绘制透明背景位图

// when blitting from a monochrome DC to a color DC, 

// the color black in the source turns into the destination's text color, 

// and the color white in the source turns into the destination's background color. 

// If you blit from a color DC to a monochrome DC, 

// then all pixels in the source that are equal to the background color will turn white, and all other pixels will turn black. 

// In other words, GDI considers a monochrome bitmap to be black pixels on a white background. 

static void DrawTransBmp( HDC hDst, HBITMAP hImg, COLORREF clrTran )

{

    COLORREF colorOldFront;

    COLORREF colorOldBg;



    BITMAP bmp;

    GetObject( hImg, sizeof( bmp ), &bmp );



    HDC hForeDC = ::CreateCompatibleDC( hDst );

	::SelectObject ( hForeDC, hImg );



    //prepare mask dc

    HDC hDCMask = CreateCompatibleDC ( hDst );

    // MSDN:    When a memory device context is created, it initially has a 1-by-1 monochrome bitmap selected into it.

    //          If this memory device context is used in CreateCompatibleBitmap, the bitmap that is created is a monochrome bitmap. 

    HBITMAP hBmpMask = CreateCompatibleBitmap( hDCMask, bmp.bmWidth, bmp.bmHeight );

	::SelectObject ( hDCMask, hBmpMask );

    ::SetBkColor( hForeDC, clrTran );                                                //Set clrTran as blackground color

    ::BitBlt( hDCMask, 0, 0, bmp.bmWidth, bmp.bmHeight, hForeDC, 0, 0, SRCCOPY );    //monochrome, background color is white



    //mask the foreground 

    ::SetBkColor( hForeDC, RGB(0,0,0) );

    ::SetTextColor( hForeDC, RGB(255,255,255) );

	::BitBlt( hForeDC, 0, 0, bmp.bmWidth, bmp.bmHeight, hDCMask, 0, 0, SRCAND );



    //mask the background

    colorOldBg = ::SetBkColor( hDst, RGB(255,255,255) );

    colorOldFront = ::SetTextColor( hDst, RGB(0,0,0) );

	::BitBlt( hDst, 0, 0, bmp.bmWidth, bmp.bmHeight, hDCMask, 0, 0, SRCAND ); 



    //or foreground and background

	::BitBlt( hDst, 0, 0, bmp.bmWidth, bmp.bmHeight, hForeDC, 0, 0, SRCPAINT );



    //recover hDst color of background and foreground

    ::SetBkColor( hDst, colorOldBg );

    ::SetTextColor( hDst, colorOldFront );



    //release object

    ::DeleteDC( hDCMask );

    ::DeleteDC( hForeDC );

    ::DeleteObject( hBmpMask );

}