Advanced MFC Programming

Chapter 10. Bitmap
……
dwSize=bf.bfSize-sizeof(BITMAPFILEHEADER);
m_hDIB=::GlobalAlloc(GHND, dwSize);
ASSERT(m_hDIB);
lpDIB=(LPSTR)::GlobalLock(m_hDIB);
ASSERT(lpDIB);
Next, the DIB data is read into the global memory:
……
}
}
if(ar.Read(lpDIB, dwSize) != dwSize)
{
::GlobalUnlock(m_hDIB);
::GlobalFree(m_hDIB);
m_hDIB=NULL;
}
else ::GlobalUnlock(m_hDIB);
This completes reading the bitmap file. The DIB data is stored in m_hDIB now.
Creating DDB
On the view side, we need to display the bitmap stored in memory (whose handle is m_hDIB) instead of
the bitmap stored as resource. So we need to modify function CGDIView::OnInitialUpdate(), which will
be called whenever a new file is opened successfully. First, instead of obtaining data from the resource,
function CGDIDoc::GetHDib() is called to get the handle of DIB data:
void CGDIView::OnInitialUpdate()
{
CClientDC dc(this);
CGDIDoc *pDoc;
CBitmap *pBmp;
CPalette *pPalDraw;
LPBITMAPINFO lpBi;
LPLOGPALETTE lpLogPal;
CPalette *pPalOld;
int nSizeCT;
int i;
HBITMAP hBmp;
HGLOBAL hData;
CScrollView::OnInitialUpdate();
pDoc=GetDocument();
ASSERT_VALID(pDoc);
……
hData=pDoc->GetHDib();
Remember in the previous sample, after the DDB and palette are created, we will select them into the
memory DC so that the image can be drawn directly later. In this sample, when a new DIB file is opened,
there may be a bitmap (also a palette) that is being currently selected by the memory DC. If so, we need to
select it out of the memory DC, then lock the global memory and obtain its address that can be used to
access the DIB (In order to create DDB, we need the information contained in the DIB):
……
……
if(hData != NULL)
{
if(m_pPalMemOld != NULL)m_dcMem.SelectPalette(m_pPalMemOld, FALSE);
if(m_pBmpMemOld != NULL)m_dcMem.SelectObject(m_pBmpMemOld);
lpBi=(LPBITMAPINFO)::GlobalLock(hData);
ASSERT(lpBi);
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