'ffi'
ffi.cdef('typedef struct { ecs_f32_t x, y; } Position, Velocity;')

local Position = world:component {
    entity = world:entity { name = 'Position', symbol = 'Position' },
}

local Velocity = world:component {
    entity = world:entity { name = 'Velocity', symbol = 'Velocity' },
}

local e = world:entity { name = 'Bob' }
world:set(e, Position, { x = 10, y = 20 })
world:set(e, Velocity, { x = 1, y = 2 })

function Move(iter)
    for _, p, v in iter:each() do
        p.x = p.x + v.x
        p.y = p.y + v.y
    end
end

world:system {
    entity = world:entity {
        name = 'Move',
        add = { flecs.pair(flecs.g.DependsOn, flecs.g.OnUpdate) },
    },
    query = { filter = { expr = "Position, [in] Velocity" } },
    callback = 'Move',
}

Note that to make this example work with a multithreaded ecs_world_t one has to make some modifications to the Lua script. A more elaborate example can be found in the example directory.