systems/sync_point

• C

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  #include <sync_point.h>
  #include <stdio.h>
   
  typedef struct {
      double x, y;
  } Position, Velocity;
   
  // Forward declare components so they can be accessed from systems
  ECS_COMPONENT_DECLARE(Position);
  ECS_COMPONENT_DECLARE(Velocity);
   
  void SetVelocity(ecs_iter_t *it) {
      for (int i = 0; i < it->count; i ++) {
          ecs_set(it->stage, it->entities[i], Velocity, {1, 2});
      }
  }
   
  void Move(ecs_iter_t *it) {
      Position *p = ecs_field(it, Position, 0);
      const Velocity *v = ecs_field(it, const Velocity, 1);
   
      for (int i = 0; i < it->count; i ++) {
          p[i].x += v[i].x;
          p[i].y += v[i].y;
      }
  }
   
  void PrintPosition(ecs_iter_t *it) {
      const Position *p = ecs_field(it, const Position, 0);
   
      for (int i = 0; i < it->count; i ++) {
          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_DEFINE(ecs, Position);
      ECS_COMPONENT_DEFINE(ecs, Velocity);
   
      // System that sets velocity using set<T> for entities with Position.
      // While systems are progressing, operations like set<T> are deferred until
      // it is safe to merge. By default this merge happens at the end of the
      // frame, but we can annotate systems to give the scheduler more information
      // about what it's doing, which allows it to insert sync points earlier.
      // 
      // The parentheses after Velocity indicate that the component is not used
      // to match entities, while [out] indicates that it is written. A subsequent
      // system that accesses the component will cause the scheduler to insert a
      // sync point.
      //
      // Note that sync points are never necessary/inserted for systems that write
      // components provided by their signature, as these writes directly happen
      // in the ECS storage and are never deferred.
      //
      // The [none] annotation for Position tells the scheduler that while we 
      // want to match entities with Position, we're not interested in reading or 
      // writing the component value.
      ECS_SYSTEM(ecs, SetVelocity, EcsOnUpdate, [none] Position, [out] Velocity());
   
      // This system reads Velocity, which causes the insertion of a sync point.
      ECS_SYSTEM(ecs, Move, EcsOnUpdate, Position, [in] Velocity);
   
      // Print resulting Position
      ECS_SYSTEM(ecs, PrintPosition, EcsPostUpdate, [in] Position);
   
      // 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});
   
      // Run systems. Debug logging enables us to see the generated schedule
      ecs_log_set_level(1);
      ecs_progress(ecs, 0.0f);
      ecs_log_set_level(-1); // Restore so we don't get world cleanup logs
   
      // Output:
      //  info: pipeline rebuild:
      //  info: | schedule: threading: 0, staging: 1:
      //  info: | | system SetVelocity
      //  info: | | merge
      //  info: | schedule: threading: 0, staging: 1:
      //  info: | | system Move
      //  info: | | system PrintPosition
      //  info: | | merge
      //  e1: {11.000000, 22.000000}
      //  e2: {11.000000, 22.000000}
      //
      // The "merge" lines indicate sync points.
      //
      // Removing the '[out] Velocity()' annotation from the system will remove
      // the first sync point from the schedule.
      //
      // To create the same system with ecs_system_init, do:
      //  ecs_system_init(ecs, &(ecs_system_desc_t){
      //      .query.terms = {
      //          { 
      //              .id = ecs_id(Position), 
      //              .inout = EcsInOutNone 
      //          },
      //          { 
      //              .id = ecs_id(Velocity), 
      //              .inout = EcsOut, 
      //              .src.id = EcsIsEntity 
      //          }
      //      },
      //      .entity = {
      //          .name = "SetVelocity"
      //      },
      //      .phase = EcsOnUpdate,
      //      .callback = SetVelocity
      //  });
   
      return ecs_fini(ecs);
  }

• C++

  View on GitHub

  #include <sync_point.h>
  #include <iostream>
   
  struct Position { 
      double x, y;
  };
   
  struct Velocity { 
      double x, y;
  };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      // System that sets velocity using ecs_set for entities with Position.
      // While systems are progressing, operations like ecs_set are deferred until
      // it is safe to merge. By default this merge happens at the end of the
      // frame, but we can annotate systems to give the scheduler more information
      // about what it's doing, which allows it to insert sync points earlier.
      //
      // Note that sync points are never necessary/inserted for systems that write
      // components provided by their signature, as these writes directly happen
      // in the ECS storage and are never deferred.
      //
      // .inout_none() for Position tells the scheduler that while we 
      // want to match entities with Position, we're not interested in reading or 
      // writing the component value.
      ecs.system("SetVelocity")
          .with<Position>().inout_none()
          .write<Velocity>() // Velocity is written, but shouldn't be matched
          .each([](flecs::entity e) {
              e.set<Velocity>({1, 2});
          });
   
      // This system reads Velocity, which causes the insertion of a sync point.
      ecs.system<Position, const Velocity>("Move")
          .each([](Position& p, const Velocity& v) {
              p.x += v.x;
              p.y += v.y;
          });
   
      // Print resulting Position
      ecs.system<const Position>("PrintPosition")
          .each([](flecs::entity e, const Position& p) {
              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});
   
      // Run systems. Debug logging enables us to see the generated schedule
      flecs::log::set_level(1);
      ecs.progress();
      flecs::log::set_level(-1); // Restore so we don't get world cleanup logs
   
      // Output:
      //  info: pipeline rebuild:
      //  info: | schedule: threading: 0, staging: 1:
      //  info: | | system SetVelocity
      //  info: | | merge
      //  info: | schedule: threading: 0, staging: 1:
      //  info: | | system Move
      //  info: | | system PrintPosition
      //  info: | | merge
      //  e1: {11.000000, 22.000000}
      //  e2: {11.000000, 22.000000}
      //
      // The "merge" lines indicate sync points.
      //
      // Removing '.write<Velocity>()' from the system will remove the first
      // sync point from the schedule.
  }