Re: CDC does not Work Properly

"David Ching" <>
Wed, 30 Jan 2008 04:54:07 -0800
"Matrixinline" <> wrote in message

In a Dialog based application I have OnPaint method like this

CDC *pDC = GetDC();
               CDC oTempDC;

oTempDC.BitBlt (0, 0, screenMaxX, screenMaxY, m_pProcDC, 0, 0,
// m_pProcDC is CDC and contains a Bitmap as selected object
oTempDC.DrawIcon(oRect.left,, m_hIcon);
// Loaded ICON from resource m_hIcon
pDC->BitBlt(0, 0, screenMaxX, screenMaxY,&oTempDC, 0, 0, SRCCOPY);

it diaplays Nothing!! id displays only the background color of dialog
nothing else.
If I replace the code

CDC *pDC = GetDC();
               // m_pProcDC is CDC and contains a Bitmap as selected
pDC->BitBlt(0, 0, screenMaxX, screenMaxY,m_pProcDC, 0, 0, SRCCOPY);
it works!!

Can you please let me know why it is displaying anything?

First, in OnPaint(), you aren't supposed to use GetDC()/ReleaseDC(). You're
supposed to use CPaintDC instead (when you add the OnPaint() handler, the
handler should have this code in it already):

void CMyDlg::OnPaint()
  CPaintDC dc(this); // device context for painting

Make sure coordinates are correct for BitBlt(). Unfortunately, seeing
what's in the mem DC is hard... someone should make Intellisense for DC's!

-- David

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