example.c

struct game_manager {
    struct rng rng;
    struct sprite_atlas atlas;
    struct scene scene;
    struct creature player;
    struct input_manager input_manager;
};

void game_manager_init(struct game_manager* self) {
    srand(time(NULL));
    rng_init(&self->rng, rand());
    sprite_atlas_init(&self->atlas, "/data/Assets/...tileset.v4.png", 16, 16);
    creature_init(&self->player, 161);
    scene_init(&self->scene, &self->rng, &self->player, 15, 20);
    input_manager_init(&self->input_manager);
    event_emitter_subscribe(&self->input_manager.events,
        self, (void (*)(void*, void*, void*))game_manager_handle_event);
    event_emitter_subscribe(&self->player.events,
        self, (void (*)(void*, void*, void*))game_manager_handle_event);
}

// ...other game_manager stuff...

void game_manager_free(struct game_manager* self) {
    creature_free(&self->player);
    scene_free(&self->scene);
    sprite_atlas_free(&self->atlas);
    input_manager_free(&self->input_manager);
}

/////////////////////////////////////////////////////////////////////////////

struct input_manager {
    bool is_movement_input_present;
    enum direction movement_input_direction;
    struct event_emitter events;
};

void input_manager_init(struct input_manager* self) {
    self->is_movement_input_present = false;
    self->movement_input_direction = DIR_NONE;
    event_emitter_init(&self->events);
}

// ...other input_manager stuff...

void input_manager_free(struct input_manager* self) {
    event_emitter_free(&self->events);
}

////////////////////////////////////////////////////////////////////////////


struct event_emitter_listener {
    void (*callback)(void*, void*, void*);
    void *context;
};

struct event_emitter {
    int listeners_count;
    struct event_emitter_listener* listeners;
};

void event_emitter_init(struct event_emitter* self) {
    self->listeners_count = 0;
    self->listeners = malloc(2 * sizeof(struct event_emitter_listener));
}

void event_emitter_subscribe(struct event_emitter* self, void* context, void (*callback)(void*, void*, void*)) {
    int n = self->listeners_count;
    if (n > 0 && (n & (n - 1)) == 0) {
        self->listeners = realloc(self->listeners, 2 * n * sizeof(struct event_emitter_listener));
    }
    self->listeners[self->listeners_count] = (struct event_emitter_listener) {
        .callback = callback,
        .context = context,
    };
    self->listeners_count++;
}

void event_emitter_emit(struct event_emitter* self, void* sender, void* event) {
    for (int i = 0; i < self->listeners_count; i++) {
        struct event_emitter_listener* listener = &self->listeners[i];
        listener->callback(listener->context, sender, event);
    }
}

void event_emitter_free(struct event_emitter* self) {
    free(self->listeners);
}