屏幕截图代码产生黑色位图

Question

我需要添加截屏整个屏幕的功能，而不仅仅是当前窗口。以下代码会生成正确尺寸的bmp文件，但图像完全是黑色的。我究竟做错了什么？

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

所有CaptureScreen功能确实是创建一个兼容的位图的尺寸与屏幕相同，然后将其写入到磁盘上，所以你看到的位图（黑色）的默认内容。要捕捉屏幕，您需要创建一个兼容的DC，选择您制作的位图并从一个DC传输到另一个DC。然后，在开始写入文件之前，您需要取消选择您的目标位图。