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	ECS core components for entity lifecycle and relationships. More...

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 # helios::ecs::components

 

 ECS core components for entity lifecycle and relationships.

 

 ## Overview

 

 This submodule provides fundamental components used by the ECS architecture

 itself, as opposed to game-specific components defined in mechanics or modules.

 It includes tag components for entity activation state as well as hierarchy

 management for parent-child entity graphs.

 

 ## Components

 

 | Component | Purpose |

 |-----------|---------|

 | `Active` | Tag component marking an entity as active |

 | `Inactive` | Tag component marking an entity as inactive |

 | `HierarchyComponent` | Parent-child relationships for entity graphs |

 

 ## Active / Inactive

 

 Empty tag structs used to filter entities by activation state in views.

 Managed automatically by `Entity::setActive()`:

 

 - `setActive(true)` → adds `Active`, removes `Inactive`, calls `onActivate()`

 - `setActive(false)` → adds `Inactive`, removes `Active`, calls `onDeactivate()`

 

 ```cpp

 // Query only active entities

 for (auto [entity, health, active] : gameWorld->view<

  HealthComponent, Active

 >().whereEnabled()) { ... }

 ```

 

 ## HierarchyComponent

 

 Enables entities to form tree structures where state changes propagate from parent to child entities.

 

 **Members:**

 - `children_` – Child entity handles

 - `parent_` – Optional parent handle

 - `isDirty_` – Signals pending hierarchy propagation

 

 **Usage:**

 ```cpp

 auto* hc = entity.add<HierarchyComponent>();

 hc->setParent(parentHandle);

 hc->addChild(childHandle);

 hc->markDirty(); // Triggers propagation next frame

 ```

 

 ## Related Modules

 

 | Module | Purpose |

 |--------|---------|

 | `helios.ecs.Entity` | Manages `Active`/`Inactive` tags via `setActive()` |

 | `helios.ecs.systems` | Systems that process ECS components |

 

 ---

 <details>

 <summary>Doxygen</summary><p>

 @namespace helios::ecs::components

 @brief ECS core components for entity lifecycle and relationships.

 @details Provides tag components for entity activation state (Active, Inactive) and hierarchy management for parent-child entity relationships.

 </p></details>

 

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