Scanning of screen pixels works in debug mode but not in release mode.

[DonDilworth]

Here's my code:

BitmapClip.Attach(HBitmapClip);
BitmapClip.GetObject( sizeof (BITMAP), &BitmapClipInfo );
MemDC.CreateCompatibleDC( m_paintDC );
MemDC.SelectObject( &BitmapClip);
xx = BitmapClipInfo.bmWidth;
yy = BitmapClipInfo.bmHeight;
if ( xx > m_HSize ) xx = m_HSize;
if ( yy > m_VSize ) yy = m_VSize;

HDC hd;
hd = (HDC) dc;

BitBlt
( hd,
ix,
iy,
xx,
yy,
MemDC,
0,
0,
SRCCOPY );

::CloseClipboard();
m_textflag = 2;
CString text;

showprogressbar();
for ( y = 0; y < 400; y++ ) { // scan photo here

progress = y/4;
updateprogressbar( progress );
if ( checkstopsign() ) {
InvalidateRect( &m_DWGarea );
killprogressbar();
wndout("Scan aborted \r\n");
return;
}
for ( x = 0; x < 400; x++ ) {
xx = x * m_nFfactX * xfudge + m_nXoffSet;
yy = y * m_nFfactY * yfudge + m_nYoffSet;
clr = dc.GetPixel( xx, yy );
if ( clr == CLR_INVALID ) clr = RGB(0,0,0);

m_mapRGB[x][y] = clr; // use all three colors in map only for photo

}
}
killprogressbar();

I put a graphics picture on the clipboard, and this code copies it to a dialog window. Then it samples that window, loading the array m_mapRGB[][] with each of 400 x 400 pixels. Later, I process this picture.

In debug mode, this works perfectly. In release mode, the loop on y gets about 1/3 of the way through, and then the dialog vanishes. I can display the dialog again with a keystroke, but the sampled array is blank below the 1/3 point. If I start the sampling loop again, it works as it should, and the whole picture is sampled. What is going on?

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