January 27th, 2012, 03:41 AM
Unable to implement DIB printing with GDI (MFC)
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:
Variables with underscores are (private) member variables, declared like this:
// Prepare device context:
// Setup proper backbuffer:
_pMemDc = new CDC;
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);
Now below is what I do in my OnDraw override:
CDC *_pMemDc; // Backbuffer memory dc
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
Firstly I get the area to be drawn like this (simplified code):
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
rectClipBoxPlayground = _printingParams.pPrintInfo->m_rectDraw;
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:
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.
// Copy back buffer to screen/printer dc:
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);
What am I doing wrong??
Last edited by TX_; January 28th, 2012 at 01:15 PM.
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