KISS(Keep It Simple, Standard)

void TransparentBlt(CDC *pDestDC, int nXDest, int nYDest, int nWidth, int nHeight, CBitmap * pBitmap, int nXsrc, int nYsrc, COLORREF clr)
{
 CDC maskDC, ImageDC;
 maskDC.CreateCompatibleDC(pDestDC);
 ImageDC.CreateCompatibleDC(pDestDC);

 CBitmap maskBMP;
 maskBMP.CreateBitmap(nWidth, nHeight, 1, 1, NULL);//創建單色掩碼位圖
 CBitmap *pOldBMP = ImageDC.SelectObject(pBitmap);
 CBitmap *maskOldBMP = maskDC.SelectObject(&maskBMP);
 
 ImageDC.SetBkColor(clr);// 設置透明色
 maskDC.BitBlt(0, 0, nWidth, nHeight, &ImageDC, nXsrc, nYsrc, SRCCOPY);

 //設置背景色為黑色，前景色為白色，將掩碼位圖與原位圖相"與"
 ImageDC.SetBkColor(RGB(0, 0, 0));
 ImageDC.SetTextColor(RGB(255, 255, 255));
 ImageDC.BitBlt(0, 0, nWidth, nHeight, &maskDC, nXsrc, nYsrc, SRCAND);

 //設置背景色為白色，前景色為黑色，將掩碼位圖與背景進行“與”運算
 pDestDC->SetBkColor(RGB(255, 255, 255));
 pDestDC->SetTextColor(RGB(0, 0, 0));
 pDestDC->BitBlt(nXDest, nYDest, nWidth, nHeight, &maskDC, nXsrc, nYsrc, SRCAND);
 // "或"運算,生成最終效果
 pDestDC->BitBlt(nXDest, nYDest, nWidth, nHeight, &ImageDC, nXsrc, nYsrc, SRCPAINT);

 if (pOldBMP) ImageDC.SelectObject(pOldBMP);
 ImageDC.DeleteDC();
 if (maskOldBMP) maskDC.SelectObject(maskOldBMP);
 maskDC.DeleteDC();
 if (maskBMP.m_hObject) maskBMP.DeleteObject();
}