queries/component_inheritance

• C

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  #include <component_inheritance.h>
  #include <stdio.h>
   
  // This example shows how queries can be used to match simple inheritance trees.
   
  int main(int argc, char *argv[]) {
      ecs_world_t *ecs = ecs_init_w_args(argc, argv);
   
      // Create a simple hierarchy of unit types.
   
      ECS_TAG(ecs, Unit);
      ecs_entity_t CombatUnit = ecs_entity(ecs, { .name = "CombatUnit" });
      ecs_add_pair(ecs, CombatUnit, EcsIsA, Unit);
      ecs_entity_t MeleeUnit = ecs_entity(ecs, { .name = "MeleeUnit" });
      ecs_add_pair(ecs, MeleeUnit, EcsIsA, CombatUnit);
      ecs_entity_t RangedUnit = ecs_entity(ecs, { .name = "RangedUnit" });
      ecs_add_pair(ecs, RangedUnit, EcsIsA, CombatUnit);
   
      ecs_entity_t Warrior = ecs_entity(ecs, { .name = "Warrior" });
   
      ecs_add_pair(ecs, Warrior, EcsIsA, MeleeUnit);
      ecs_entity_t Wizard = ecs_entity(ecs, { .name = "Wizard" });
      ecs_add_pair(ecs, Wizard, EcsIsA, RangedUnit);
      ecs_entity_t Marksman = ecs_entity(ecs, { .name = "Marksman" });
      ecs_add_pair(ecs, Marksman, EcsIsA, RangedUnit);
      ecs_entity_t Builder = ecs_entity(ecs, { .name = "Builder" });
      ecs_add_pair(ecs, Builder, EcsIsA, Unit);
   
      // Create a few units
      ecs_entity_t warrior_1 = ecs_entity(ecs, { .name = "warrior_1" });
      ecs_add_id(ecs, warrior_1, Warrior);
      ecs_entity_t warrior_2 = ecs_entity(ecs, { .name = "warrior_2" });
      ecs_add_id(ecs, warrior_2, Warrior);
   
      ecs_entity_t marksman_1 = ecs_entity(ecs, { .name = "marksman_1" });
      ecs_add_id(ecs, marksman_1, Marksman);
      ecs_entity_t marksman_2 = ecs_entity(ecs, { .name = "marksman_2" });
      ecs_add_id(ecs, marksman_2, Marksman);
   
      ecs_entity_t wizard_1 = ecs_entity(ecs, { .name = "wizard_1" });
      ecs_add_id(ecs, wizard_1, Wizard);
      ecs_entity_t wizard_2 = ecs_entity(ecs, { .name = "wizard_2" });
      ecs_add_id(ecs, wizard_2, Wizard);
   
      ecs_entity_t builder_1 = ecs_entity(ecs, { .name = "builder_1" });
      ecs_add_id(ecs, builder_1, Builder);
      ecs_entity_t builder_2 = ecs_entity(ecs, { .name = "builder_2" });
      ecs_add_id(ecs, builder_2, Builder);
   
      // Create a query to find all ranged units
      ecs_query_t *q = ecs_query(ecs, {
          .terms = {{ .id = RangedUnit }}
      });
   
      // Iterate the query
      ecs_iter_t it = ecs_query_iter(ecs, q);
      while (ecs_query_next(&it)) {
          for (int i = 0; i < it.count; i ++) {
              printf("Unit %s found\n", ecs_get_name(ecs, it.entities[i]));
          }
      }
   
      ecs_query_fini(q);
   
      // Output
      //  Unit wizard_1 found
      //  Unit wizard_2 found
      //  Unit marksman_1 found
      //  Unit marksman_2 found
   
      return ecs_fini(ecs);
  }

• C++

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  #include <component_inheritance.h>
  #include <iostream>
   
  // This example shows how queries can be used to match simple inheritance trees.
   
  struct Unit { };
  struct CombatUnit : Unit { };
  struct MeleeUnit : CombatUnit { };
  struct RangedUnit : CombatUnit { };
   
  struct Warrior : MeleeUnit { };
  struct Wizard : RangedUnit { };
  struct Marksman : RangedUnit { };
  struct Builder : Unit { };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      // Make the ECS aware of the inheritance relationships. Note that IsA
      // relationship used here is the same as in the prefab example.
      ecs.component<CombatUnit>().is_a<Unit>();
      ecs.component<MeleeUnit>().is_a<CombatUnit>();
      ecs.component<RangedUnit>().is_a<CombatUnit>();
   
      ecs.component<Warrior>().is_a<MeleeUnit>();
      ecs.component<Wizard>().is_a<RangedUnit>();
      ecs.component<Marksman>().is_a<RangedUnit>();
      ecs.component<Builder>().is_a<Unit>();
   
      // Create a few units
      ecs.entity("warrior_1").add<Warrior>();
      ecs.entity("warrior_2").add<Warrior>();
   
      ecs.entity("marksman_1").add<Marksman>();
      ecs.entity("marksman_2").add<Marksman>();
   
      ecs.entity("wizard_1").add<Wizard>();
      ecs.entity("wizard_2").add<Wizard>();
   
      ecs.entity("builder_1").add<Builder>();
      ecs.entity("builder_2").add<Builder>();
   
      // Create a query to find all ranged units
      flecs::query<RangedUnit> q = ecs.query<RangedUnit>();
   
      // Iterate the query
      q.each([](flecs::entity e, RangedUnit) {
          std::cout << "Unit " << e.name() << " found\n";
      });
   
      // Output:
      //   Unit wizard_1 found
      //   Unit wizard_2 found
      //   Unit marksman_1 found
      //   Unit marksman_2 found
  }