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Diffstat (limited to 'README.md')
| -rw-r--r-- | README.md | 37 |
1 files changed, 27 insertions, 10 deletions
@@ -29,13 +29,15 @@ Entity entity = entities.create(); And destroying an entity is done with: ```c++ -entities.destroy(entity); +entity.destroy(); ``` -#### Testing for destroyed entities +#### Implementation details -The Entity type can be seen as a safe pointer. -Test if it is valid with `entity.exists()`. +- Each Entity is a convenience class wrapping an Entity::Id. +- An Entity handle can be invalidated with `invalidate()`. This does not affect the underlying entity. +- When an entity is destroyed the manager adds its ID to a free list and invalidates the Entity handle. +- When an entity is created IDs are recycled from the free list before allocating new ones. ### Components (entity data) @@ -43,11 +45,6 @@ The idea with ECS is to not have any functionality in the component. All logic s To that end Components are typically [POD types](http://en.wikipedia.org/wiki/Plain_Old_Data_Structures) containing self-contained sets of related data. Implementations are [curiously recurring template pattern](http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern) (CRTP) subclasses of `Component<T>`. -Implementation notes: - -- Components must provide a no-argument constructor. -- The current implementation can handle up to 64 components in total. - #### Creating components As an example, position and direction information might be represented as: @@ -103,6 +100,11 @@ if (position) { } ``` +#### Implementation notes + +- Components must provide a no-argument constructor. +- The current implementation can handle up to 64 components in total. This can be extended with little effort. + ### Systems (implementing behavior) Systems implement behavior using one or more components. Implementations are subclasses of `System<T>` and *must* implement the `update()` method, as shown below. @@ -187,7 +189,22 @@ DebugCollisions debug_collisions; events.subscribe<Collision>(debug_collisions); ``` -There can be more than one subscriber for an event; each one will be called. +#### Builtin events + +Several events are emitted by EntityX itself: + +- `EntityCreatedEvent` - emitted when a new Entity has been created. + - `Entity entity` - Newly created Entity. +- `EntityDestroyedEvent` - emitted when an Entity is *about to be* destroyed. + - `Entity entity` - Entity about to be destroyed. +- `ComponentAddedEvent<T>` - emitted when a new component is added to an entity. + - `Entity entity` - Entity that component was added to. + - `boost::shared_ptr<T> component` - The component added. + +#### Implementation notes + +- There can be more than one subscriber for an event; each one will be called. +- Event objects are destroyed after delivery, so references should not be retained. ### Manager (tying it all together) |