DirectN

Direct Wrappers for .NET : DXGI, WIC, DirectX 9 to 12, Direct2D, Direct Write, Media Foundation, WASAPI, CodecAPI, GDI, Spatial Audio, DVD, Windows Media Player, etc.

The easiest way to use this is reference the nuget package: https://www.nuget.org/packages/DirectN/

Or you can pick the C# source files you want (among the 6000 .cs provided), but it can be difficult because the dependencies between all these technologies make extracting a small portion quite difficult (and they are one of the reasons why DirectN exists...).

DirectN allows you to port C/C++ code to C#, or to write C# code from scratch, more easily than with other existing interop libraries in this domain because one of its main objective is to use exactly the same names and types (interfaces, enums, structures, constants, methods, arguments, guids, etc.) that the native concepts. So you can read the official documentation, use existing C/C++ samples, and start coding with .NET right away.

Everything is in the same namespace so you don't need to know where is defined this or that interface, constants, etc.

For example, the exact same C# version of the "Capture screen using DirectX" code here: https://stackoverflow.com/questions/30021274/capture-screen-using-directx is this:

static HRESULT Direct3D9TakeScreenshots(uint adapter, int count)
{
    using (var d3d = new ComObject<IDirect3D9>(Functions.Direct3DCreate9(Constants.D3D_SDK_VERSION)))
    {
        var mode = new _D3DDISPLAYMODE();
        d3d.Object.GetAdapterDisplayMode(adapter, ref mode).ThrowOnError();

        var parameters = new _D3DPRESENT_PARAMETERS_();
        parameters.Windowed = true;
        parameters.BackBufferCount = 1;
        parameters.BackBufferHeight = mode.Height;
        parameters.BackBufferWidth = mode.Width;
        parameters.SwapEffect = _D3DSWAPEFFECT.D3DSWAPEFFECT_DISCARD;

        d3d.Object.CreateDevice(adapter, _D3DDEVTYPE.D3DDEVTYPE_HAL, IntPtr.Zero, Constants.D3DCREATE_SOFTWARE_VERTEXPROCESSING, ref parameters, out var dev).ThrowOnError();
        using (var device = new ComObject<IDirect3DDevice9>(dev))
        {
            dev.CreateOffscreenPlainSurface(mode.Width, mode.Height, _D3DFORMAT.D3DFMT_A8R8G8B8, _D3DPOOL.D3DPOOL_SYSTEMMEM, out var surf, IntPtr.Zero).ThrowOnError();
            using (var surface = new ComObject<IDirect3DSurface9>(surf))
            {
                var rc = new _D3DLOCKED_RECT();
                var rect = new tagRECT();
                surf.LockRect(ref rc, ref rect, 0).ThrowOnError();
                var pitch = rc.Pitch;
                surf.UnlockRect();

                var shots = new byte[count][];
                for (var i = 0; i < count; i++)
                {
                    shots[i] = new byte[pitch * mode.Height];
                }

                var sw = new Stopwatch();
                sw.Start();
                for (var i = 0; i < count; i++)
                {
                    dev.GetFrontBufferData(0, surf).ThrowOnError();
                    surf.LockRect(ref rc, ref rect, 0).ThrowOnError();
                    Marshal.Copy(rc.pBits, shots[i], 0, shots[i].Length);
                    surf.UnlockRect().ThrowOnError();
                }
                Console.WriteLine("Elapsed: " + sw.Elapsed);

                for (var i = 0; i < count; i++)
                {
                    SavePixelsToFile32bppPBGRA(mode.Width, mode.Height, (uint)pitch, shots[i], "cap" + i + ".png", WICConstants.GUID_ContainerFormatPng).ThrowOnError();
                }
            }
        }
    }
    return 0;
}

static HRESULT SavePixelsToFile32bppPBGRA(uint width, uint height, uint stride, byte[] pixels, string filePath, Guid format)
{
    if (filePath == null)
        throw new ArgumentNullException(nameof(filePath));

    using (var fac = new ComObject<IWICImagingFactory>((IWICImagingFactory)new WicImagingFactory()))
    {
        fac.Object.CreateStream(out var stream).ThrowOnError();
        using (new ComObject<IWICStream>(stream))
        {
            const int GENERIC_WRITE = 0x40000000;
            stream.InitializeFromFilename(filePath, GENERIC_WRITE).ThrowOnError();
            fac.Object.CreateEncoder(format, IntPtr.Zero, out var encoder).ThrowOnError();
            using (new ComObject<IWICBitmapEncoder>(encoder))
            {
                encoder.Initialize(stream, WICBitmapEncoderCacheOption.WICBitmapEncoderNoCache).ThrowOnError();
                encoder.CreateNewFrame(out var frame, out var bag).ThrowOnError();
                using (new ComObject<IWICBitmapFrameEncode>(frame))
                {
                    frame.Initialize(null).ThrowOnError();
                    frame.SetSize(width, height).ThrowOnError();
                    frame.SetPixelFormat(ref format).ThrowOnError();
                    frame.WritePixels(height, stride, stride * height, pixels).ThrowOnError();
                    frame.Commit().ThrowOnError();
                    encoder.Commit().ThrowOnError();
                }
            }
        }
    }
    return 0;
}

And the C++ version is this:

