queries/group_by_callbacks

• C

  View on GitHub

  #include <group_by_callbacks.h>
  #include <stdio.h>
  #include <stdlib.h>
   
  // This example shows how the on_group_create and on_group_delete callbacks can
  // be used to get notified when a new group is registered for a query. These
  // callbacks make it possible to associate and manage user data attached to
  // groups.
   
  typedef struct {
      double x, y;
  } Position;
   
  // Custom type to associate with group
  typedef struct {
      int32_t counter;
  } group_ctx;
   
  int group_counter = 0;
   
  // Callback invoked when a new group is created
  static void* on_group_create(ecs_world_t *world, 
      uint64_t group_id,  // id of the group that was created
      void *group_by_arg) // group_by_ctx parameter in ecs_query_desc_t struct
  {
      (void)group_by_arg; // silence unused warning
      printf("Group %s created\n", ecs_get_name(world, group_id));
   
      // Return data that will be associated with the group
      group_ctx *ctx = malloc(sizeof(group_ctx));
      ctx->counter = ++ group_counter;
      return ctx;
  }
   
  // Callback invoked when a group is deleted
  static void on_group_delete(ecs_world_t *world, 
      uint64_t group_id,  // id of the group that was deleted
      void *ctx,          // group context
      void *group_by_arg) // group_by_ctx parameter in ecs_query_desc_t struct
  {
      (void)group_by_arg; // silence unused warning
      printf("Group %s deleted\n", ecs_get_name(world, group_id));
   
      // Free data associated with group
      free(ctx);
  }
   
  int main(int argc, char *argv[]) {
      ecs_world_t *ecs = ecs_init_w_args(argc, argv);
   
      ECS_COMPONENT(ecs, Position);
      ECS_TAG(ecs, Tag); // Dummy tag to put entities in different tables
   
      // Create a relationship to use for the group_by function. Tables will
      // be assigned the relationship target as group id
      ECS_TAG(ecs, Group);
   
      // Targets for the relationship, which will be used as group ids.
      ECS_TAG(ecs, First);
      ECS_TAG(ecs, Second);
      ECS_TAG(ecs, Third);
   
      // Grouped query
      ecs_query_t *q = ecs_query(ecs, {
          .terms = {
              { .id = ecs_id(Position) }
          },
          .group_by = Group,
          .on_group_create = on_group_create,
          .on_group_delete = on_group_delete
      });
   
      // Create entities in 6 different tables with 3 group ids
      ecs_entity_t e1 = ecs_new_w_pair(ecs, Group, Third);
      ecs_set(ecs, e1, Position, {1, 1});
   
      ecs_entity_t e2 = ecs_new_w_pair(ecs, Group, Second);
      ecs_set(ecs, e2, Position, {2, 2});
   
      ecs_entity_t e3 = ecs_new_w_pair(ecs, Group, First);
      ecs_set(ecs, e3, Position, {3, 3});
   
      ecs_entity_t e4 = ecs_new_w_pair(ecs, Group, Third);
      ecs_set(ecs, e4, Position, {4, 4});
      ecs_add(ecs, e4, Tag);
   
      ecs_entity_t e5 = ecs_new_w_pair(ecs, Group, Second);
      ecs_set(ecs, e5, Position, {5, 5});
      ecs_add(ecs, e5, Tag);
   
      ecs_entity_t e6 = ecs_new_w_pair(ecs, Group, First);
      ecs_set(ecs, e6, Position, {6, 6});
      ecs_add(ecs, e6, Tag);
   
      // The query cache now looks like this:
      //  - group First:
      //     - table [Position, (Group, First)]
      //     - table [Position, Tag, (Group, First)]
      //
      //  - group Second:
      //     - table [Position, (Group, Second)]
      //     - table [Position, Tag, (Group, Second)]
      //  
      //  - group Third:
      //     - table [Position, (Group, Third)]
      //     - table [Position, Tag, (Group, Third)]
      //
   
      printf("\n");
   
      // Iterate query, print position & table components
      ecs_iter_t it = ecs_query_iter(ecs, q);
      while (ecs_query_next(&it)) {
          Position *p = ecs_field(&it, Position, 0);
          char *table_str = ecs_table_str(ecs, it.table);
   
          uint64_t group_id = ecs_iter_get_group(&it);
          char *group_str = ecs_get_path(ecs, group_id);
          group_ctx *ctx = ecs_query_get_group_ctx(q, group_id);
   
          printf(" - group %s: table [%s]\n", group_str, table_str);
          printf("   counter: %d\n", ctx->counter);
   
          for (int i = 0; i < it.count; i ++) {
              printf("     {%f, %f}\n", p[i].x, p[i].y);
          }
   
          ecs_os_free(group_str);
          ecs_os_free(table_str);
          printf("\n");
      }
   
      // Deleting the query will call the on_group_deleted callback
      ecs_query_fini(q);
   
