Unity Optimized Transforms

An alternative LocalToWorld updater for Unity Entities, aimed at large, wide transform hierarchies. It groups children by depth and processes chunks in parallel within each level, so work under a single large root can spread across worker threads.

Enabled hierarchies update every frame with change checks. Disabled children update one depth slot per frame over a nine-frame cycle. Levels 1-8 use chunk jobs; deeper descendants use recursive traversal. Depth tags are maintained when parents change.

Use

Copy OptimizedTransforms.cs and Examples/DynamicLinkedEntityGroupSystem.cs into your project. The systems register automatically and disable Unity's built-in LocalToWorldSystem in their world. With a custom bootstrap, include the normal transform systems and these systems in the simulation world.

The implementation is shared unchanged. The example supplies its hierarchy-change tag and cleanup; it does not maintain linked entity groups or detect reparenting for you. If you already have that type, keep your own implementation instead of copying the example.

Used with Unity 6000.3.11f1 and these packages:

Package	Version
Entities	1.4.8
Unity Physics	1.4.7
Burst	1.8.30
Collections	2.6.8
Mathematics	1.3.3

Unity Physics is required by the PhysicsGraphicalSmoothing exclusion. For a custom assembly, reference Unity.Entities, Unity.Transforms, Unity.Physics, Unity.Burst, Unity.Collections and Unity.Mathematics, and enable unsafe code for generated Entities code. Other versions have not been checked.

Refreshing a disabled hierarchy

A disabled hierarchy can carry stale LocalToWorld values between its scheduled updates. To refresh it on the next transform update, add DynamicLinkedEntityGroupSystem.HierarchyChanged to its root, which must have Disabled, LocalTransform and LocalToWorld.

For example, when reparenting between two disabled hierarchies:

ecb.SetComponent(child, new Parent { Value = newParent });
ecb.AddComponent<DynamicLinkedEntityGroupSystem.HierarchyChanged>(oldRoot);
ecb.AddComponent<DynamicLinkedEntityGroupSystem.HierarchyChanged>(newRoot);

Play back those commands before TransformSystemGroup so ParentSystem updates the child buffers first. Read the rebuilt matrices after the transform group, observing normal job dependencies. The example schedules tag removal after that group and plays it back at the end of simulation. Ordinary movement needs no tag if delayed updates are acceptable.

Current limitations

• RequireForUpdate<Child>() needs at least one entity without Disabled carrying a Child buffer somewhere in the world. When that condition is met, the updater also handles standalone roots and disabled hierarchies. If no such entity exists after the built-in updater has been disabled, this system skips its entire update.
• The queries currently declare LocalToWorld read-only when setting up FilterWriteGroup. Custom transform writers are therefore not reliably excluded and their results can be overwritten.
• Frequent reparenting adds structural work. Deep or mixed enabled/disabled hierarchies need particular care; depth-tag changes can take multiple frames to propagate.

The intended workload is large hierarchies with mostly stable parent relationships. Measure it with your own hierarchy sizes and update patterns; no comparative benchmark results are included.

License

MIT.