Flecs – A fast entity component system for C and C++

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:

Flecs Explorer

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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!

Flecs playground

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

Documentation

Performance

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

ecs_set(ecs, e, Position, {10, 20});

ecs_set(ecs, e, Velocity, {1, 2});

}

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.

ecs_id_t ecs_entity_t

An entity identifier.

struct ecs_world_t ecs_world_t

A world is the container for all ECS data and supporting features.

ecs_entity_t ecs_new_id(ecs_world_t *world)

Create new entity id.

#define ECS_COMPONENT(world, id)

Declare & define a component.

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;

});

.set([](Position& p, Velocity& v) {

p = {10, 20};

v = {1, 2};

});

while (ecs.progress()) { }

}

void each(Func &&func) const

Iterate over all entities with components in argument list of function.

flecs::entity entity(Args &&... args) const

Create an entity.

flecs::system system(flecs::entity e) const

Upcast entity to a system.

Projects using Flecs

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

Territory Control

https://store.steampowered.com/app/690290/Territory_Control_2/

Sol Survivor

https://nicok.itch.io/sol-survivor-demo

The Forge

https://github.com/ConfettiFX/The-Forge

Equilibrium Engine

https://github.com/clibequilibrium/EquilibriumEngine

Gravitas

https://thepunkcollective.itch.io/gravitas

After Sun

https://github.com/foxnne/aftersun

Tower defense (open source demo)

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

Procedural City (open source demo)

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

Resources

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.

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!

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