Desktop Duplication API returns empty frame - directx

Question

I am aware that there are already a few questions asking this or similar things and I dived into a few of them, but without any success.
I try to capture a "screenshot" of my display using the Desktop duplication API and process pixeldata of it. Later I would like to do that at least 30 times/second, but thats a different case.
For now, I tried the example of microsoft: https://github.com/microsoftarchive/msdn-code-gallery-microsoft/tree/master/Official%20Windows%20Platform%20Sample/DXGI%20desktop%20duplication%20sample
I successfully saved a picture of the screen and accessed the pixel data with that code.
DirectX::ScratchImage image;
hr = DirectX::CaptureTexture(m_Device, m_DeviceContext, m_AcquiredDesktopImage, image);
hr = DirectX::SaveToDDSFile(image.GetImages(), image.GetImageCount(), image.GetMetadata(), DirectX::DDS_FLAGS_NONE, L"test.dds");
uint8_t* pixels;
pixels = image.GetPixels();
Now I wanted to break the example code down to the basic stuff I need. As I am not familiar with DirectX I have a hard time doing that.
I came up with following code, which runs without error but produces an empty picture. I check hr in Debug Mode, I am aware that this is bad practice and dirty!
int main()
{
HRESULT hr = S_OK;
ID3D11Device* m_Device;
ID3D11DeviceContext* m_DeviceContext;
// Driver types supported
D3D_DRIVER_TYPE DriverTypes[] =
{
D3D_DRIVER_TYPE_HARDWARE,
D3D_DRIVER_TYPE_WARP,
D3D_DRIVER_TYPE_REFERENCE,
};
UINT NumDriverTypes = ARRAYSIZE(DriverTypes);
// Feature levels supported
D3D_FEATURE_LEVEL FeatureLevels[] =
{
D3D_FEATURE_LEVEL_11_0,
D3D_FEATURE_LEVEL_10_1,
D3D_FEATURE_LEVEL_10_0,
D3D_FEATURE_LEVEL_9_1
};
UINT NumFeatureLevels = ARRAYSIZE(FeatureLevels);
D3D_FEATURE_LEVEL FeatureLevel;
// Create device
for (UINT DriverTypeIndex = 0; DriverTypeIndex < NumDriverTypes; ++DriverTypeIndex)
{
hr = D3D11CreateDevice(nullptr, DriverTypes[DriverTypeIndex], nullptr, 0, FeatureLevels, NumFeatureLevels,
D3D11_SDK_VERSION, &m_Device, &FeatureLevel, &m_DeviceContext);
if (SUCCEEDED(hr))
{
// Device creation success, no need to loop anymore
break;
}
}
IDXGIOutputDuplication* m_DeskDupl;
IDXGIOutput1* DxgiOutput1 = nullptr;
IDXGIOutput* DxgiOutput = nullptr;
IDXGIAdapter* DxgiAdapter = nullptr;
IDXGIDevice* DxgiDevice = nullptr;
UINT Output = 0;
hr = m_Device->QueryInterface(__uuidof(IDXGIDevice), reinterpret_cast<void**>(&DxgiDevice));
hr = DxgiDevice->GetParent(__uuidof(IDXGIAdapter), reinterpret_cast<void**>(&DxgiAdapter));
DxgiDevice->Release();
DxgiDevice = nullptr;
hr = DxgiAdapter->EnumOutputs(Output, &DxgiOutput);
DxgiAdapter->Release();
DxgiAdapter = nullptr;
hr = DxgiOutput->QueryInterface(__uuidof(DxgiOutput1), reinterpret_cast<void**>(&DxgiOutput1));
DxgiOutput->Release();
DxgiOutput = nullptr;
hr = DxgiOutput1->DuplicateOutput(m_Device, &m_DeskDupl);
IDXGIResource* DesktopResource = nullptr;
DXGI_OUTDUPL_FRAME_INFO FrameInfo;
hr = m_DeskDupl->AcquireNextFrame(500, &FrameInfo, &DesktopResource);
ID3D11Texture2D* m_AcquiredDesktopImage;
hr = DesktopResource->QueryInterface(__uuidof(ID3D11Texture2D), reinterpret_cast<void**>(&m_AcquiredDesktopImage));
DesktopResource->Release();
DesktopResource = nullptr;
DirectX::ScratchImage image;
hr = DirectX::CaptureTexture(m_Device, m_DeviceContext, m_AcquiredDesktopImage, image);
hr = DirectX::SaveToDDSFile(image.GetImages(), image.GetImageCount(), image.GetMetadata(), DirectX::DDS_FLAGS_NONE, L"test.dds");
uint8_t* pixels;
pixels = image.GetPixels();
hr = m_DeskDupl->ReleaseFrame();
}
Could anyone give me a hint what is wrong with this code?
EDIT:
Just found the code snipet below and integrated it into my code.
Now it works!
Lessons learnt:
-) actully output/process hr!
-) AcquireNextFrame might not work on first try (?)
I might update this post again with better code, with functioning loop.
int lTryCount = 4;
do
{
Sleep(100);
hr = m_DeskDupl->AcquireNextFrame(250, &FrameInfo, &DesktopResource);
if (SUCCEEDED(hr))
break;
if (hr == DXGI_ERROR_WAIT_TIMEOUT)
{
continue;
}
else if (FAILED(hr))
break;
} while (--lTryCount > 0);

Answer 1

AcquireNextFrame is allowed to return null resource (texture) because it returns on either change in desktop image or change related to pointer.
AcquireNextFrame acquires a new desktop frame when the operating system either updates the desktop bitmap image or changes the shape or position of a hardware pointer.
When you start frame acquisition you apparently are to get first desktop image soon, but you can also have a few of pointer notifications too before the image.
You should not limit yourself with 4 attempts and you don't need to sleep within the loop. Just keep polling for the image. To avoid dead loop it makes more sense to track total time spent in the loop and limit it to, for example, one second.
See also:
AcquireNextFrame() never grabs an updated image, always blank