使用 Winsock、GetDIBits 和 SetDiBits 进行位图传输

Question

我开始使用 C++ 开发类似于远程控制应用程序的东西。我希望将特定窗口的屏幕截图传输到另一台电脑并将其显示在窗口中。 GetDIBits 和 SetDIBits 函数都成功，连接建立，数据发送，但另一端没有出现图像，只是一片漆黑。

这是我的发送代码：

void GetScreenData(BITMAPINFO* bi, BYTE* buf) //gets the bitmap data
{
  HBITMAP hBitmap;
  BITMAP Bitmap;
  RECT r;

  HDC ActiveDC = GetDC(hActive);
  HDC CopyDC = CreateCompatibleDC(ActiveDC);

  GetWindowRect(hActive, &r);

  int scrWidth = r.right-r.left;
  int scrHeight = r.bottom-r.top;

  hBitmap = CreateCompatibleBitmap(ActiveDC, scrWidth, scrHeight);
  SelectObject(CopyDC, hBitmap);

  BitBlt(CopyDC, 0, 0, scrWidth, scrHeight, ActiveDC, 0, 0, SRCCOPY);

  GetObject(hBitmap, sizeof(BITMAP), &Bitmap);

  int cClrBits = Bitmap.bmPlanes*Bitmap.bmBitsPixel;

  memset(bi, 0, sizeof(BITMAPINFO));

  bi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
  bi->bmiHeader.biWidth = Bitmap.bmWidth;
  bi->bmiHeader.biHeight = Bitmap.bmHeight;
  bi->bmiHeader.biPlanes = Bitmap.bmPlanes;
  bi->bmiHeader.biBitCount = Bitmap.bmBitsPixel;

  if(cClrBits<24)
  {
    bi->bmiHeader.biClrUsed = (1<<cClrBits);
  }

  bi->bmiHeader.biCompression = BI_RGB;
  bi->bmiHeader.biSizeImage = ((bi->bmiHeader.biWidth * cClrBits +31) & ~31)/8*bi->bmiHeader.biHeight;

  int i = GetDIBits(CopyDC, hBitmap, 0, scrHeight, buf, bi, DIB_RGB_COLORS);

  printf("GetDIBits returned %i\n", i);

  ReleaseDC(hActive, ActiveDC);
  DeleteDC(CopyDC);
}

DWORD WINAPI SendImage(LPVOID param) //sends the bitmap data
{
  BITMAPINFO bi;
  BYTE* data = new BYTE[256*256*256];
  BYTE* buf = new BYTE[256*256*256];
  BYTE *packetsize1, *packetsize2;
  int biSize = sizeof(BITMAPINFO);
  int i, clocks, oldclocks=0;

  while(true)
  {
    clocks=clock();

    if((clocks-oldclocks)*CLOCKS_PER_SEC<0.1)
    {
      continue;
    }

    oldclocks=clocks;

    if(bConnected)
    {
      GetScreenData(&bi, buf);

      i=0;

      data[i++]=3;
      packetsize1=&data[i++];
      packetsize2=&data[i++];

      memcpy(data+i, &bi, biSize);

      i+=biSize;

      memcpy(data+i, buf, bi.bmiHeader.biSizeImage);

      printf("Sending image...\n");

      i+=bi.bmiHeader.biSizeImage;

      *packetsize1=int(i/256);
      *packetsize2=int(i%256);

      send(s, (char*)data, i, 0);
    }
  }
}

这是接收方：

void DrawScreen(HDC hdc) //called from windows message WM_PAINT
{
  HGDIOBJ hobj;

  hobj = SelectObject(RemoteDC, hRemoteBitmap);

  BitBlt(hdc, 0, 0, scrWidth, scrHeight, RemoteDC, 0, 0, SRCCOPY);

  SelectObject(hdc, hobj);
}

DWORD WINAPI RecvData(LPVOID param)
{
  BYTE* data = new BYTE[256*256*256];
  int packetsize, num;
  int newWidth, newHeight;
  int recvimgsize=0;

  bool bAwaitingImage = false;

  while(true)
  {
    if(bConnected)
    {
      num=recv(s, (char*)data, 3, 0);

      if(num>0)
      {
        packetsize = data[1]*256+data[2];

        num=recv(s, (char*)(data+3), packetsize-3, 0);
      }

      if(num>0)
      {
        switch(data[0])
        {
          case 2: //received information about window size (image size)
            newWidth = data[3]*256+data[4];
            newHeight = data[5]*256+data[6];

            if(newHeight!=scrHeight || newWidth!=scrWidth)
            {
              scrWidth = newWidth;
              scrHeight = newHeight;

              RECT r;

              GetWindowRect(hwnd, &r);
              SetWindowPos(hwnd, NULL, r.left, r.top, scrWidth, scrHeight, 0);

              HDC ThisDC = GetDC(hwnd);

              DeleteDC(RemoteDC);
              RemoteDC = CreateCompatibleDC(ThisDC);

              DeleteObject(hRemoteBitmap);
              hRemoteBitmap = CreateCompatibleBitmap(ThisDC, scrWidth, scrHeight);

              SelectObject(RemoteDC, hRemoteBitmap);

              ReleaseDC(hwnd, ThisDC);
            }
            break;
          case 3:
          {
            BITMAPINFO bi;
            HBITMAP hBitmap;

            int biSize = sizeof(BITMAPINFO);
            memcpy(&bi, data+3, biSize);
            SetDIBits(RemoteDC, hRemoteBitmap, 0, scrHeight, data+biSize+3, &bi, DIB_RGB_COLORS);

            InvalidateRect(hwnd, NULL, false);

            break;
          }
        }

        continue;
      }

      if(num==0)
      {
        //connection closed
        bConnected=false;
      }else{
        //error
        bConnected=false;
      }
    }
  }
}

我在这里提供的代码有点长，因为我不确定什么可能有用。先感谢您。

Answer 1

发布代码的问题在于，为总传输数据长度分配了两个 BYTE（[data+1] 和 [data+2]）。两个字节可处理最多 64K 的数据，而图像很容易超出这个范围，不会检查 i 值是否溢出。

为了使代码片段恢复活力，需要在其中添加位，以便它们可以保持真实的长度。也就是说，应该有一个或两个附加字节来使数据包长度为 24 或 32 位值。

Answer 2

我分配的字节数不足以存储数据包大小，现在我增加了该数字，它就可以工作了。 ;-)