  HRESULT Direct3D9TakeScreenshots(UINT adapter, UINT count)
  {
    HRESULT hr = S_OK;
    IDirect3D9 *d3d = nullptr;
    IDirect3DDevice9 *device = nullptr;
    IDirect3DSurface9 *surface = nullptr;
    D3DPRESENT_PARAMETERS parameters = { 0 };
    D3DDISPLAYMODE mode;
    D3DLOCKED_RECT rc;
    UINT pitch;
    SYSTEMTIME st;
    LPBYTE *shots = nullptr;

    // init D3D and get screen size
    d3d = Direct3DCreate9(D3D_SDK_VERSION);
    HRCHECK(d3d->GetAdapterDisplayMode(adapter, &mode));

    parameters.Windowed = TRUE;
    parameters.BackBufferCount = 1;
    parameters.BackBufferHeight = mode.Height;
    parameters.BackBufferWidth = mode.Width;
    parameters.SwapEffect = D3DSWAPEFFECT_DISCARD;
    parameters.hDeviceWindow = NULL;

    // create device & capture surface
    HRCHECK(d3d->CreateDevice(adapter, D3DDEVTYPE_HAL, NULL, D3DCREATE_SOFTWARE_VERTEXPROCESSING, &parameters, &device));
    HRCHECK(device->CreateOffscreenPlainSurface(mode.Width, mode.Height, D3DFMT_A8R8G8B8, D3DPOOL_SYSTEMMEM, &surface, nullptr));

    // compute the required buffer size
    HRCHECK(surface->LockRect(&rc, NULL, 0));
    pitch = rc.Pitch;
    HRCHECK(surface->UnlockRect());

    // allocate screenshots buffers
    shots = new LPBYTE[count];
    for (UINT i = 0; i < count; i++)
    {
      shots[i] = new BYTE[pitch * mode.Height];
    }

    GetSystemTime(&st); // measure the time we spend doing <count> captures
    wprintf(L"%i:%i:%i.%i\n", st.wHour, st.wMinute, st.wSecond, st.wMilliseconds);
    for (UINT i = 0; i < count; i++)
    {
      // get the data
      HRCHECK(device->GetFrontBufferData(0, surface));

      // copy it into our buffers
      HRCHECK(surface->LockRect(&rc, NULL, 0));
      CopyMemory(shots[i], rc.pBits, rc.Pitch * mode.Height);
      HRCHECK(surface->UnlockRect());
    }
    GetSystemTime(&st);
    wprintf(L"%i:%i:%i.%i\n", st.wHour, st.wMinute, st.wSecond, st.wMilliseconds);

    // save all screenshots
    for (UINT i = 0; i < count; i++)
    {
      WCHAR file[100];
      wsprintf(file, L"cap%i.png", i);
      HRCHECK(SavePixelsToFile32bppPBGRA(mode.Width, mode.Height, pitch, shots[i], file, GUID_ContainerFormatPng));
    }

  cleanup:
    if (shots != nullptr)
    {
      for (UINT i = 0; i < count; i++)
      {
        delete shots[i];
      }
      delete[] shots;
    }
    RELEASE(surface);
    RELEASE(device);
    RELEASE(d3d);
    return hr;
  }

   HRESULT SavePixelsToFile32bppPBGRA(UINT width, UINT height, UINT stride, LPBYTE pixels, LPWSTR filePath, const GUID &format)
  {
    if (!filePath || !pixels)
      return E_INVALIDARG;

    HRESULT hr = S_OK;
    IWICImagingFactory *factory = nullptr;
    IWICBitmapEncoder *encoder = nullptr;
    IWICBitmapFrameEncode *frame = nullptr;
    IWICStream *stream = nullptr;
    GUID pf = GUID_WICPixelFormat32bppPBGRA;
    BOOL coInit = CoInitialize(nullptr);

    HRCHECK(CoCreateInstance(CLSID_WICImagingFactory, nullptr, CLSCTX_INPROC_SERVER, IID_PPV_ARGS(&factory)));
    HRCHECK(factory->CreateStream(&stream));
    HRCHECK(stream->InitializeFromFilename(filePath, GENERIC_WRITE));
    HRCHECK(factory->CreateEncoder(format, nullptr, &encoder));
    HRCHECK(encoder->Initialize(stream, WICBitmapEncoderNoCache));
    HRCHECK(encoder->CreateNewFrame(&frame, nullptr)); // we don't use options here
    HRCHECK(frame->Initialize(nullptr)); // we dont' use any options here
    HRCHECK(frame->SetSize(width, height));
    HRCHECK(frame->SetPixelFormat(&pf));
    HRCHECK(frame->WritePixels(height, stride, stride * height, pixels));
    HRCHECK(frame->Commit());
    HRCHECK(encoder->Commit());

  cleanup:
    RELEASE(stream);
    RELEASE(frame);
    RELEASE(encoder);
    RELEASE(factory);
    if (coInit) CoUninitialize();
    return hr;
  }

• Note 1: there are currently some issues with sructures that contain unions. This will be fixed soon. If you have a specific problem with that, just create an issue
• Note 2: the functions.cs file has some issues. everything in the Generated folder is, well, automatically generated. If you have a specific problem with that, just create an issue
• Note 3: the tool that builds the Generated folder is not open source.