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++11 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 8000 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++11:

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!

Hytale

‍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

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:
Zig:
Lua:
- sro5h/flecs-luajit
- flecs-hub/flecs-lua

What is an Entity Component System?

Show me the code!

Projects using Flecs

Hytale

Tempest Rising

Territory Control 2

Resistance is Brutal

Age of Respair

The Forge

Extermination Shock

Tome Tumble Tournament

Hyperion Minecraft Server

Sol Survivor

Equilibrium Engine

After Sun

Flecs Demo's

Flecs Hub

Language bindings