How to build fast hierarchies for game objects using data oriented design

4 hours ago

ECS with integrated hierarchies is becoming common in libraries like Flecs, Unreal Mass, Bevy, Jecs, and BitECS.
Hierarchies should be part of the core ECS model, as relationships are fundamental in data models like relational databases.
Usability requires support for both asset hierarchies (for design) and scene hierarchies (for runtime).
Performance optimization uses data-oriented design, including arrays of structures (AoS) and structure of arrays (SoA).
Asset hierarchies in Flecs use prefabs with inheritance for variations and instancing, enabling runtime creation and overrides.
Fragmenting relationships (like IsA and ChildOf) group entities by archetype, improving performance for queries and rendering.
Component sharing reduces memory usage and improves cache efficiency by deduplicating data, with per-instance overrides.
Scene hierarchies face challenges with fragmenting (too many archetypes) vs. non-fragmenting (O(n) operations) approaches.
Flecs uses a hybrid hierarchy: fragmenting for small hierarchies and non-fragmenting for large ones, optimizing performance.
Examples show significant performance gains: from 10 FPS to 60 FPS in traffic scenes, and from 23 FPS to 90 FPS in city scenes.

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