Flecs v3.2
A fast entity component system (ECS) for C & C++
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Version MIT Documentation actions Discord Chat

Flecs is a fast and lightweight Entity Component System that lets you build games and simulations with millions of entities (join the Discord!). Here are some of the framework's highlights:

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What is an Entity Component System?

ECS is a way of organizing code and data that lets you build games that are larger, more complex and are easier to extend. Something is called an ECS when it:

  • Has entities that uniquely identify objects in a game
  • Has components which are datatypes that can be added to entities
  • Has systems which are functions that run for all entities matching a component query

For more information, check the ECS FAQ!

Try it out!

The Flecs playground lets you try Flecs without writing any C/C++ code!

To learn how to use the playground, check the Flecs Script Tutorial.



For a list of regularly tracked benchmarks, see the ECS Benchmark project.

Show me the code!

C99 example:

typedef struct {
float x, y;
} Position, Velocity;
void Move(ecs_iter_t *it) {
Position *p = ecs_field(it, Position, 1);
Velocity *v = ecs_field(it, Velocity, 2);
for (int i = 0; i < it->count; i++) {
p[i].x += v[i].x;
p[i].y += v[i].y;
int main(int argc, char *argv[]) {
ECS_COMPONENT(ecs, Position);
ECS_COMPONENT(ecs, Velocity);
ECS_SYSTEM(ecs, Move, EcsOnUpdate, Position, Velocity);
ecs_set(ecs, e, Position, {10, 20});
ecs_set(ecs, e, Velocity, {1, 2});
while (ecs_progress(ecs, 0)) { }
FLECS_API bool ecs_progress(ecs_world_t *world, ecs_ftime_t delta_time)
Progress a world.
#define ECS_SYSTEM(world, id, phase,...)
Declare & define a system.
Definition system.h:137
ecs_id_t ecs_entity_t
An entity identifier.
Definition flecs.h:318
struct ecs_world_t ecs_world_t
A world is the container for all ECS data and supporting features.
Definition flecs.h:362
ecs_entity_t ecs_new_id(ecs_world_t *world)
Create new entity id.
#define ECS_COMPONENT(world, id)
Declare & define a component.
Definition flecs_c.h:145
ecs_world_t * ecs_init(void)
Create a new world.

Same example in C++11:

struct Position {
float x, y;
struct Velocity {
float x, y;
int main(int argc, char *argv[]) {
ecs.system<Position, const Velocity>()
.each([](Position& p, const Velocity& v) {
p.x += v.x;
p.y += v.y;
auto e = ecs.entity()
.set([](Position& p, Velocity& v) {
p = {10, 20};
v = {1, 2};
while (ecs.progress()) { }
flecs::system system(flecs::entity e) const
Upcast entity to a system.
flecs::entity entity(Args &&... args) const
Create an entity.
bool progress(ecs_ftime_t delta_time=0.0) const
Progress world one tick.
The world.
Definition world.hpp:132

Projects using Flecs

If you have a project you'd like to share, let me know on Discord!


‍We knew that we wanted to build Hytale around an Entity-Component-System (ECS). When we analyzed the options, FLECS rose to the top. FLECS provides the backbone of the Hytale Game Engine. Its flexibility has allowed us to build highly varied gameplay while supporting our vision for empowering Creators.

– Dann Webster, Hypixel studios

Tempest Rising

Territory Control

The Forge

Extermination Shock

Sol Survivor

Equilibrium Engine


After Sun

Flecs Demo's

https://www.flecs.dev/tower_defense/etc (repository)

https://www.flecs.dev/city (repository)


Resources provided by the community :heart:

Flecs around the web

Flecs Hub

Flecs Hub is a collection of repositories that show how Flecs can be used to build game systems like input handling, hierarchical transforms and rendering.

Module Description
flecs.components.cglm Component registration for cglm (math) types
flecs.components.input Components that describe keyboard and mouse input
flecs.components.transform Components that describe position, rotation and scale
flecs.components.physics Components that describe physics and movement
flecs.components.geometry Components that describe geometry
flecs.components.graphics Components used for computer graphics
flecs.components.gui Components used to describe GUI components
flecs.systems.transform Hierarchical transforms for scene graphs
flecs.systems.physics Systems for moving objects and collision detection
flecs.systems.sokol Sokol-based renderer
flecs.game Generic game systems, like a camera controller

Language bindings

The following language bindings have been developed with Flecs! Note that these are projects built and maintained by helpful community members, and may not always be up to date with the latest commit from master!