Why there is no DidChange method in BufferFromEntity<T>?

I see ComponentDataFromEntity<T> has DidChange() but BufferFromEntity<T> doesn't. Does anybody know a specific reason for this? Also I noticed that ArchetypeChunk has DidChange<T>() will happily accept T derived from IBufferElementData, but this doesn't help in the situations where I have to use BufferFromEntity, i.e. where I am reaching to another entity's buffer.
Any advice on how I can change-check dynamic buffers?

 

For those interested, this has been addressed in v.0.12.0, thank you @cort_of_unity!

 

Just noticed something - even though DidChange() was added to dynamic buffers, WithChangeFilter() still doesn't work properly with dynamic buffers, in my case it basically reports as always changed

 

If I'm not mistaken, that's because getting a buffer (even in ReadOnly) always marks it as a Read/Write. Not sure if it's a bug or a technical limitation I don't understand.

I modified the Entities package for one of my projects and added a true GetBufferReadOnly method. It seems to work fine at the moment.

 

Thank you @msfredb7. Can you share the code for the true read only buffer access method?

 

From the Git diff, I think that's all the changes related to my GetReadOnlyBuffer:

NB:
- My changes were done based on Entities 0.10.0, so they might not work out of the box for higher versions.
- This might very well expose bugs as I haven't tested all use cases
- Remember that this is not code officially supported by Unity. I suggest you rely on it as little as possible.

Unity.Entities/EntityManagerAccessComponentData.cs, line 305

Code (CSharp):

1. // ADDED BY FBESSETTE 2020-04-09
2. public DynamicBuffer<T> GetBufferReadOnly<T>(Entity entity) where T : struct, IBufferElementData
3. {
4.     var typeIndex = TypeManager.GetTypeIndex<T>();
5.     var ecs = GetCheckedReadEntityDataAccess();
6.  
7. #if ENABLE_UNITY_COLLECTIONS_CHECKS
8.     var safetyHandles = &ecs->DependencyManager->Safety;
9. #endif
10.  
11.     return ecs->GetBufferReadOnly<T>(entity
12. #if ENABLE_UNITY_COLLECTIONS_CHECKS
13.         , safetyHandles->GetSafetyHandle(typeIndex, true),
14.         safetyHandles->GetBufferSafetyHandle(typeIndex)
15. #endif
16.     );
17. }
18.  

Unity.Entities/EntityManager.cs, line 73

Code (CSharp):

1. // ADDED BY FBESSETTE 2020-05-24
2. internal EntityDataAccess* GetCheckedReadEntityDataAccess()
3. {
4. #if ENABLE_UNITY_COLLECTIONS_CHECKS
5.     AtomicSafetyHandle.CheckReadAndThrow(m_Safety);
6.     if (m_JobMode != m_EntityDataAccess->m_JobMode)
7.     {
8.         throw new InvalidOperationException($"EntityManager cannot be used from this context job mode {m_JobMode} != current mode {m_EntityDataAccess->m_JobMode}");
9.     }
10. #endif
11.     return m_EntityDataAccess;
12. }

Unity.Entities/ExclusiveEntityTransaction.cs, line 133

Code (CSharp):

1. // added by fbessette 2020-04-19
2. public DynamicBuffer<T> GetBufferReadOnly<T>(Entity entity) where T : struct, IBufferElementData
3. {
4.     return m_Manager.GetBufferReadOnly<T>(entity);
5. }

Unity.Entities/EntityDataAccess.cs, line 877

Code (CSharp):

1. // ADDED BY FBESSETTE 2020-04-19
2. public DynamicBuffer<T> GetBufferReadOnly<T>(Entity entity
3. #if ENABLE_UNITY_COLLECTIONS_CHECKS
4.     , AtomicSafetyHandle safety, AtomicSafetyHandle arrayInvalidationSafety
5. #endif
6.     ) where T : struct, IBufferElementData
7. {
8.     var typeIndex = TypeManager.GetTypeIndex<T>();
9.  
10. #if ENABLE_UNITY_COLLECTIONS_CHECKS
11.     EntityComponentStore->AssertEntityHasComponent(entity, typeIndex);
12.     if (!TypeManager.IsBuffer(typeIndex))
13.         throw new ArgumentException(
14.             $"GetBuffer<{typeof(T)}> may not be IComponentData or ISharedComponentData; currently {TypeManager.GetTypeInfo<T>().Category}");
15. #endif
16.  
17.     if (IsMainThread)
18.         DependencyManager->CompleteReadAndWriteDependency(typeIndex);
19.  
20.     BufferHeader* header =
21.             (BufferHeader*)EntityComponentStore->GetComponentDataWithTypeRO(entity, typeIndex);
22.  
23.     int internalCapacity = TypeManager.GetTypeInfo(typeIndex).BufferCapacity;
24.  
25. #if ENABLE_UNITY_COLLECTIONS_CHECKS
26.     var useMemoryInit = EntityComponentStore->useMemoryInitPattern != 0;
27.     byte memoryInitPattern = EntityComponentStore->memoryInitPattern;
28.     return new DynamicBuffer<T>(header, safety, arrayInvalidationSafety, true, useMemoryInit, memoryInitPattern, internalCapacity);
29. #else
30.     return new DynamicBuffer<T>(header, internalCapacity);
31. #endif
32. }

 

Thanks @msfredb7. I do realize this is not officially maintained code, I'm just stuck with my dynamic buffers constantly becoming overwritten (without this actually happening). In my case this leads to meshes being rebuilt every frame