Question

I’m using MFC’s doc/view architecture to implement printing. I use double buffering, I draw everything onto my backbuffer which is DIB bitmap. Than I use StretchBlt to copy that DIB onto printer DC.

The strange thing is – print preview is working well! When I print on virtual PDF printer, it is working well! But when I print on actual printer (I’m testing on two different printers – same results) – it just prints “garbage”. The “garbage” means sometimes it prints totally black page, sometimes it prints the first few pages repeatedly, i.e. it prints wrong part of DIB, just like if I messed up coordinates to StretchBlt, but I didn’t mess anything up, I checked multiple times, plus why is print preview is working flawlessly then?

I tried many variations:

1. Using memory DC compatible to screen DC, when printing.
2. Using memory DC compatible to printer DC, and selecting my DIB into it.
3. Using memory DC compatible to printer DC, and using dedicated DIB onto which I copy my original backbuffer DIB.
   etc.

But the results are same. Below is the code where i create the DIB. I think the DIB format might be the problem, so please advice if there is something wrong with it. I tried both 24 bits and 32 bits as values for bmiHeader.biBitCount.

// Setup proper backbuffer:

_CleanupBackBufferStuff();

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

BITMAPINFO bmi;
memset(&bmi, 0, sizeof(BITMAPINFO));
bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
bmi.bmiHeader.biWidth = _sizeBackBuffer.cx;
bmi.bmiHeader.biHeight = -_sizeBackBuffer.cy; // top-down
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biBitCount = 24; // Tried 32 as well
bmi.bmiHeader.biCompression = BI_RGB;

unsigned char *pBitmapRawBits = 0;

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

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

Also here is the code for StretchBlt (nothing special here):

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

BOOL bSuccess = pDC->StretchBlt(rectClipBoxPlayground.left, rectClipBoxPlayground.top, rectClipBoxPlayground.Width(), rectClipBoxPlayground.Height(), 
        _pMemDc, rectClipBoxBackBuffer.left, rectClipBoxBackBuffer.top, rectClipBoxBackBuffer.Width(), rectClipBoxBackBuffer.Height(), SRCCOPY);

StretchBlt returns true, also (pDC->GetDeviceCaps(RASTERCAPS) & RC_STRETCHBLT) is true as well.

UPDATE: After Adrian’s comment, I changed my code to use StretchDIBits. The problem is still the same! Below is the code I’m using currently:

// Copy back buffer to screen dc:

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

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

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

_pMemDc->SelectObject(hMemBitmap);

It still behaives like the source coordinates are incorrect. It either prints one of first few pages (no matter what page I select), or prints almost-fully-black pages. The print preview is working perfectly, so this makes me think there should be no problems with my coordinate-calculation code. It works in preview, it works with virtual (pdf) printer, it fails when printing on actual printer. What the hell?….

Answer 1

Make sure you don’t have the DIBSECTION selected into more than one DC at a time. That can cause all sorts of unpredictable behavior.

For printing, you can probably bypass the memory DC altogether if you keep your bmi and pBitmapRawBits handy. Make sure the DIBSECTION is not selected into any DC, and then call SetDIBitsToDevice or StretchDIBits to transfer the image to the printer DC.

If you’re still having problems, you might want to check the capabilities of your printers. Not all the drivers support all the bitmap transfer methods. I believe the printing system is supposed to hide those differences from you, but perhaps not. Call GetDeviceCaps on your printer DC, and check the RASTERCAPS for RC_BITBLT and friends.