Advanced MFC Programming

Chapter 12. Screen Capturing & Printing
12.5 Printing on Separate Pages
If we want to output an image on separate papers, there are two situations: 1) Number of required
pages is known before the printing starts. 2) Number of required pages has to be decided after the printing
starts. For different situations, we need to use different approaches.
Number of required Pages is Known Beforehand
Sample 12.5-1\GDI is based on sample 12.4\GDI and demonstrates how to implement printing when
the total number of pages is known beforehand.
For some applications, the number of required pages for printing is fixed. For this situation, we need to
override function CView::OnPreparePrinting(…), and call function CPrintInfo::SetMaxPage(…) to set
the page range. By doing this, when the printing is being processed, function CView:OnPrint(…) will be
called repeatedly until all the pages are printed out. Within CView::OnPrint(…), the page information can
be obtained from member CPrintInfo::m_nCurPage (The second parameter of this function is a pointer to
class CPrintInfo), which stands for the current page number that is being printed. According to this
number, we can output different contents to different pages. The printing will be stopped after all the pages
are printed out.
For example, suppose whenever we want to print out the captured image, we’d like to make two
copies, one with 100% ratio and one with 200% ratio. In this case the number of pages is determined
beforehand. Before the printing begins, we can set the number of pages in function
CGDIView::OnPreparePrinting(…) as follows:
BOOL CGDIView::OnPreparePrinting(CPrintInfo *pInfo)
{
pInfo->SetMaxPage(2);
return DoPreparePrinting(pInfo);
}
By doing this, if the user executes printing command, in the popped up dialog box, the total number of
pages will be set to 2. The user can choose to print any of the pages or both of them. In function
CGDIView::OnPrint(…), we need to check which page is being printed and call function
::StretchDIBits(…) using the corresponding ratio:
……
……
……
nRatio=pInfo->m_nCurPage;
::StretchDIBits
(
pDC->GetSafeHdc(),
0,
0,
nRatio*lpBi->bmiHeader.biWidth,
-nRatio*lpBi->bmiHeader.biHeight,
0,
Setting Number of Pages Just Before Printing Starts
However this is not a normal case. Because the user can actually change the printing ratio, the number
of pages actually needed depends on print settings. For example, when the user set the printing ratio to
400%, the image that can originally fit into one page (when the ratio is 100%) often requires more than one
page now. So the actual number of pages needed depends on the printing ratio, which can range from 25%
to 400%.
One solution to this problem is to calculate the actual number of pages just before the printing starts.
At this time, the print setting will not be changed any more, so we can calculate the number of required
pages and call function CPrintInfo::SetMaxPage(…) to set the page range.
This can be done in either function CView::BeginPrinting(…) or in function CView::
OnPrepareDC(…). The first function will be called just before the print job begins, and the second function
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