FFMPEG录屏（14）---- WGC 捕获桌面(二) Copy数据到CPU

本文链接：https://blog.youkuaiyun.com/peilinok/article/details/129573199

该文章介绍了如何使用WebRTC进行屏幕捕获后，将捕获的窗口或桌面内容从GPU复制到内存中，以便进行后续处理如压缩。通过D3D11接口创建映射纹理，然后在帧到达时进行资源复制，并将数据保存为位图文件。

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参考资料

WEBRTC WGC CAPTURE

上一篇中我们已经成功改造官网Demo用以捕获显示器内容，现在我们支持了捕获窗口、桌面并实时的渲染在窗口中，下一步我们需要把捕获到的数据从GPU拷贝出来到我们的内存中用以压缩等等。

话不多说直接上代码

SimpleCapture.h 中添加成员变量 m_mappedTexture

winrt::com_ptr<ID3D11Texture2D> m_mappedTexture{nullptr};

SimpleCapture.h 中添加成员函数 CreateMappedTexture

HRESULT
CreateMappedTexture(winrt::com_ptr<ID3D11Texture2D> src_texture,
                    UINT width = 0, UINT height = 0);

SimpleCapture.cpp 中添加实现 CreateMappedTexture

HRESULT
SimpleCapture::CreateMappedTexture(winrt::com_ptr<ID3D11Texture2D> src_texture,
                                   UINT width, UINT height) {
  D3D11_TEXTURE2D_DESC src_desc;
  src_texture->GetDesc(&src_desc);
  D3D11_TEXTURE2D_DESC map_desc;
  map_desc.Width = width == 0 ? src_desc.Width : width;
  map_desc.Height = height == 0 ? src_desc.Height : height;
  map_desc.MipLevels = src_desc.MipLevels;
  map_desc.ArraySize = src_desc.ArraySize;
  map_desc.Format = src_desc.Format;
  map_desc.SampleDesc = src_desc.SampleDesc;
  map_desc.Usage = D3D11_USAGE_STAGING;
  map_desc.BindFlags = 0;
  map_desc.CPUAccessFlags = D3D11_CPU_ACCESS_READ;
  map_desc.MiscFlags = 0;

  auto d3dDevice = GetDXGIInterfaceFromObject<ID3D11Device>(m_device);

  return d3dDevice->CreateTexture2D(&map_desc, nullptr, m_mappedTexture.put());
}

SimpleCapture.cpp 中 OnFrameArrived 函数中添加代码

// copy to mapped texture
{
  auto frameSurface =
      GetDXGIInterfaceFromObject<ID3D11Texture2D>(frame.Surface());

  if (!m_mappedTexture || newSize)
    CreateMappedTexture(frameSurface);

  m_d3dContext->CopyResource(m_mappedTexture.get(), frameSurface.get());

  D3D11_MAPPED_SUBRESOURCE mapInfo;
  m_d3dContext->Map(m_mappedTexture.get(), 0, D3D11_MAP_READ,
                    D3D11_MAP_FLAG_DO_NOT_WAIT, &mapInfo);
                    
  // copy data from mapInfo.pData
  
  m_d3dContext->Unmap(m_mappedTexture.get(), 0);
}

保存为位图文件看看？

#if 1
if (mapInfo.pData) {
  static unsigned char *buffer = nullptr;
  if (buffer && newSize)
    delete[] buffer;

  if (!buffer)
    buffer = new unsigned char[frameContentSize.Width *
                                frameContentSize.Height * 4];

  int dstRowPitch = frameContentSize.Width * 4;
  for (int h = 0; h < frameContentSize.Height; h++) {
    memcpy_s(buffer + h * dstRowPitch, dstRowPitch,
              (BYTE *)mapInfo.pData + h * mapInfo.RowPitch,
              min(mapInfo.RowPitch, dstRowPitch));
  }

  BITMAPINFOHEADER bi;

  bi.biSize = sizeof(BITMAPINFOHEADER);
  bi.biWidth = frameContentSize.Width;
  bi.biHeight = frameContentSize.Height * (-1);
  bi.biPlanes = 1;
  bi.biBitCount = 32; // should get from system color bits
  bi.biCompression = BI_RGB;
  bi.biSizeImage = 0;
  bi.biXPelsPerMeter = 0;
  bi.biYPelsPerMeter = 0;
  bi.biClrUsed = 0;
  bi.biClrImportant = 0;

  BITMAPFILEHEADER bf;
  bf.bfType = 0x4d42;
  bf.bfReserved1 = 0;
  bf.bfReserved2 = 0;
  bf.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
  bf.bfSize =
      bf.bfOffBits + frameContentSize.Width * frameContentSize.Height * 4;

  FILE *fp = nullptr;

  fopen_s(&fp, ".\\save.bmp", "wb+");

  fwrite(&bf, 1, sizeof(bf), fp);
  fwrite(&bi, 1, sizeof(bi), fp);
  fwrite(buffer, 1, frameContentSize.Width * frameContentSize.Height * 4,
          fp);

  fflush(fp);
  fclose(fp);
}
#endif