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 native C99 API that can be used with most game engines and scripting languages
• Modern type-safe C++11 API that doesn't rely on STL types
• Entire framework builds in less than 5 seconds.
• 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
• Run games on multiple CPU cores with a fast lockless scheduler and command queue
• First open source ECS with full support for entity relationships!
• Compiles warning-free on 8 compilers on all major platforms, with CI running more than 3000 tests
• No need to reinvent the wheel with fast native hierarchy, prefab and reflection implementations
• A web-based dashboard (click to try!) for exploring entities, running queries & learning Flecs:

You're looking at Flecs v3! While v3 stability is good, API changes can still happen.

Last stable v2 release: Flecs v2.4.8.

What is an Entity Component System?

ECS is a new way of organizing code and gameplay data that lets you build game worlds that are larger, more complex and are easier to extend. ECS is different in how it dynamically binds simulation logic ('systems') with game data ('components').

Something is typically 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

A simple example of this would be a game with two components, Position and Velocity, and a Move system that finds all entities with both components, and adds Velocity to Position.

For more info on ECS, check the ECS FAQ!

Getting Started

• Quickstart (docsforge)
• FAQ (docsforge)
• C examples
• C++ examples
• Manual (docsforge)
• Query Manual (docsforge)
• Relations Manual (docsforge)

Here is some awesome content provided by the community ❤️ :

• Bgfx/Imgui module
• Tower defense example
• Bringing Flecs to UE4
• Flecs + UE4 is magic
• Quickstart with Flecs in UE4
• Automatic component registration in UE4
• Building a space battle with Flecs in UE4
• Flecs + SDL + Web ASM example (live demo)
• Flecs + gunslinger example

Show me the code!

C99 example:

typedef struct {
  float x, y;
} Position, Velocity;

void Move(ecs_iter_t *it) {
  Position *p = ecs_term(it, Position, 1);
  Velocity *v = ecs_term(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_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_new_id(ecs);
  ecs_set(ecs, e, Position, {10, 20});
  ecs_set(ecs, e, 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()
    .set([](Position& p, Velocity& v) {
      p = {10, 20};
      v = {1, 2};
    });
    
  while (ecs.progress()) { }
}

Addons

Flecs has a modular architecture that makes it easy to only build the features you really need. By default all addons are built. To customize a build, first define FLECS_CUSTOM_BUILD, then add defines for the addons you need. For example:

#define FLECS_CUSTOM_BUILD  // Don't build all addons
#define FLECS_SYSTEM        // Build FLECS_SYSTEM

Here's an overview of all supported addons:

Addon	Description	Define
Cpp	C++11 API	FLECS_CPP
Module	Organize game logic into reusable modules	FLECS_MODULE
System	Create & run systems	FLECS_SYSTEM
Pipeline	Automatically schedule & multithread systems	FLECS_PIPELINE
Timer	Run systems at time intervals or at a rate	FLECS_TIMER
Meta	Flecs reflection system	FLECS_META
Meta_C	(C) Utilities for auto-inserting reflection data	FLECS_META_C
Expr	String format optimized for ECS data	FLECS_EXPR
JSON	JSON format	FLECS_JSON
Doc	Add documentation to components, systems & more	FLECS_DOC
Coredoc	Documentation for builtin components & modules	FLECS_COREDOC
Http	Tiny HTTP server for processing simple requests	FLECS_HTTP
Rest	REST API for showing entities in the browser	FLECS_REST
Parser	Create entities & queries from strings	FLECS_PARSER
Plecs	Small utility language for asset/scene loading	FLECS_PLECS
Rules	Powerful prolog-like query language	FLECS_RULES
Snapshot	Take snapshots of the world & restore them	FLECS_SNAPSHOT
Stats	See what's happening in a world with statistics	FLECS_STATS
Log	Extended tracing and error logging	FLECS_LOG
App	Flecs application framework	FLECS_APP
OS API Impl	Default OS API implementation for Posix/Win32	FLECS_OS_API_IMPL

Flecs Hub

Flecs Hub is a handy collection of repositories built with Flecs that showcase basic ways of how to build engine features like input handling, transformations 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.sdl2	SDL window creation & input management
flecs.systems.sokol	Sokol-based renderer

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!

• Lua
• Zig

Links

• Discord
• Medium
• ECS FAQ
• Twitter
• Reddit

Supporting Flecs ♥️

Supporting Flecs goes a long way towards keeping the project going and the community alive! If you like the project, consider:

• Giving it a star 🌟
• Becoming a sponsor: https://github.com/sponsors/SanderMertens