      // Output:
      //   Group Third created
      //   Group Second created
      //   Group First created
      //   
      //    - group First: table [Position, (Group,First)]
      //      counter: 3
      //        {3.000000, 3.000000}
      //   
      //    - group First: table [Position, Tag, (Group,First)]
      //      counter: 3
      //        {6.000000, 6.000000}
      //   
      //    - group Second: table [Position, (Group,Second)]
      //      counter: 2
      //        {2.000000, 2.000000}
      //   
      //    - group Second: table [Position, Tag, (Group,Second)]
      //      counter: 2
      //        {5.000000, 5.000000}
      //   
      //    - group Third: table [Position, (Group,Third)]
      //      counter: 1
      //        {1.000000, 1.000000}
      //   
      //    - group Third: table [Position, Tag, (Group,Third)]
      //      counter: 1
      //        {4.000000, 4.000000}
      //   
      //   Group First deleted
      //   Group Third deleted
      //   Group Second deleted
   
      return ecs_fini(ecs);
  }

• C++

  View on GitHub

  #include <group_by_callbacks.h>
  #include <iostream>
   
  // This example shows how the on_group_create and on_group_delete callbacks can
  // be used to get notified when a new group is registered for a query. These
  // callbacks make it possible to associate and manage user data attached to
  // groups.
   
  struct Position {
      double x, y;
  };
   
  // Custom type to associate with group
  struct group_ctx {
      int32_t counter;
  };
   
  int group_counter = 0;
   
  // Dummy tag to put entities in different tables
  struct Tag { };
   
  // Create a relationship to use for the group_by function. Tables will
  // be assigned the relationship target as group id
  struct Group { };
   
  // Targets for the relationship, which will be used as group ids.
  struct First { };
  struct Second { };
  struct Third { };
   
  int main() {
      flecs::world ecs;
   
      // Register components in order so that id for First is lower than Third
      ecs.component<First>();
      ecs.component<Second>();
      ecs.component<Third>();
   
      // Grouped query
      flecs::query<Position> q = ecs.query_builder<Position>()
          .group_by<Group>()
   
          // Callback invoked when a new group is created
          .on_group_create([](flecs::world_t *world, 
              uint64_t id,         // id of the group that was created
              void *group_by_arg)  // group_by_ctx parameter in ecs_query_desc_t struct
          {
              (void)group_by_arg; // silence unused warning
              flecs::world w(world);
              std::cout << "Group " << w.entity(id).name() << " created\n";
   
              // Return data that will be associated with the group
              group_ctx *ctx = new group_ctx;
              ctx->counter = ++ group_counter;
              return static_cast<void*>(ctx); // Cast to make sure function type matches
          })
   
          // Callback invoked when a group is deleted
          .on_group_delete([](flecs::world_t *world, 
              uint64_t id,         // id of the group that was deleted
              void *ctx,           // group context
              void *group_by_arg)  // group_by_ctx parameter in ecs_query_desc_t struct
          {
              (void)group_by_arg; // silence unused warning
              flecs::world w(world);
              std::cout << "Group " << w.entity(id).name() << " deleted\n";
   
              // Free data associated with group
              delete static_cast<group_ctx*>(ctx);
          })
          .build();
   
      // Create entities in 6 different tables with 3 group ids
      ecs.entity().add<Group, Third>()
          .set<Position>({1, 1});
      ecs.entity().add<Group, Second>()
          .set<Position>({2, 2});
      ecs.entity().add<Group, First>()
          .set<Position>({3, 3});
   
      ecs.entity().add<Group, Third>()
          .set<Position>({4, 4})
          .add<Tag>();
      ecs.entity().add<Group, Second>()
          .set<Position>({5, 5})
          .add<Tag>();
      ecs.entity().add<Group, First>()
          .set<Position>({6, 6})
          .add<Tag>();
   
      // The query cache now looks like this:
      //  - group First:
      //     - table [Position, (Group, First)]
      //     - table [Position, Tag, (Group, First)]
      //
      //  - group Second:
      //     - table [Position, (Group, Second)]
      //     - table [Position, Tag, (Group, Second)]
      //  
      //  - group Third:
      //     - table [Position, (Group, Third)]
      //     - table [Position, Tag, (Group, Third)]
      //
   
      std::cout << "\n";
   
      q.run([&](flecs::iter& it) {
          while (it.next()) {
              auto p = it.field<Position>(0);
   
              flecs::entity group = ecs.entity(it.group_id());
              group_ctx *ctx = static_cast<group_ctx*>(q.group_ctx(group));
   
              std::cout << " - group " << group.path() << ": "
                        << "table [" << it.table().str() << "]\n";
              std::cout << "   counter: " << ctx->counter << "\n";
   
              for (auto i : it) {
                  std::cout << "     {" << p[i].x << ", " << p[i].y << "}\n";
              }
   
              std::cout << "\n";
          }
      });
   
      // Deleting the query will call the on_group_deleted callback
      q.destruct();
   
      // Output:
      //  Group Third created
      //  Group Second created
      //  Group First created
      //  
      //   - group ::First: table [Position, (Group,First)]
      //     counter: 3
      //       {3, 3}
      //  
      //   - group ::First: table [Position, Tag, (Group,First)]
      //     counter: 3
      //       {6, 6}
      //  
      //   - group ::Second: table [Position, (Group,Second)]
      //     counter: 2
      //       {2, 2}
      //  
      //   - group ::Second: table [Position, Tag, (Group,Second)]
      //     counter: 2
      //       {5, 5}
      //  
      //   - group ::Third: table [Position, (Group,Third)]
      //     counter: 1
      //       {1, 1}
      //  
      //   - group ::Third: table [Position, Tag, (Group,Third)]
      //     counter: 1
      //       {4, 4}
      //  
      //  Group Third deleted
      //  Group Second deleted
      //  Group First deleted
  }