systems/run_callback

• C

  View on GitHub

  #include <run_callback.h>
  #include <stdio.h>
   
  // Systems can be created with a custom run function that takes control over the
  // entire iteration. By default, a system is invoked once per matched table, 
  // which means the function can be called multiple times per frame. In some
  // cases that's inconvenient, like when a system has things it needs to do only
  // once per frame. For these use cases, the run callback can be used which is
  // called once per frame per system.
   
  typedef struct {
      double x, y;
  } Position, Velocity;
   
  void Move(ecs_iter_t *it) {
      printf("Move begin\n");
   
      // In a run function we have to manually iterate through the query results.
      // Note that this code looks the same as iterating a query.
      while (ecs_query_next(it)) {
          // Inside the loop the code looks the same as for a regular system
          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);
          }
      }
   
      printf("Move end\n");
  }
   
  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, {
          .query.terms = {
              { .id = ecs_id(Position) },
              { .id = ecs_id(Velocity), .inout = EcsIn }
          },
          .run = Move // use .run instead of .callback
      });
   
      // 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);
   
      // Output
      //  Move begin
      //  e1: {11.000000, 22.000000}
      //  e2: {13.000000, 24.000000}
      //  Move end
  }

• C++

  View on GitHub

  #include <run_callback.h>
  #include <iostream>
   
  // This example shows how to use the run callback, which provides more direct
  // control over the iteration of the system. It also makes it easier to run code
  // before and after the iteration.
   
  struct Position { 
      double x, y;
  };
   
  struct Velocity { 
      double x, y;
  };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      flecs::system s = ecs.system<Position, const Velocity>() 
          .run([](flecs::iter& it) {
              std::cout << "Move begin\n";
   
              while (it.next()) {
                  auto p = it.field<Position>(0);
                  auto v = it.field<const Velocity>(1);
   
                  for (auto i : it) {
                      flecs::entity e = it.entity(i);
                      p[i].x += v[i].x;
                      p[i].y += v[i].y;
                      std::cout << e.name() 
                                << ": {" << p[i].x << ", " << p[i].y << "}\n";
                  }
              }
   
              std::cout << "Move end\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();
   
      // Output
      //  Move begin
      //  e1: {11, 22}
      //  e2: {13, 24}
      //  Move end
  }