Converting a ComputeBuffer To a NativeArray

Hello everyone,

I am trying to use the ConvertExistingDataToNativeArray function, in order to pass the contents of a ComputeBuffer to a NativeArray<float>, avoiding the ComputeBuffer's GetData(T[]) function.

My function so far looks like this (performs some calculations on a RenderTexture via a Compute Shader, then gets the results back as a ComputeBuffer):

Code (CSharp):

1.  public unsafe void GetCellStates(ref ComputeBuffer buffer, ref NativeArray<float> array, in RenderTexture tex)
2.     {
3.         readBackShader.SetTexture(getPixelsKernel,"Input", tex);
4.         readBackShader.SetBuffer(getPixelsKernel, "Data", buffer);
5.         readBackShader.Dispatch(getPixelsKernel, CA3DScript.CountX/16, CA3DScript.CountY/8, CA3DScript.CountZ/8);
6.      
7.         array = ConvertExistingDataToNativeArray<float>( buffer.GetNativeBufferPtr().ToPointer(), CA3DScript.totalCount * 4, Allocator.Persistent);
8. }

The problem is that I get a Null Reference Exception every time I try to do something with the NativeArray afterwards ( Copying to another array, accessing elements, passing it to a Job), although it has a non-zero length and IsCreated = true.

NullReferenceException: Object reference not set to an instance of an object

Unity.Collections.LowLevel.Unsafe.AtomicSafetyHandle.CheckReadAndThrow (Unity.Collections.LowLevel.Unsafe.AtomicSafetyHandle handle) (at C:/buildslave/unity/build/Runtime/Export/Jobs/AtomicSafetyHandle.bindings.cs:147)

I don't have a good idea as to what might be wrong. Could some Pointer Wizard have a look ?

Thanks in advance!

 

After a
NativeArrayUnsafeUtility.ConvertExistingDataToNativeArray

you also need a
NativeArrayUnsafeUtility.SetAtomicSafetyHandle

 

@tertle I'm glad I get the chance thank you for your huge contribution to the forums!
Based on your suggestions in this thread i modified my code:

Code (CSharp):

1.    public unsafe void GetCellStates(out NativeArray<float> array)
2.     {
3.         array = ConvertExistingDataToNativeArray<float>( getPixelsBuffer.GetNativeBufferPtr().ToPointer(), CA3DScript.totalCount * 4, Allocator.Invalid);
4.  
5. #if ENABLE_UNITY_COLLECTIONS_CHECKS
6.         SetAtomicSafetyHandle(ref array, AtomicSafetyHandle.Create());
7. #endif
8.     }

However anytime I try to access the NativeArray outside the function that created it, ie in a Parallel Job (as [ReadOnly]), Unity throws a Null Reference exception:

NullReferenceException: Object reference not set to an instance of an object

Unity.Collections.LowLevel.Unsafe.UnsafeUtility.ReadArrayElement[T] (System.Void* source, System.Int32 index) (at C:/buildslave/unity/build/Runtime/Export/Unsafe/UnsafeUtilityPatched.cs:48)

Unity.Collections.NativeArray`1[T].get_Item (System.Int32 index) (at C:/buildslave/unity/build/Runtime/Export/NativeArray/NativeArray.cs:139)

CA3DInterface+AdditiveBlendJob.Execute (System.Int32 index) (at Assets/CA3DInterface.cs:265)

Unity.Jobs.IJobParallelForExtensions+ParallelForJobStruct`1[T].Execute (T& jobData, System.IntPtr additionalPtr, System.IntPtr bufferRangePatchData, Unity.Jobs.LowLevel.Unsafe.JobRanges& ranges, System.Int32 jobIndex) (at C:/buildslave/unity/build/Runtime/Jobs/Managed/IJobParallelFor.cs:43)

 

Just my 5 cents. New API got introduced with 2019.3 which allows to not just get a NativeArray<> with AsyncGPUReadback, but also fill a NativeArray of your choice with "AsyncGPUReadback.RequestIntoNativeArray(ref NativeArray_1, ComputeBuffer)". I haven't used it myself, but this should allow to fill arrays with any allocation directly.

 

Thanks a lot @richardkettlewell and @crysicle for your answers. I ended up scheduling a request with CommandBuffer.RequestAsyncReadbackIntoNativeArray and it works like a charm!

 

Hi,

@richardkettlewell I get the async stuff bu I don't get why there is a SetData<T>(NativeArray<T> data) but no corresponding GetData<T>(NativeArray<T> data)? Could you please clarify?

Thanks

 

ComputBuffer

 

That would be great, removing an unnecessary CopyTo() call.

 

Awesome !

 

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