queries/singleton

• C

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  #include <singleton.h>
  #include <stdio.h>
   
  // This example shows how to use singleton components in queries.
   
  // Singleton component
  typedef struct {
      double value; 
  } Gravity;
   
  // Entity component
  typedef struct {
      double x, y;
  } Velocity;
   
  int main(int argc, char *argv[]) {
      ecs_world_t *ecs = ecs_init_w_args(argc, argv);
   
      ECS_COMPONENT(ecs, Velocity);
      ECS_COMPONENT(ecs, Gravity);
   
      // Mark Gravity as singleton
      ecs_add_id(ecs, ecs_id(Gravity), EcsSingleton);
   
      // Set singleton
      ecs_singleton_set(ecs, Gravity, { 9.81 });
   
      ecs_entity_t e1 = ecs_entity(ecs, { .name = "e1" });
      ecs_entity_t e2 = ecs_entity(ecs, { .name = "e2" });
      ecs_entity_t e3 = ecs_entity(ecs, { .name = "e3" });
   
      // Set Velocity
      ecs_set(ecs, e1, Velocity, {0, 0});
      ecs_set(ecs, e2, Velocity, {0, 1});
      ecs_set(ecs, e3, Velocity, {0, 2});
   
      // Create query that matches Gravity singleton
      ecs_query_t *q = ecs_query(ecs, {
          .terms = {
              { .id = ecs_id(Velocity) },
              { .id = ecs_id(Gravity) }
          }
      });
   
      ecs_iter_t it = ecs_query_iter(ecs, q);
      while (ecs_query_next(&it)) {
          Velocity *v = ecs_field(&it, Velocity, 0);
          Gravity *g = ecs_field(&it, Gravity, 1);
   
          for (int i = 0; i < it.count; i ++) {
              // Make sure to access g as a pointer, as we only have a single
              // instance of the Gravity component.
              v[i].y += g->value;
   
              printf("%s velocity is {%f, %f}\n",
                  ecs_get_name(ecs, it.entities[i]), v[i].x, v[i].y);
          }
      }
   
      // Output
      //   e1 velocity is {0.000000, 9.810000}
      //   e2 velocity is {0.000000, 10.810000}
      //   e3 velocity is {0.000000, 11.810000}
   
      ecs_fini(ecs);
  }

• C++

  View on GitHub

  #include <singleton.h>
  #include <iostream>
   
  // This example shows how to use singleton components in queries.
   
  // Singleton component
  struct Gravity {
      double value; 
  };
   
  // Entity component
  struct Velocity {
      double x;
      double y;
  };
   
  int main(int, char *[]) {
      flecs::world world;
   
      // Mark Gravity as singleton
      world.component<Gravity>().add(flecs::Singleton);
   
      // Set singleton
      world.set<Gravity>({ 9.81 });
   
      // Set Velocity
      world.entity("e1").set<Velocity>({0, 0});
      world.entity("e2").set<Velocity>({0, 1});
      world.entity("e3").set<Velocity>({0, 2});
   
      // Create query that matches Gravity singleton
      flecs::query<Velocity, const Gravity> q = 
          world.query<Velocity, const Gravity>();
   
      q.each([](flecs::entity e, Velocity& v, const Gravity& g) {
          v.y += g.value;
          std::cout << e.path() << " velocity is {" 
              << v.x << ", " << v.y << "}" << std::endl;
      });
   
      // Output
      //   ::e1 velocity is {0, 9.81}
      //   ::e2 velocity is {0, 10.81}
      //   ::e3 velocity is {0, 11.81}
  }