systems/basics

• C

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  #include <basics.h>
  #include <stdio.h>
   
  typedef struct {
      double x, y;
  } Position, Velocity;
   
  void Move(ecs_iter_t *it) {
      Position *p = ecs_field(it, Position, 0);
      const Velocity *v = ecs_field(it, Velocity, 1);
   
      for (int i = 0; i < it->count; i ++) {
          p[i].x += v[i].x;
          p[i].y += v[i].y;
          printf("%s: {%f, %f}\n", ecs_get_name(it->stage, it->entities[i]),
              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);
      ECS_COMPONENT(ecs, Velocity);
   
      // Create a system for Position, Velocity.
      ecs_entity_t move = ecs_system(ecs, {
          // Systems are entities, and by initializing the .entity field we can
          // set some additional properties for the system like a name. While this
          // is not mandatory, it makes a system easier to find in tools like the
          // explorer (https://www.flecs.dev/explorer/).
          .entity = ecs_entity(ecs, {
              .name = "Move" 
          }),
          .query.terms = {
              { .id = ecs_id(Position) },
              { .id = ecs_id(Velocity), .inout = EcsIn }
          },
          .callback = Move
      });
   
      // C applications can also use the ECS_SYSTEM convenience macro:
      // ECS_SYSTEM(ecs, Move, 0, Position, [in] Velocity);
   
      // Create a few test entities for a Position, Velocity query
      ecs_entity_t e1 = ecs_entity(ecs, { .name = "e1" });
      ecs_set(ecs, e1, Position, {10, 20});
      ecs_set(ecs, e1, Velocity, {1, 2});
   
      ecs_entity_t e2 = ecs_entity(ecs, { .name = "e2" });
      ecs_set(ecs, e2, Position, {10, 20});
      ecs_set(ecs, e2, Velocity, {3, 4});
   
      // This entity will not match as it does not have Position, Velocity
      ecs_entity_t e3 = ecs_entity(ecs, { .name = "e3" });
      ecs_set(ecs, e3, Position, {10, 20});
   
      // Run the system
      ecs_run(ecs, move, 0.0f, NULL);
   
      return ecs_fini(ecs);
  }

• C++

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  #include <systems.h>
  #include <iostream>
   
  struct Position { 
      double x, y;
  };
   
  struct Velocity { 
      double x, y;
  };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      // Create a system for Position, Velocity. Systems are like queries (see
      // queries) with a function that can be ran or scheduled (see pipeline).
      flecs::system s = ecs.system<Position, const Velocity>()
          .each([](flecs::entity e, Position& p, const Velocity& v) {
              p.x += v.x;
              p.y += v.y;
              std::cout << e.name() << ": {" << p.x << ", " << p.y << "}\n";
          });
   
      // Create a few test entities for a Position, Velocity query
      ecs.entity("e1")
          .set<Position>({10, 20})
          .set<Velocity>({1, 2});
   
      ecs.entity("e2")
          .set<Position>({10, 20})
          .set<Velocity>({3, 4});
   
      // This entity will not match as it does not have Position, Velocity
      ecs.entity("e3")
          .set<Position>({10, 20});
   
      // Run the system
      s.run();
  }