Get Ready to Unleash the Power of UCanCode .NET

Code Snippet

// the blending of the bitmap is quite simple
// (in the OnPaint() method or the WM_PAINT message handler: 
BITMAP bm;
GetObject(background, sizeof(BITMAP), &bm);
AlphaBlend(hdcMemWork, 0,0, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, 
           bm.bmWidth, bm.bmHeight, blendFkt)
SelectObject(hdcMem, hbmOld);

// The tricky thing is to pre multiply the alpha channel
// values after loading the 32 bit bitmaps
if(bmInfo.bmiHeader.biBitCount == 32 )
// Alpha Channel
{
    // pre-multiply rgb channels with alpha channel
    for (int y=0; y<bmInfo.bmiHeader.biHeight; ++y)
    {
        BYTE *pPixel= (BYTE *) lpDIBBits + bmInfo.bmiHeader.biWidth * 4 * y;
        for (int x=0; x<bmInfo.bmiHeader.biWidth ; ++x)
        {
            pPixel[0]= pPixel[0]*pPixel[3]/255;
            pPixel[1]= pPixel[1]*pPixel[3]/255;
            pPixel[2]= pPixel[2]*pPixel[3]/255;
            pPixel+= 4;
        }
    }
}