Print Preview zoom problem

Peter T. O'Neill -- oneillpt@acadamh.ucd.ie
Thursday, November 14, 1996

Environment: VC++ 4.0, Win 95

I have a problem with zooming in print preview, if the document 
prints less than one full page. 

The printed output will be fine, print preview will initially be fine, 
but zooming give a blank page. 

If the document runs past one page, zooming in print preview works on 
the full pages, but again fails on the last, part full, page. If I 
keep in zoomed mode until I reach the last page, it will display in 
zoomed mode, but then display as blank when I return to normal mode. 

Any suggestions?
-----------------------------------------------------------------
Peter O'Neill, Mech. Eng. Dept., UCD, Belfield, Dublin 4, Ireland
Phone: +353-1-706 1889
Fax:   +353-1-283 0534
http://poneill.ucd.ie/

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Peter T. O'Neill -- oneillpt@acadamh.ucd.ie
Monday, November 25, 1996

> Date:          Thu, 14 Nov 1996 16:40:53 +0000 (GMT)
> From:          "Peter T. O'Neill" 
> Subject:       Print Preview zoom problem

> Environment: VC++ 4.0, Win 95
> 
> I have a problem with zooming in print preview, if the document 
> prints less than one full page. 
> 
> The printed output will be fine, print preview will initially be fine, 
> but zooming give a blank page. 
> 
> If the document runs past one page, zooming in print preview works on 
> the full pages, but again fails on the last, part full, page. If I 
> keep in zoomed mode until I reach the last page, it will display in 
> zoomed mode, but then display as blank when I return to normal mode. 
> 
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Followup information on fixing this problem from myself, as posted to 
microsoft.public.vc.mfc, where someone else posted the same problem: 
---------------------------------------------------------------------
patmac@suba.com wrote in article <328C7DCD.28A2@suba.com>...
> Here's an interesting problem, perhaps it makes sense to you.  The
> following is my OnDraw function for a CView derived view.  It works
> fine for text mode changing the font size on the fly is no problem. 
> But, when I do print preview it works fine for the initial display,
> but when the  button is pressed, the display goes to pot and
> never returns even when I zoom out.
> 
I have this problem also, and have found a fix (below) for my case.
Specifically, the displayed preview page goes blank when there is ONLY
ONE page to display, or when the page to be displayed is THE LAST OF A
NUMBER OF PAGES. If the page to be displayed is one of a number of
pages, but preceeds the last page, there is never a problem. In my
case, my view is derived from CListView, and prints a formatted
version of the displayed List control, with page header, WingDing font
characters replacing small icons for printing, and a few other
options. I must calculate the document length myself, in my OnPrint
function (OnDraw is not modified). I set a member variable BOOL
m_bPrintingComplete by comparing the y coordinate of the last line
overall with the y coordinate of the last line on the page just
printed (or presumably previewed), and use this in OnPrepareDC to set
CPrintInfo m_bContinuePrinting.

My problem is solved by making pInfo->m_bContinuePrinting TRUE
whenever OnPrepareDC is called in preview mode, as below. I have not
the time to work through the implementation of CPreviewView, but my
guess is that having m_bContinuePrinting set to FALSE in OnPrepareDC,
which is called for the zoomed page, prevents painting of the zoomed
page, even where it is the SAME page as has just been displayed
unzoomed. 
---------- 
void CFavWatchView2::OnPrepareDC(CDC* pDC, CPrintInfo* pInfo) {
 // TODO: Add your specialized code here and/or call the base class
 if (pInfo) 
 {
  if (m_bPrintingComplete) pInfo->m_bContinuePrinting = FALSE;
  else pInfo->m_bContinuePrinting = TRUE;
  //
  // fix single/last page problem here
  if (pInfo->m_bPreview) pInfo->m_bContinuePrinting = TRUE; 
  //
  pDC->SetMapMode( MM_TWIPS );
 }
 else CListView::OnPrepareDC(pDC, pInfo);
}
-----------------------------------------------------------------
Peter O'Neill, Mech. Eng. Dept., UCD, Belfield, Dublin 4, Ireland
Phone: +353-1-706 1889
Fax:   +353-1-283 0534
http://poneill.ucd.ie/

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