observers/yield_existing

• C

  View on GitHub

  #include <yield_existing.h>
  #include <stdio.h>
   
  // Observers can enable a "yield_existing" feature that upon creation of the
  // observer produces events for all entities that match the observer query. The
  // feature is only implemented for the builtin EcsOnAdd and EcsOnSet events.
   
  typedef struct {
      double x, y;
  } Position;
   
  void Observer(ecs_iter_t *it) {
      ecs_world_t *ecs = it->stage;
   
      ecs_entity_t event = it->event;
      ecs_entity_t event_id = it->event_id;
      Position *p = ecs_field(it, Position, 0);
   
      for (int i = 0; i < it->count; i ++) {
          ecs_entity_t e = it->entities[i];
          printf(" - %s: %s: %s: {%f, %f}\n", 
              ecs_get_name(ecs, event), 
              ecs_get_name(ecs, event_id),
              ecs_get_name(ecs, e),
              p[i].x, p[i].y);
      }
  }
   
  int main(int argc, char *argv[]) {
      ecs_world_t *ecs = ecs_init_w_args(argc, argv);
   
      ECS_COMPONENT(ecs, Position);
   
      // Create existing entities with Position component
      ecs_entity_t e1 = ecs_entity(ecs, { .name = "e1" });
      ecs_set(ecs, e1, Position, {10, 20});
      ecs_entity_t e2 = ecs_entity(ecs, { .name = "e2" });
      ecs_set(ecs, e2, Position, {20, 30});
   
      ecs_observer(ecs, {
          .query.terms = {{ .id = ecs_id(Position) }},
          .events = { EcsOnSet },
          .callback = Observer,
          .yield_existing = true // Trigger for existing matching entities
      });
   
      ecs_fini(ecs);
   
      // Output
      //   - OnSet: Position: e1: {10.000000, 20.000000}
      //   - OnSet: Position: e2: {20.000000, 30.000000}
  }

• C++

  View on GitHub

  #include <yield_existing.h>
  #include <iostream>
   
  // Observers can enable a "yield_existing" feature that upon creation of the
  // observer produces events for all entities that match the observer query. The
  // feature is only implemented for the builtin EcsOnAdd and EcsOnSet events.
   
  struct Position {
      double x, y;
  };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      // Create existing entities with Position component
      ecs.entity("e1").set<Position>({10, 20});
      ecs.entity("e2").set<Position>({20, 30});
   
      // Create an observer for three events
      ecs.observer<Position>()
          .event(flecs::OnSet)
          .yield_existing() // Trigger for existing matching entities
          .each([](flecs::iter& it, size_t i, Position& p) {
              std::cout << " - " << it.event().name() << ": " 
                  << it.event_id().str() << ": "
                  << it.entity(i).name() 
                  << ": {" << p.x << ", " << p.y << "}\n";
          });
   
      // Output
      //   - OnSet: Position: e1: {10, 20}
      //   - OnSet: Position: e2: {20, 30}
  }