observers/two_components

• C

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  #include <two_components.h>
  #include <stdio.h>
   
  // An observer can match multiple components/tags. Only entities that match the
  // entire observer query will be forwarded to the callback. For example, an
  // observer for Position,Velocity won't match an entity that only has Position.
   
  typedef struct {
      double x, y;
  } Position, Velocity;
   
  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);
      Velocity *v = ecs_field(it, Velocity, 1);
   
      for (int i = 0; i < it->count; i ++) {
          ecs_entity_t e = it->entities[i];
          printf("%s: %s: %s: p: {%f, %f} v: {%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,
              v[i].x, v[i].y);
      }
  }
   
  int main(int argc, char *argv[]) {
      ecs_world_t *ecs = ecs_init_w_args(argc, argv);
   
      ECS_COMPONENT(ecs, Position);
      ECS_COMPONENT(ecs, Velocity);
   
      ECS_OBSERVER(ecs, Observer, EcsOnSet, Position, Velocity);
   
      // Create entity
      ecs_entity_t e = ecs_entity(ecs, { .name = "e" });
      
      // Set Position (emits EcsOnSet, does not yet match observer)
      ecs_set(ecs, e, Position, {10, 20});
   
      // Set Velocity (emits EcsOnSet, matches observer)
      ecs_set(ecs, e, Velocity, {1, 2});
   
      return ecs_fini(ecs);
   
      // Output:
      //   OnSet: Velocity: e: p: {10.000000, 20.000000} v: {1.000000, 2.000000}
  }

• C++

  View on GitHub

  #include <two_components.h>
  #include <iostream>
   
  // An observer can match multiple components/tags. Only entities that match the
  // entire observer query will be forwarded to the callback. For example, an
  // observer for Position,Velocity won't match an entity that only has Position.
   
  struct Position {
      double x, y;
  };
   
  struct Velocity {
      double x, y;
  };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      // Create observer for custom event
      ecs.observer<Position, Velocity>()
          .event(flecs::OnSet)
          .each([](flecs::iter& it, size_t i, Position& p, Velocity& v) {
              std::cout << " - " << it.event().name() << ": " 
                  << it.event_id().str() << ": "
                  << it.entity(i).name() << ": "
                  << "p: {" << p.x << ", " << p.y << "} "
                  << "v: {" << v.x << ", " << v.y << "}\n";
          });
   
      // Create entity, set Position (emits EcsOnSet, does not yet match observer)
      flecs::entity e = ecs.entity("e")
          .set<Position>({10, 20});
   
      // Set Velocity (emits EcsOnSet, matches observer)
      e.set<Velocity>({1, 2});
   
      // Output
      //   - OnSet: Velocity: e: p: {10, 20} v: {1, 2}
  }