systems/run_to_each_callback

• C++

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  #include <run_to_each_callback.h>
  #include <iostream>
   
  // This example shows how a system that uses the run callback can forward to an
  // each callback. This is often useful for installing generic behavior (like 
  // profiling, tracing) that wraps around the each callback.
   
  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>() 
          // Forward each result from the run callback to the each callback.
          .run([](flecs::iter& it) {
              std::cout << "Move begin\n";
   
              // Walk over the iterator, forward to the system callback
              while (it.next()) {
                  it.each();
              }
   
              std::cout << "Move end\n";
          },
          [](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();
   
      // Output
      //  Move begin
      //  e1: {11, 22}
      //  e2: {13, 24}
      //  Move end
  }