helios/engine/ecs/systems/README.md File

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namespace	systems
	Core ECS systems for entity management. More...

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 # helios::engine::ecs::systems

 

 Core ECS systems for entity management and hierarchy propagation.

 

 ## Overview

 

 This submodule contains systems that operate on fundamental ECS components. These systems are typically registered early in the game loop to ensure proper entity state before game-specific systems run.

 

 ## Systems

 

 | System | Purpose |

 |--------|---------|

 | `HierarchyPropagationSystem` | Propagates activation state through entity hierarchies |

 

 ## HierarchyPropagationSystem

 

 Processes entities with `HierarchyComponent` and propagates their active/inactive state to all descendants.

 

 **Behavior:**

 

 1 Finds root entities (no parent) that are marked dirty

 2 For active roots: recursively activates all children

 3 For inactive roots: recursively deactivates all children

 4 Clears dirty flag after propagation

 

 **Required Components:**

 - `HierarchyComponent` – Hierarchy relationships

 - `Active` or `Inactive` – Lifecycle tag components

 

 **Usage:**

 ```cpp

 // Register in game loop

 systemRegistry.add<HierarchyPropagationSystem>(Phase::Pre);

 

 // When entity activation changes

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

 hc->markDirty(); // Children will be updated next frame

 ```

 

 ## Related Modules

 

 | Module | Purpose |

 |--------|---------|

 | `helios.engine.ecs.components` | Components processed by these systems |

 | `helios.engine.mechanics.lifecycle` | Active/Inactive components |

 

 ---

 <details>

 <summary>Doxygen</summary><p>

 @namespace helios::engine::ecs::systems

 @brief Core ECS systems for entity management.

 @details Provides systems that operate on fundamental ECS components, including hierarchy propagation for parent-child entity relationships.

 </p></details>

 

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