observers/custom_event

• C

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  #include <custom_event.h>
  #include <stdio.h>
   
  // Observers can be used to match custom events. Custom events can be emitted
  // using the ecs_emit function. This function is also used by builtin events,
  // so builtin and custom events use the same rules for matching with observers.
  //
  // An event consists out of three pieces of data used to match with observers:
  //  - An single event kind (EcsOnAdd, EcsOnRemove, ...)
  //  - One or more event ids (Position, Velocity, ...)
  //  - A source (either an entity or a table)
   
  typedef struct {
      double x, y;
  } Position;
   
  void Observer(ecs_iter_t *it) {
      ecs_world_t *ecs = it->stage;
      
      // The event kind
      ecs_entity_t event = it->event;
   
      // The (component) id for which the event was emitted
      ecs_entity_t event_id = it->event_id;
   
      for (int i = 0; i < it->count; i ++) {
          ecs_entity_t e = it->entities[i];
   
          printf(" - %s: %s: %s\n", 
              ecs_get_name(ecs, event), 
              ecs_get_name(ecs, event_id),
              ecs_get_name(ecs, e));
      }
  }
   
  int main(int argc, char *argv[]) {
      ecs_world_t *ecs = ecs_init_w_args(argc, argv);
   
      ECS_COMPONENT(ecs, Position);
   
      // Create custom event
      ecs_entity_t MyEvent = ecs_entity(ecs, { .name = "MyEvent" });
   
      // Create observer for custom event
      ECS_OBSERVER(ecs, Observer, MyEvent, Position);
   
      // Create entity
      ecs_entity_t e = ecs_entity(ecs, { .name = "e" });
      
      // The observer query can be matched against the entity, so make sure it
      // has the Position component before emitting the event. This does not 
      // trigger the observer yet.
      ecs_set(ecs, e, Position, {10, 20});
   
      // Emit the custom event
      ecs_emit(ecs, &(ecs_event_desc_t) {
          .event = MyEvent,
          .ids = &(ecs_type_t){ (ecs_id_t[]){ ecs_id(Position) }, 1 }, // 1 id
          .entity = e
      });
   
      ecs_fini(ecs);
   
      // Output
      //    - MyEvent: Position: e
  }

• C++

  View on GitHub

  #include <custom_event.h>
  #include <iostream>
   
  // Observers can be used to match custom events. Custom events can be emitted
  // using the ecs_emit function. This function is also used by builtin events,
  // so builtin and custom events use the same rules for matching with observers.
  //
  // An event consists out of three pieces of data used to match with observers:
  //  - An single event kind (EcsOnAdd, EcsOnRemove, ...)
  //  - One or more event ids (Position, Velocity, ...)
  //  - A source (either an entity or a table)
   
  struct Position {
      double x, y;
  };
   
  // Create tag type to use as event (could also use entity)
  struct MyEvent { };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      // Create observer for custom event
      ecs.observer<Position>()
          .event<MyEvent>()
          .each([](flecs::iter& it, size_t i, Position&) {
              std::cout << " - " << it.event().name() << ": " 
                  << it.event_id().str() << ": "
                  << it.entity(i).name() << "\n";
          });
   
      // The observer query can be matched against the entity, so make sure it
      // has the Position component before emitting the event. This does not 
      // trigger the observer yet.
      flecs::entity e = ecs.entity("e")
          .set<Position>({10, 20});
   
      // Emit the custom event
      ecs.event<MyEvent>()
          .id<Position>()
          .entity(e)
          .emit();
   
      // Output
      //   - MyEvent: Position: e
  }