I'm trying to implement the 3rd exercise in chapter 12 of Introduction to 3D Game Programming with DirectX 11, that is:

• Implement a Compute Shader to calculate the length of 64 vectors.

Previous exercises ask you to do the same with typed buffers and regular structured buffers and I had no problems with them.

For what I've read, [Consume|Append]StructuredBuffers are bound to the pipeline using UnorderedAccessViews (as long as they use the D3D11_BUFFER_UAV_FLAG_APPEND, and the buffers have both D3D11_BIND_SHADER_RESOURCE and D3D11_BIND_UNORDERED_ACCESS bind flags).

Problem is: my AppendStructuredBuffer works, since I can append data to it and retrieve it from the application to write to a results file, but the ConsumeStructuredBuffer always returns zeroed data. Data is in the buffer, since if I change the UAV to a ShaderResourceView and to a StructuredBuffer in the HLSL side it works.

I don't know what I am missing:

• Should I initialize the ConsumeStructuredBuffer on the GPU, or can I do it when I create the buffer (as I amb currently doing).
• Is it OK to bind the buffer with a UAV as described above? Do I need to bind it as a ShaderResourceView somehow?
• Maybe I am missing some step?

This is the declaration of buffers in the Compute Shader:

struct Data
{
    float3 v;
};

struct Result
{
    float l;
};

ConsumeStructuredBuffer<Data> gInput;
AppendStructuredBuffer<Result> gOutput;

And here the creation of the buffer and UAV for input data:

D3D11_BUFFER_DESC inputDesc;
inputDesc.Usage = D3D11_USAGE_DEFAULT;
inputDesc.ByteWidth = sizeof(Data) * mNumElements;
inputDesc.BindFlags = D3D11_BIND_SHADER_RESOURCE | D3D11_BIND_UNORDERED_ACCESS;
inputDesc.CPUAccessFlags = 0;
inputDesc.StructureByteStride = sizeof(Data);
inputDesc.MiscFlags = D3D11_RESOURCE_MISC_BUFFER_STRUCTURED;

D3D11_SUBRESOURCE_DATA vinitData;
vinitData.pSysMem = &data[0];

HR(md3dDevice->CreateBuffer(&inputDesc, &vinitData, &mInputBuffer));

D3D11_UNORDERED_ACCESS_VIEW_DESC uavDesc;
uavDesc.Format = DXGI_FORMAT_UNKNOWN;
uavDesc.ViewDimension = D3D11_UAV_DIMENSION_BUFFER;
uavDesc.Buffer.FirstElement = 0;
uavDesc.Buffer.Flags = D3D11_BUFFER_UAV_FLAG_APPEND;
uavDesc.Buffer.NumElements = mNumElements;

md3dDevice->CreateUnorderedAccessView(mInputBuffer, &uavDesc, &mInputUAV);

Initial data is an array of Data structs, which contain a XMFLOAT3 with random data.

I bind the UAV to the shader using the Effects framework:

ID3DX11EffectUnorderedAccessViewVariable* Input = mFX->GetVariableByName("gInput")->AsUnorderedAccessView();

Input->SetUnorderedAccessView(uav); // uav is mInputUAV

Any ideas?

Thank you.