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:

Fast and portable zero dependency C99 API
Modern type-safe C++17 API that doesn't use STL containers
First open source ECS with full support for Entity Relationships!
Fast native support for hierarchies and prefabs
Code base that builds in less than 5 seconds
Runs in the browser without modifications with emscripten
Cache friendly archetype/SoA storage that can process millions of entities every frame
Automatic component registration that works out of the box across shared libraries/DLLs
Write free functions with queries or run code automatically in systems
Run games on multiple CPU cores with a fast lockless scheduler
Verified on all major compilers and platforms with CI running more than 13000 tests
Integrated reflection framework with JSON serializer and support for runtime components
Unit annotations for components
Powerful query language with support for joins and inheritance
Statistics addon for profiling ECS performance
A web-based UI for monitoring & controlling your apps:

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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!

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, 0);
  Velocity *v = ecs_field(it, Velocity, 1);

  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_world_t *ecs = ecs_init();

  ECS_COMPONENT(ecs, Position);
  ECS_COMPONENT(ecs, Velocity);

  ECS_SYSTEM(ecs, Move, EcsOnUpdate, Position, Velocity);

  ecs_entity_t e = ecs_insert(ecs,
    ecs_value(Position, {10, 20}),
    ecs_value(Velocity, {1, 2}));

  while (ecs_progress(ecs, 0)) { }
}

Same example in C++:

struct Position {
  float x, y;
};

struct Velocity {
  float x, y;
};

int main(int argc, char *argv[]) {
  flecs::world ecs;

  ecs.system<Position, const Velocity>()
    .each([](Position& p, const Velocity& v) {
      p.x += v.x;
      p.y += v.y;
    });

  auto e = ecs.entity()
    .insert([](Position& p, Velocity& v) {
      p = {10, 20};
      v = {1, 2};
    });

  while (ecs.progress()) { }
}

Projects using Flecs

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

Tempest Rising

Territory Control 2

Resistance is Brutal

Rescue Ops: Wildfire

Age of Respair

FEAST

Gloam Vault

Antimatcher

Writ of Battle

Extermination Shock

The Forge

ECS survivors

Tome Tumble Tournament

Sol Survivor

After Sun

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!

C#:
- BeanCheeseBurrito/Flecs.NET
Rust:
- Flecs-Rust
- flecs-polyglot
Zig:
- zig-gamedev/zflecs
Lua:
- sro5h/flecs-luajit
- flecs-hub/flecs-lua
Clojure
- vybe-flecs

Flecs

Install / Use

README