Flecs

A fast and lightweight Entity Component System that lets you build games and simulations with millions of entities.

Website | Source | Flecs-Hub: A collection of Flecs projects, modules and examples

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()) { }
}

Tags: gamedev   native   entity component system  

Last modified 23 December 2025