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Martin Perry

DX11 [DX11] Update StructuredBuffer

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I have (RW)StructuredBuffer initialized to eg. 50MB. In each frame I need to fill it with different data in interval <10, 50> MB

If i use

deviceContext->UpdateSubresource( gpuBuffer->buffer, 0, NULL, data, 0, 0 );


works fine untill data has size 50MB

But if data are smaller, application crash on this line, no DX debug output nothing.

So i used for smaller data D3D11_BOX and fill it this way:

D3D11_BOX destRegion;
destRegion.left = 0;
destRegion.right = dataSize;
destRegion.top = 0;
destRegion.bottom = 1;
destRegion.front = 0;
destRegion.back = 1;

deviceContext->UpdateSubresource( gpuBuffer->buffer, 0, &destRegion, data, 0, 0 );

I hoped that data will be filled from index 0 - dataSize... BUT ...application doesn´t crash this time, however buffer has incorrect content... I got "blank" results if i vizualize content of buffer.

MSDN says nothing about D3D11_BOX and StructuredBuffers, so i really don´t know how to solve this.

Thank you for all answers

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That sounds like a pointer error to me. Are you sure you aren't exceeding the size of the buffer???

Also, you could try to use mapping instead of update subresource and see if you meet a similar issue. That would indicate that there is a general problem with the overall setup, or if it works then it would mean that you have an issue with update subresource.

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Size of buffer is not exceeded, its always smaller or same size as inited

I habe tried Map / Unmap, but it requires
CPUAccessFlags = D3D11_CPU_ACCESS_WRITE
which failed for StructuredBuffer with UAV | SRV

I inited buffer this way.

D3D11_BUFFER_DESC bufferDesc;


bufferDesc.BindFlags = D3D11_BIND_UNORDERED_ACCESS | D3D11_BIND_SHADER_RESOURCE;
bufferDesc.CPUAccessFlags = 0;
bufferDesc.MiscFlags = D3D11_RESOURCE_MISC_BUFFER_STRUCTURED;
bufferDesc.ByteWidth = gpuBuffer.elementSize * elementsCount;
bufferDesc.StructureByteStride = gpuBuffer.elementSize;
bufferDesc.Usage = D3D11_USAGE_DEFAULT;

// Create the constant buffer pointer so we can access the shader constant buffer from within this class.
HRESULT hr = this->device->CreateBuffer(&bufferDesc, NULL, &gpuBuffer.buffer);
if (FAILED(hr))
{
MyUtils::Logger::LogError("Failed to create buffer %s", bufferName.GetConstString());
return;
}

Than I init SRV and UAV for it

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In that case you will need to use two buffers - one with staging usage and the other one as you have already created. Then you write to the staging buffer, and then use copy resource to put the info into the default usage buffer.

It isn't ideal to do this copying, but from experience it is pretty fast since both resources are already on the GPU. In any case, you are only trying to isolate the problem, so this might still be helpful.

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I have found bug...

If filled data are from array, it crashed
If filled data are stored in vector and filled like &data[0], it works....

But I dont quite understand this behaviour. blink.png

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That would indicate that it was an issue with the array size - at least I think so anyways... At least you have a working solution now.

Did you try checking your vector size during runtime and ensure that it is in fact smaller than your array?

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I changed data representation from uint8 array to int array (inside shader i work with int buffer, uin8 representation was in byte form) and now it works fine..

Thank you

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