C++-windows7下无法正常使用GetDIBits获取整个屏幕的截图，但XP是可以的，求指点

Question

    LPBITMAPINFO ptBmi;
    HWND         DeskHwnd;
    HDC          DeskHDC,ComHDC;
    HBITMAP      hBmp = 0;
    int          sdwRet;

    BITMAPINFO infoHeader;
    memset(&infoHeader.bmiHeader, 0, sizeof(BITMAPINFOHEADER));
    infoHeader.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    infoHeader.bmiHeader.biWidth       = x;
    infoHeader.bmiHeader.biHeight      = -y;
    infoHeader.bmiHeader.biPlanes      = 1;
    infoHeader.bmiHeader.biBitCount    = 32;
    infoHeader.bmiHeader.biCompression = BI_RGB;    

    /* 如果图像没有分配 */
    if (pImg->imageData == NULL)
    {
        char *data = new char[x * y * pImg->nChannels];
        cvSetData(pImg, data, pImg->widthStep);
    }

    //获取桌面窗口句柄
    //DeskHwnd = GetDesktopWindow();
    //获取桌面窗口DC
    //DeskHDC = GetWindowDC(DeskHwnd);
    //ComHDC = CreateCompatibleDC(DeskHDC);
    DeskHDC = ::GetDC(0);
    hBmp = (HBITMAP)GetCurrentObject(DeskHDC, 7);
    
    sdwRet = GetDIBits(DeskHDC, hBmp, 0, y, 
                       pImg->imageData, &infoHeader, 
                       DIB_RGB_COLORS);

Answer 1

首先，你的代码中有几个小问题：
你的cvSetData函数用途不明，对于截屏这个目的来说应该没有用处。
计算所需内存的表达式x * y * pImg->nChannels，明显是错误的。Bmp格式要求每行扫描线的数据对齐到4个字节，应该不是你这里的计算方式。
infoHeader.bmiHeader.biBitCount = 32;比较浪费空间，建议改成24（实际效果是一样的）。
GetCurrentObject(DeskHDC, 7);为什么不用OBJ_BITMAP？
最后，你的调用方式并不符合MSDN中的规范，XP下刚好能工作，并不等于这就是正确的。给你一个我自己用的截屏函数作为例子吧：

struct BmpHead : public BITMAPINFOHEADER
{
BmpHead(int x, int y, WORD bits = 24);
BITMAPINFO * operator & () {return (BITMAPINFO*)this;}
};

BmpHead::BmpHead(int x, int y, WORD bits)
{
biSize = sizeof(BITMAPINFOHEADER);
biWidth = x;
biHeight = y;
biPlanes = 1;
biBitCount = bits;
biCompression = BI_RGB;
int LineBytes = ((x * biBitCount + 31) & -32) >> 3;
biSizeImage = LineBytes * y;

biXPelsPerMeter = biYPelsPerMeter = 0;
biClrUsed = biClrImportant = 0;
}

void *WINAPI TakeScreenShot(const RECT &rect, HWND hWnd = NULL)
{
HDC hdcWnd = NULL;
HDC hdcCap = NULL;
HBITMAP bmpCap = NULL;
void *pData = NULL;
do
{
int x = rect.right - rect.left;
int y = rect.bottom - rect.top;
BmpHead bmi(x, y);

hdcWnd = ::GetDC(hWnd);
if (hdcWnd == NULL) break;
hdcCap = ::CreateCompatibleDC(hdcWnd);
if (hdcCap == NULL) break;
bmpCap = ::CreateCompatibleBitmap(hdcWnd, x, y);
if (bmpCap == NULL) break;

HGDIOBJ bmOld = ::SelectObject(hdcCap, bmpCap);
if (bmOld == NULL) break;
BOOL bSuccess = ::BitBlt(hdcCap, 0, 0, x, y,
hdcWnd, rect.left, rect.top, SRCCOPY);
::SelectObject(hdcCap, bmOld);
if (!bSuccess) break;

pData = malloc(bmi.biSizeImage);
if (pData == NULL) break;

DWORD dwRet = ::GetDIBits(hdcWnd, bmpCap, 0, y,
pData, &bmi, DIB_RGB_COLORS);
if (dwRet == 0)
{
free(pData);
pData = NULL;
}
}while(false);

if (hdcCap != NULL) ::DeleteDC(hdcCap);
if (bmpCap != NULL) ::DeleteObject(bmpCap);
if (hdcWnd != NULL) ::ReleaseDC(hWnd, hdcWnd);
return pData;
}