Allow System's to be added pre-created to the SystemManager.

2 files changed, 48 insertions, 4 deletions

diff --git a/README.md b/README.md
index db4f140..cd5fff6 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,8 @@ As an example, a physics system might need *position* and *mass* data, while a c
 
 ## Tutorial
 
+
+
 ### Entities
 
 Entities are simply 64-bit numeric identifiers with which components are associated. Entity IDs are allocated by the `EntityManager`. Components are then associated with the entity, and can be queried or retrieved directly.
@@ -168,6 +170,34 @@ events.subscribe<Collision>(debug_collisions);
 
 ### World (tying it all together)
 
+Managing systems, components and entities can be streamlined by subclassing `World`. It is not necessary, but it provides callbacks for configuring systems, initializing entities and the world, and so on.
+
+To use it, subclass `World` and implement `configure()`, `initialize()` and `update()`:
+
+```
+class GameWorld : public World {
+ protected:
+  void configure() {
+    system_manager.add<MovementSystem>();
+    system_manager.add<CollisionSystem>();
+  }
+  
+  void initialize() {
+    // Create some entities in random locations heading in random directions
+    for (int i = 0; i < 100; ++i) {
+      Entity entity = entity_manager.create();
+      entity_manager.assign<Position>(entity, rand() % 100, rand() % 100);
+      entity_manager.assign<Direction>(entity, (rand() % 10) - 5, (rand() % 10) - 5);
+    }
+  }
+  
+  void update(double dt) {
+    system_manager.update<MovementSystem>(dt);
+    system_manager.update<CollisionSystem>(dt);
+  }
+};
+```
+
 ## Installation
 
 EntityX has the following build and runtime requirements:
@@ -184,4 +214,4 @@ Once these dependencies are installed you should be able to build and install En
 mkdir build && cd build && cmake .. && make && make test && make install
 ```
 
-EntityX has currently only been tested on Mac OSX (Lion and Mountain Lion). Reports and patches for builds on other platforms are welcome.
\ No newline at end of file
+EntityX has currently only been tested on Mac OSX (Lion and Mountain Lion). Reports and patches for builds on other platforms are welcome.
diff --git a/entityx/System.h b/entityx/System.h
index 1881b13..a754352 100644
--- a/entityx/System.h
+++ b/entityx/System.h
@@ -83,12 +83,26 @@ class SystemManager : boost::noncopyable {
    * Must be called before Systems can be used.
    *
    * eg.
-   * auto movement = system.add<MovementSystem>()
+   * boost::shared_ptr<MovementSystem> movement = boost::make_shared<MovementSystem>();
+   * system.add(movement);
+   */
+  template <typename S>
+  void add(boost::shared_ptr<S> system) {
+    systems_.insert(std::make_pair(S::family(), system));
+  }
+
+  /**
+   * Add a System to the SystemManager.
+   *
+   * Must be called before Systems can be used.
+   *
+   * eg.
+   * auto movement = system.add<MovementSystem>();
    */
   template <typename S, typename ... Args>
   boost::shared_ptr<S> add(Args && ... args) {
-    boost::shared_ptr<S> s(new S(args ...));
-    systems_.insert(std::make_pair(S::family(), s));
+    boost::shared_ptr<S> s = boost::make_shared<S>(args ...);
+    add(s);
     return s;
   }