CDC::AlphaBlend
Visual Studio 2012
Call this member function to display bitmaps that have transparent or semitransparent pixels.
BOOL AlphaBlend( int xDest, int yDest, int nDestWidth, int nDestHeight, CDC* pSrcDC, int xSrc, int ySrc, int nSrcWidth, int nSrcHeight, BLENDFUNCTION blend );
See AlphaBlend in the Windows SDK for more information.