Unable to implement DIB printing with GDI (MFC)

[TX_]

MFC doc/view architecture, GDI drawing/printing. I have a DIB backbuffer I need to display and print.

After the long and painful road I came to the conclusion than I need to use DIB created with CreateDIBSection (rather than DDB created with CreateCompatibleBitmap), and I have to blit it onto printer dc with StretchDIBits (rather than StretchBlt).

But i'm not able to get this thing to work.

Here is what I do:

In my initialization routine, I setup the backbuffer, like this:

    // Prepare device context:

    CClientDC aDC(this);
    OnPrepareDC(&aDC);

    // Setup proper backbuffer:

    _pMemDc = new CDC;
    _pMemDc->CreateCompatibleDC(&aDC);

    memset(&_bitmapInfo, 0, sizeof(BITMAPINFO));

    _bitmapInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    _bitmapInfo.bmiHeader.biWidth = _sizeBackBuffer.cx;
    _bitmapInfo.bmiHeader.biHeight = -_sizeBackBuffer.cy; // top-down
    _bitmapInfo.bmiHeader.biPlanes = 1;
    _bitmapInfo.bmiHeader.biBitCount = 24; // Maybe 32?
    _bitmapInfo.bmiHeader.biCompression = BI_RGB;

    HANDLE hMemBitmap = CreateDIBSection(aDC.GetSafeHdc(), &_bitmapInfo, DIB_RGB_COLORS, (void**)&_pBitmapRawBits, 0, 0);

    _hOldSelBitmap = (HBITMAP)_pMemDc->SelectObject(hMemBitmap); 

Variables with underscores are (private) member variables, declared like this:

    CDC *_pMemDc; // Backbuffer memory dc
    HBITMAP _hOldSelBitmap;

    BITMAPINFO _bitmapInfo; // Backbuffer DIB (header-only)
    unsigned char *_pBitmapRawBits; // Pointer to pixel data of DIB

    SIZE _sizeBackBuffer; // Size of backbuffer, i.e. size of that DIB 

Now below is what I do in my OnDraw override:

Firstly I get the area to be drawn like this (simplified code):

    CRect rectClipBoxPlayground;

    if (pDC->IsPrinting())
    {
        rectClipBoxPlayground = _printingParams.pPrintInfo->m_rectDraw;
    }
    else
    {
        pDC->GetClipBox(&rectClipBoxPlayground);
    } 

Then I calculate the corresponding rect coordinates in my backbuffer, which is usually (much) larger than the DC. Details of this calculation are irrelevant here, I just say that

CRect rectClipBoxBackBuffer;

represents the corresponding rect of backbuffer (in pixel coordinates of backbuffer).

Then I draw onto my backbuffer, using the _pMemDc memory dc.

And finally comes the part where I have troubles: blitting my DIB onto target dc (screen or printer). Here is what I do:

    // Copy back buffer to screen/printer dc:

    pDC->SetStretchBltMode(HALFTONE);
    SetBrushOrgEx(pDC->GetSafeHdc(), 0, 0, 0);

    // BELOW COMMENTED CODE OF StretchBlt WORKS(!) INSTEAD OF StretchDIBits.
    //
    //BOOL bSuccess = pDC->StretchBlt(rectClipBoxPlayground.left, rectClipBoxPlayground.top, 
    //    rectClipBoxPlayground.Width(), rectClipBoxPlayground.Height(), 
    //    _pMemDc, rectClipBoxBackBuffer.left, rectClipBoxBackBuffer.top, 
    //    rectClipBoxBackBuffer.Width(), rectClipBoxBackBuffer.Height(), SRCCOPY);

    HBITMAP hMemBitmap = (HBITMAP)_pMemDc->SelectObject(_hOldSelBitmap);

    DWORD dwLines = StretchDIBits(pDC->GetSafeHdc(), 
        rectClipBoxPlayground.left, rectClipBoxPlayground.top, rectClipBoxPlayground.Width(), rectClipBoxPlayground.Height(), 
        rectClipBoxBackBuffer.left, rectClipBoxBackBuffer.top, rectClipBoxBackBuffer.Width(), rectClipBoxBackBuffer.Height(), 
        _pBitmapRawBits, &_bitmapInfo, DIB_RGB_COLORS, SRCCOPY);

    _pMemDc->SelectObject(hMemBitmap); 

The problem is, the commented-out code of StretchBlt works flawlessly (except printing on some printers), but I can't use it because some printers have troubles with it. So I have to use StretchDIBits. Note that I firstly unselect the DIB from its memory dc temporarily, so that it is not associated with any dc. Then I use StretchDIBits but things just don't work! Output is messed up, like I give incorrect coordinates, areas are drawn off-set from where they should be drawn, and sometimes totally black. So I must be missing something (maybe something very trivial). Help! I tried changing signs of rectClipBoxBackBuffer.top and bitmapInfo.bmiHeader.biHeight, the results change, but nothing works like it should.

What am I doing wrong??