Draw a Transparent Bitmap into the destination DC with Pallete in MFC

// Draw a transparent bitmap into the destination DC with Pallete

void CEMCHotCtrl::TransparentBlt(HDC hdcDest, int nXDest, int nYDest, int nWidth, int nHeight, HBITMAP hBitmap, int nXSrc, int nYSrc, COLORREF colorTransparent, HPALETTE hPal)

{

CDC dc, memDC, maskDC, tempDC;

dc.Attach( hdcDest );

maskDC.CreateCompatibleDC(&dc);

CBitmap maskBitmap;

// These store return of SelectObject() calls

CBitmap* pOldMemBmp = NULL;

CBitmap* pOldMaskBmp = NULL;

HBITMAP hOldTempBmp = NULL;

memDC.CreateCompatibleDC (&dc);

tempDC.CreateCompatibleDC (&dc);

CBitmap bmpImage;

bmpImage.CreateCompatibleBitmap (&dc, nWidth, nHeight);

pOldMemBmp = memDC.SelectObject (&bmpImage);

// Select and realize the palette

if (dc.GetDeviceCaps (RASTERCAPS) & RC_PALETTE && hPal)

{

::SelectPalette( dc, hPal, FALSE );

dc.RealizePalette();

::SelectPalette( memDC, hPal, FALSE );

}

hOldTempBmp = (HBITMAP) ::SelectObject (tempDC.m_hDC, hBitmap);

memDC.BitBlt (0, 0, nWidth, nHeight, &tempDC, nXSrc, nYSrc, SRCCOPY);

// Create monochrome bitmap for the mask

maskBitmap.CreateBitmap (nWidth, nHeight, 1, 1, NULL);

pOldMaskBmp = maskDC.SelectObject (&maskBitmap);

memDC.SetBkColor (colorTransparent);

// Create the mask from the memory DC

maskDC.BitBlt (0, 0, nWidth, nHeight, &memDC, 0, 0, SRCCOPY);

// Set the background in memDC to black. Using SRCPAINT with black and any other color results in the other color, thus making black the transparent color

memDC.SetBkColor (RGB (0,0,0));

memDC.SetTextColor (RGB (255,255,255));

memDC.BitBlt (0, 0, nWidth, nHeight, &maskDC, 0, 0, SRCAND);

// Set the foreground to black. See comment above.

dc.SetBkColor (RGB (255,255,255));

dc.SetTextColor (RGB (0,0,0));

dc.BitBlt (nXDest, nYDest, nWidth, nHeight, &maskDC, 0, 0, SRCAND);

// Combine the foreground with the background

dc.BitBlt (nXDest, nYDest, nWidth, nHeight, &memDC, 0, 0, SRCPAINT);

if (hOldTempBmp)

::SelectObject (tempDC.m_hDC, hOldTempBmp);

if (pOldMaskBmp)

maskDC.SelectObject (pOldMaskBmp);

if (pOldMemBmp)

memDC.SelectObject (pOldMemBmp);

dc.Detach();

}