hello_world

• C

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  #include <hello_world.h>
  #include <stdio.h>
   
  typedef struct {
      double x;
      double y;
  } Position, Velocity;
   
  /* Move system implementation. System callbacks may be called multiple times,
   * as entities are grouped in tables by which components they have, and each 
   * table has its own set of component arrays. */
  void Move(ecs_iter_t *it) {
      Position *p = ecs_field(it, Position, 0);
      Velocity *v = ecs_field(it, Velocity, 1);
   
      /* Print the set of components for the iterated over entities */
      char *type_str = ecs_table_str(it->stage, it->table);
      printf("Move entities with [%s]\n", type_str);
      ecs_os_free(type_str);
   
      /* Iterate entities for the current table */
      for (int i = 0; i < it->count; i ++) {
          p[i].x += v[i].x;
          p[i].y += v[i].y;
      }
  }
   
  int main(int argc, char *argv[]) {
      /* Create the world */
      ecs_world_t *world = ecs_init_w_args(argc, argv);
   
      /* Register components */
      ECS_COMPONENT(world, Position);
      ECS_COMPONENT(world, Velocity);
   
      /* Register system */
      ECS_SYSTEM(world, Move, EcsOnUpdate, Position, Velocity);
   
      /* Register tags (components without a size) */
      ECS_TAG(world, Eats);
      ECS_TAG(world, Apples);
      ECS_TAG(world, Pears);
   
      /* Create an entity with name Bob, add Position and food preference */
      ecs_entity_t Bob = ecs_entity(world, { .name = "Bob" });
      ecs_set(world, Bob, Position, {0, 0});
      ecs_set(world, Bob, Velocity, {1, 2});
      ecs_add_pair(world, Bob, Eats, Apples);
   
      /* Run systems twice. Usually this function is called once per frame */
      ecs_progress(world, 0);
      ecs_progress(world, 0);
   
      /* See if Bob has moved (he has) */
      const Position *p = ecs_get(world, Bob, Position);
      printf("Bob's position is {%f, %f}\n", p->x, p->y);
   
      return ecs_fini(world);
   
      // Output
      //  Move entities with [Position, Velocity, (Identifier,Name), (Eats,Apples)]
      //  Move entities with [Position, Velocity, (Identifier,Name), (Eats,Apples)]
      //  Bob's position is {2.000000, 4.000000}
  }

• C++

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  #include <hello_world.h>
  #include <iostream>
   
  // Component types
  struct Position {
      double x;
      double y;
  };
   
  struct Velocity {
      double x;
      double y;
  };
   
  // Tag types
  struct Eats { };
  struct Apples { };
   
  int main(int, char *[]) {
      // Create the world
      flecs::world ecs;
   
      // Register system
      ecs.system<Position, Velocity>()
          .each([](Position& p, Velocity& v) {
              p.x += v.x;
              p.y += v.y;
          });
   
      // Create an entity with name Bob, add Position and food preference
      flecs::entity Bob = ecs.entity("Bob")
          .set(Position{0, 0})
          .set(Velocity{1, 2})
          .add<Eats, Apples>();
   
      // Show us what you got
      std::cout << Bob.name() << "'s got [" << Bob.type().str() << "]\n";
   
      // Run systems twice. Usually this function is called once per frame
      ecs.progress();
      ecs.progress();
   
      // See if Bob has moved (he has)
      const Position& p = Bob.get<Position>();
      std::cout << Bob.name() << "'s position is {" << p.x << ", " << p.y << "}\n";
   
      // Output
      //  Bob's got [Position, Velocity, (Identifier,Name), (Eats,Apples)]
      //  Bob's position is {2, 4}
  }