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c++directxdirect3ddirect3d11

D3D11 SwapChain Buffer is NULL

Whenever I run this code, the data that is pointed (member pData) to within the _TextureData struct is all 0 (like 300 bytes of just 0). The HRESULT result that it returns is always S_OK, and the row and column depths are accurate. I am sure that something is being rendered to the buffer because there are things being displayed on the window that I am rendering to. I have tried both getting the buffer's data before and after presenting, and either way, the data is still null.

D3D11_TEXTURE2D_DESC desc { };
ID3D11Texture2D * pCopy = nullptr;
ID3D11Texture2D * pBackBufferTexture = nullptr;
desc.Width = 800;
desc.Height = 800;
desc.MipLevels = 1;
desc.ArraySize = 1;
desc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
desc.SampleDesc.Count = 1;
desc.Usage = D3D11_USAGE_STAGING;
desc.BindFlags = 0;
desc.CPUAccessFlags = D3D11_CPU_ACCESS_READ;
desc.MiscFlags = 0;

assert( SUCCEEDED( pSwapChain->Present( 0,
                                        0 ) ) );
pDevice->CreateTexture2D( &desc, nullptr, &pCopy );
pSwapChain->GetBuffer( 0,
                       __uuidof( ID3D11Texture2D ),
                       reinterpret_cast< void ** >( &pBackBufferTexture ) );
pContext->CopyResource( pCopy, pBackBufferTexture );
D3D11_MAPPED_SUBRESOURCE _TextureData { };
auto result = pContext->Map( pCopy, 0, D3D11_MAP_READ, 0, &_TextureData );
pContext->Unmap( pCopy, 0 );
pCopy->Release( );
Solution

  • The code for the swapchain holds the answer... The swap-chain was created with 4x MSAA, but the staging texture is single-sample.

    You can't CopyResource in this case. Instead you must resolve the MSAA:

    pContext->ResolveSubresource(pCopy, 0, pBackBufferTexture, 0, DXGI_FORMAT_R8G8B8A8_UNORM);

    See the DirectX Tool Kit ScreenGrab source which handles this case more generally.

    The code also shows that you are not using the Debug device (D3D11_CREATE_DEVICE_DEBUG) which would have told you about this problem. See this blog post for details.