c - 截屏代码产生黑色位图

Question

我需要添加截取整个屏幕的功能，而不仅仅是当前窗口。下面的代码生成一个尺寸正确的 bmp 文件，但图像是全黑的。我做错了什么？

void CaptureScreen(LPCTSTR lpszFilePathName)
{
      BITMAPFILEHEADER   bmfHeader;
      BITMAPINFO                *pbminfo;
      HBITMAP                   hBmp;
      FILE                      *oFile;
      HDC      screen;
   HDC      memDC;
   int      sHeight;  
   int      sWidth;   
      LPBYTE     pBuff;
   BITMAP     bmp;
   WORD      cClrBits; 
   RECT      rcClient;


   screen = GetDC(0);
   memDC = CreateCompatibleDC(screen);

   sHeight = GetDeviceCaps(screen, VERTRES);
   sWidth = GetDeviceCaps(screen, HORZRES);

   //GetObject(screen, sizeof(BITMAP), &bmp);

   hBmp    = CreateCompatibleBitmap ( screen, sWidth, sHeight );

   // Retrieve the bitmap color format, width, and height.  
 GetObject(hBmp, sizeof(BITMAP), (LPSTR)&bmp) ;

    // Convert the color format to a count of bits.  
    cClrBits = (WORD)(bmp.bmPlanes * bmp.bmBitsPixel); 
    if (cClrBits == 1) 
        cClrBits = 1; 
    else if (cClrBits bmiHeader.biSize = sizeof(BITMAPINFOHEADER); 
    pbminfo->bmiHeader.biWidth = bmp.bmWidth; 
    pbminfo->bmiHeader.biHeight = bmp.bmHeight; 
    pbminfo->bmiHeader.biPlanes = bmp.bmPlanes; 
    pbminfo->bmiHeader.biBitCount = bmp.bmBitsPixel; 
    if (cClrBits bmiHeader.biClrUsed = (1bmiHeader.biCompression = BI_RGB; 

    // Compute the number of bytes in the array of color  
    // indices and store the result in biSizeImage.  
    // The width must be DWORD aligned unless the bitmap is RLE 
    // compressed. 
    pbminfo->bmiHeader.biSizeImage = ((pbminfo->bmiHeader.biWidth * cClrBits +31) & ~31) /8
                                  * pbminfo->bmiHeader.biHeight; 
    // Set biClrImportant to 0, indicating that all of the  
    // device colors are important.  
     pbminfo->bmiHeader.biClrImportant = 0; 

  CreateBMPFile(lpszFilePathName, pbminfo, hBmp, memDC);
}

void CreateBMPFile(LPTSTR pszFile, PBITMAPINFO pbi, 
                  HBITMAP hBMP, HDC hDC) 
 { 
     HANDLE hf;                 // file handle  
    BITMAPFILEHEADER hdr;       // bitmap file-header  
    PBITMAPINFOHEADER pbih;     // bitmap info-header  
    LPBYTE lpBits;              // memory pointer  
    DWORD dwTotal;              // total count of bytes  
    DWORD cb;                   // incremental count of bytes  
    BYTE *hp;                   // byte pointer  
    DWORD dwTmp; 
 int lines;

    pbih = (PBITMAPINFOHEADER) pbi; 
    lpBits = (LPBYTE) GlobalAlloc(GMEM_FIXED, pbih->biSizeImage);

    // Retrieve the color table (RGBQUAD array) and the bits  
    // (array of palette indices) from the DIB.  
    lines = GetDIBits(hDC, hBMP, 0, (WORD) pbih->biHeight, lpBits, pbi, 
        DIB_RGB_COLORS);

    // Create the .BMP file.  
    hf = CreateFile(pszFile, 
                   GENERIC_READ | GENERIC_WRITE, 
                   (DWORD) 0, 
                    NULL, 
                   CREATE_ALWAYS, 
                   FILE_ATTRIBUTE_NORMAL, 
                   (HANDLE) NULL); 

    hdr.bfType = 0x4d42;        // 0x42 = "B" 0x4d = "M"  
    // Compute the size of the entire file.  
    hdr.bfSize = (DWORD) (sizeof(BITMAPFILEHEADER) + 
                 pbih->biSize + pbih->biClrUsed 
                 * sizeof(RGBQUAD) + pbih->biSizeImage); 
    hdr.bfReserved1 = 0; 
    hdr.bfReserved2 = 0; 

    // Compute the offset to the array of color indices.  
    hdr.bfOffBits = (DWORD) sizeof(BITMAPFILEHEADER) + 
                    pbih->biSize + pbih->biClrUsed 
                    * sizeof (RGBQUAD); 

    // Copy the BITMAPFILEHEADER into the .BMP file.  
    WriteFile(hf, (LPVOID) &hdr, sizeof(BITMAPFILEHEADER), 
        (LPDWORD) &dwTmp,  NULL);

    // Copy the BITMAPINFOHEADER and RGBQUAD array into the file.  
    WriteFile(hf, (LPVOID) pbih, sizeof(BITMAPINFOHEADER) 
                  + pbih->biClrUsed * sizeof (RGBQUAD), 
                  (LPDWORD) &dwTmp, ( NULL));

    // Copy the array of color indices into the .BMP file.  
    dwTotal = cb = pbih->biSizeImage; 
    hp = lpBits; 
    WriteFile(hf, (LPSTR) hp, (int) cb, (LPDWORD) &dwTmp,NULL);
    // Close the .BMP file.  
 CloseHandle(hf);
    // Free memory.  
    GlobalFree((HGLOBAL)lpBits);
}

Answer 1

CaptureScreen 函数所做的只是创建一个与屏幕大小相同的兼容位图，然后将其写入磁盘，因此您看到的是位图的默认内容(黑色)。要捕获屏幕，您需要创建一个兼容的 DC，选择您制作的位图并从一个 DC 到另一个 DC。然后，您需要在开始写入文件之前取消选择目标位图。