学步园

      在RGB模式下，alpha原理公式：displayColor = sourceColor × alpha / 255 + backgroundColor × (255 – alpha) / 255。

      假如不带alpha通道的自定义32位位图，如果不使用alpha通道，测计算结果是黑色的。因此只要保证最高8位为1即可，即

      newSourceColor = 0xff000000 | sourceColor ;

      下面是处理自定义位图透明过程函数：

void DrawBitmap(QPainter *pDC, int nLeft, int nTop,
        int width, int height,
        DWORD *bitmap, COLORREF clrBack)
{
        DWORD  dwLoopY = 0, dwLoopX = 0;
        COLORREF crPixel = 0;
        BYTE  byNewPixel = 0;
        int r, g, b;
       QRect rect(nLeft, nTop, width, height);
       QImage imgAlpha((const uchar *)bitmap, width, height, QImage::Format_ARGB32);
       r = GetRValue(clrBack);
       g = GetGValue(clrBack);
       b = GetBValue(clrBack);
 
       for (dwLoopY = 0; dwLoopY < height; dwLoopY++)
      {
            for (dwLoopX = 0; dwLoopX < width; dwLoopX++)
           {
                  QRgb rgb = imgAlpha.pixel(dwLoopX, dwLoopY);
                  QRgb rgbMask = qRgb(r, g, b);
                  if (rgb == rgbMask)
                 {
                        imgAlpha.setPixel(dwLoopX, dwLoopY, Qt::transparent);
                 }
           }
      }
       pDC->drawImage(rect, imgAlpha);
}