Advanced MFC Programming

Chapter 10. Bitmap
……
m_pBmpOld=m_dcMem.SelectObject(&m_bmpDraw);
m_pBmpMaskOld=m_dcMemMask.SelectObject(&m_bmpMask);
m_pBmpBSOld=m_dcMemBS.SelectObject(&m_bmpBS);
The mask and memory bitmaps must be created by calling function CBitmap::
CreateCompatibleBitmap(…), this will allow the created bitmaps to be compatible with the device context.
Next, the mask bitmap is generated from the normal bitmap image:
……
for(j=0; jbmiHeader.biHeight; j++)
{
for(i=0; ibmiHeader.biWidth; i++)
{
if(m_dcMem.GetPixel(i, j) == RGB(255, 255, 255))
{
m_dcMemMask.SetPixel(i, j, RGB(255, 255, 255));
}
else m_dcMemMask.SetPixel(i, j, RGB(0, 0, 0));
}
}
m_bBitmapLoaded=TRUE;
SetScrollSizes
(
MM_TEXT,
CSize(lpBi->bmiHeader.biWidth, lpBi->bmiHeader.biHeight)
);
::GlobalUnlock(hData);
if(nSizeCT != 0)dc.SelectPalette(pPalOld, FALSE);
}
Invalidate();
AfxGetApp()->DoWaitCursor(FALSE);
Every pixel of the normal image is examined to generate the mask image. Here functions
CDC::GetPixel(…) and CDC::SetPixel(…) are called for manipulating single pixels. Although the two
functions hide the details of device context and bitmap format, they are very slow, and should not be used
for fast bitmap drawing or image processing.
Drawing Bitmap with Transparancy
Function CGDIView::OnDraw(…) is modified as follows for drawing bitmap with transparency:
void CGDIView::OnDraw(CDC *pDC)
{
CPalette *pPal;
CPalette *pPalOld;
BITMAP bm;
if(m_bBitmapLoaded == FALSE)return;
CGDIDoc *pDoc=GetDocument();
ASSERT_VALID(pDoc);
pPal=pDoc->GetPalette();
pPalOld=pDC->SelectPalette(pPal, FALSE);
pDC->RealizePalette();
m_bmpDraw.GetBitmap(&bm);
m_dcMemBS.BitBlt
(
0,
0,
bm.bmWidth,
bm.bmHeight,
pDC,
0,
0,
321