Question

我真的无法弄清楚这里发生了什么。

我有一个计算着色器，它接收FFT结果（来自实际输入）并计算每个bin的功率，将它们存储在不同的缓冲区（UAV）中。 FFT实现是D3DCSX库的实现。

有问题的着色器：

struct Complex {
    float real;
    float imag;
};

RWStructuredBuffer<Complex> g_result : register(u0);
RWStructuredBuffer<float> g_powers : register(u1);

[numthreads(1, 1, 1)] void main(uint3 id : SV_DispatchThreadID) {
    const uint  bin  = id.x;
    const float real = g_result[bin + 1].real;
    const float imag = g_result[bin + 1].imag;

    const float power = real * real + imag * imag;
    const float mag = sqrt(power);
    const float db = 10.0f * log10(1.0f + power);

    g_powers[bin] = power;
}

缓冲区创建代码：

//The buffer in which the resulting powers are stored (m_result_buffer1)
buffer_desc.BindFlags = D3D11_BIND_UNORDERED_ACCESS | D3D11_BIND_SHADER_RESOURCE;
buffer_desc.ByteWidth = sizeof(float) * NumBins();
buffer_desc.CPUAccessFlags = 0;
buffer_desc.MiscFlags = D3D11_RESOURCE_MISC_BUFFER_ALLOW_RAW_VIEWS;
buffer_desc.StructureByteStride = sizeof(float);
buffer_desc.Usage = D3D11_USAGE_DEFAULT;

hr = m_device->CreateBuffer (
    &buffer_desc,
    nullptr,
    &m_result_buffer1
); HR_THROW();

//UAV for m_result_buffer1
view_desc.ViewDimension = D3D11_UAV_DIMENSION_BUFFER;
view_desc.Buffer.FirstElement = 0;
view_desc.Format = DXGI_FORMAT_R32_TYPELESS;
view_desc.Buffer.Flags = D3D11_BUFFER_UAV_FLAG_RAW;
view_desc.Buffer.NumElements = NumBins();

hr = m_device->CreateUnorderedAccessView (
    m_result_buffer1,
    &view_desc,
    &m_result_view
); HR_THROW();

//Buffer for reading powers to the CPU
buffer_desc.BindFlags = 0;
buffer_desc.ByteWidth = sizeof(float) * NumBins();
buffer_desc.CPUAccessFlags = D3D11_CPU_ACCESS_READ;
buffer_desc.MiscFlags = 0;
buffer_desc.StructureByteStride = sizeof(float);
buffer_desc.Usage = D3D11_USAGE_STAGING;

hr = m_device->CreateBuffer (
    &buffer_desc,
    nullptr,
    &m_result_buffer2
); HR_THROW();

调度代码：

CComPtr<ID3D11UnorderedAccessView> result_view;

hr = m_fft->ForwardTransform (
    m_sample_view,
    &result_view
); HR_THROW();

ID3D11UnorderedAccessView* views[] = {
    result_view,  //FFT UAV   (u0)
    m_result_view //Power UAV (u1)
};

m_context->CSSetShader(m_power_cs, nullptr, 0);
m_context->CSSetUnorderedAccessViews(0, 2, views, nullptr);
m_context->Dispatch(NumBins(), 1, 1);

最后是CPU映射代码：

m_context->CopyResource(m_result_buffer2, m_result_buffer1);

D3D11_MAPPED_SUBRESOURCE sub = { 0 };

m_context->Map(m_result_buffer2, 0, D3D11_MAP_READ, 0, &sub);
memcpy(result, sub.pData, sizeof(float) * NumBins());
m_context->Unmap(m_result_buffer2, 0);

这个着色器似乎让每个线程都写入输出缓冲区中的相同索引。映射的缓冲区始终为第一个bin读取正确的值，然后为每个其他bin读取0.0f。 CPU上的等效代码运行得很好。奇怪的是，我已经放置了条件并且知道bin不仅仅是0，并且bin 0之外的每个bin的功率也不总是0.0f。我也尝试使用for循环在同一个线程上写入多个bin，同样的事情发生了。我做错了什么？

我有一种预感，它是问题根源的缓冲区创建代码或映射代码。我知道我在GPU上运行了正确数量的线程并且调度ID是正确的，这是CPU端错误的结果。

Answer 1

解决了问题！

我使用RWStructuredBuffer代表RWByteOrderBuffer。不完全确定这是如何导致这一结果的，但确实如此。因此，FFT结果现在为RWByteOrderBuffer。然而，这个缓冲区的奇怪之处在于D3DCSX实现将浮点值隔开太远 - 可能是出于缓存原因，但我老实说不太清楚为什么。这是我的计算着色器（这次计算分贝而不是功率 - 一个无关的变化）：

RWByteAddressBuffer       g_result   : register(u0);
RWStructuredBuffer<float> g_decibels : register(u1);

[numthreads(256, 1, 1)] void main(uint3 id : SV_DispatchThreadID) {
    const float real = asfloat(g_result.Load(id.x * 8 + 0));
    const float imag = asfloat(g_result.Load(id.x * 8 + 4));

    const float power = real * real + imag * imag;
    const float db = 10.0f * log10(1.0f + power);

    g_decibels[id.x] = db;
}

我将分贝缓冲区的描述更改为结构化缓冲区的描述，只是为了让我更容易：

buffer_desc.BindFlags = D3D11_BIND_UNORDERED_ACCESS | D3D11_BIND_SHADER_RESOURCE;
buffer_desc.ByteWidth = sizeof(float) * NumBins();
buffer_desc.CPUAccessFlags = 0;
buffer_desc.MiscFlags = D3D11_RESOURCE_MISC_BUFFER_STRUCTURED;
buffer_desc.StructureByteStride = sizeof(float);
buffer_desc.Usage = D3D11_USAGE_DEFAULT;

hr = m_device->CreateBuffer (
    &buffer_desc,
    nullptr,
    &m_result_buffer1
); HR_THROW();

view_desc.Buffer.FirstElement = 0;
view_desc.Buffer.Flags = 0;
view_desc.Buffer.NumElements = NumBins();
view_desc.Format = DXGI_FORMAT_UNKNOWN;
view_desc.ViewDimension = D3D11_UAV_DIMENSION_BUFFER;

hr = m_device->CreateUnorderedAccessView (
    m_result_buffer1,
    &view_desc,
    &m_result_view
); HR_THROW();

这就是g_decibels仍为RWStructuredBuffer。

的原因

我还不知道，只有在需要访问时，结果缓冲区是否可读/写是否重要 - 如果我将g_result更改为常规ByteOrderBuffer，则无法输出。但至少它现在正在工作。

DX11 Compute Shader仅写入一个索引

1 个答案: