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 );
}