1

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（来自真实输入）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);

发生的情况是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。映射缓冲区总是为第一个 bin 读取正确的值，然后为每个其他 bin 读取 0.0f。CPU 上的等效代码运行良好。奇怪的是我已经放置了条件并且知道它bin不只是 0，而且 bin 0 之外的每个 bin 的幂也不总是 0.0f。我还尝试使用 for 循环在同一个线程上写入多个 bin，并且发生了同样的事情。我究竟做错了什么？

我有一种预感，这是问题根源所在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，这是错误的 CPU 端结果。

4

1 回答 1

0

问题解决了！

我用 aRWStructuredBuffer来表示 a RWByteOrderBuffer。不完全确定这是如何导致这一结果的，但确实如此。所以，FFT 结果现在是RWByteOrderBuffer. 不过，这个缓冲区的奇怪之处在于，D3DCSX 实现将浮点值间隔得如此之远——可能是出于缓存的原因，但老实说，我不太清楚为什么。这是我现在的计算着色器（这次计算分贝而不是功率 - 一个不相关的变化）：

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;
}

不过，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();

这就是为什么g_decibels仍然是一个RWStructuredBuffer.

我仍然不知道当只需要访问时结果缓冲区是否读/写是否重要 - 如果我更改g_result为常规ByteOrderBuffer我没有输出。但至少它现在正在工作。

于 2015-02-28T22:31:58.400 回答