queries/iter_info

• C++

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  #include <iter_info.h>
  #include <iostream>
   
  struct Position { 
      double x, y;
  };
   
  struct Velocity { 
      double x, y;
  };
   
  struct Mass {
      double value;
  };
   
  int main(int, char *[]) {
      flecs::world ecs;
   
      // Create a query for Position, Velocity.
      flecs::query<Position, const Velocity> q = 
          ecs.query<Position, const Velocity>();
   
      // 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});
   
      ecs.entity("e3")
          .set<Position>({10, 20})
          .set<Velocity>({4, 5})
          .set<Mass>({50});
   
      // The run() function provides a flecs::iter object which contains all sorts
      // of information on the entities currently being iterated.
      q.run([&](flecs::iter& it) {
          while (it.next()) {
              auto p = it.field<Position>(0);
              auto v = it.field<const Velocity>(1);
   
              // Print the table & number of entities matched in current callback
              std::cout << "Table [" << it.type().str() << "]" << std::endl;
              std::cout << " - number of entities: " << it.count() << std::endl;
   
              // Print information about the components being matched
              for (int8_t i = 0; i < it.field_count(); i ++) {
                  std::cout << " - term " << i << ": " << std::endl;
                  std::cout << "   - component: " << it.id(i).str() << std::endl;
                  std::cout << "   - type size: " << it.size(i) << std::endl;
              }
   
              std::cout << std::endl;
   
              // Iterate entities
              for (auto i : it) {
                  p[i].x += v[i].x;
                  p[i].y += v[i].y;
                  std::cout << " - " << it.entity(i).name() << 
                      ": {" << p[i].x << ", " << p[i].y << "}\n";
              }
   
              std::cout << std::endl;
          }
      });
  }