Resolved PredictedPhysicsValidationSystem make an error debug

Thanks for the report hxh, please file it as a Unity bug report for tracking purposes (and link back to this thread).

 

The error is actually correct. We don't support that by default right now. PhysicsVelocity is not replicated for child entities (this is the current default setup). Nor their transform or other components (again this is the default).
So if you are using this pattern, be aware that the child entity state may be not synched to the client, unless you modify the variant to use for this child entity.

Also worth noticing: Physics objects are kinda special in general. Even if they are child in a hierarchy or prefab, they are disconnected by that hierarchy at runtime. They have no parent, and they are always root objects (in terms of transform).
Transform is in fact not synched either, you need to have joint or do that manually in case you need.

That being said, it you setup the replication for that child, so it work as expected, and that error is annoying or blocking you, it can be easily removed by changing the query builder at line 169 in PredictedPhysicsSystemGroup.cs

Code (csharp):

1.  
2. var builder = new EntityQueryBuilder(Allocator.Temp)
3. .WithAll<PhysicsVelocity, PhysicsWorldIndex>()
4. .WithAbsent<GhostInstance, GhostChildEntity>();
5.  

However, this is the fundamental fact, changing this check, without having another way to verify that the behaviour and replication configuration of the child ghost entity has been setup correctly can lead to errors or replication issue that at first glance may be harder to understand.

NOTE 2: The NetcodePhysicsRateManager requires that at least one physic entity with a PredictedGhostComponent exist at the moment. While that may be not a problem (you have other root ghosts with physics), in general, with child, that may be not sufficient to make replicated physics run.