Re: Application crashes on BitBlt after a while.. need help please

From:

"Giovanni Dicanio" <giovanni.dicanio@invalid.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Wed, 28 May 2008 12:20:10 +0200

Message-ID:

<eF153yKwIHA.5832@TK2MSFTNGP02.phx.gbl>

"vorange" <orangepic@yahoo.com> ha scritto nel messaggio
news:e5046e63-1541-4b7d-adbe-4fd964573170@26g2000hsk.googlegroups.com...

The debugger says it crashes on the statement BitBlt.
Apparently it is unable to get a handle to something (i think the DC)
when using BitBlt and fails an ASSERT.

[...]

void ScanDialog::OnPaint()
{
CPaintDC dc(this);

CDC dcMemory;
bool falsetrue = dcMemory.CreateCompatibleDC (&dc);
if(falsetrue == TRUE)
{
DrawCompass(IDC_AZIMUTH, &dcMemory);
}
}

Just for test, try using CMemDC class:

http://www.codeproject.com/KB/GDI/flickerfree.aspx

void ScanDialog::OnPaint()
{
  CPaintDC dc(this);
  DrawCompass( IDC_AZIMUTH, &dc );
}

void ScanDialog::DrawCompass( int id, CDC * dc )
{
   CMemDC dcMemory( dc );

    ... use dcMemory
}

The ASSERT on BitBlt DC seems strange to me, because you are doing a control
yourself here (if (dc2 != NULL ...):

       dc2 = pWndd->GetDC(); // dc is a CDC *dc2
if(dc2 != NULL)
{
         pWndd->GetClientRect(&rect); // rect is a CRect
         nX = rect.left;
         nY = rect.top;
         if(dc2->BitBlt(nX, nY, bmpInfo.bmWidth, bmpInfo.bmHeight,
dcMemory, 0, 0, SRCCOPY) != 0)

Giovanni