void CtryBGDlg::SetupRegion( CDC *pDC, CBitmap &cBitmap, COLORREF TransColor ) 
{ 
  CDC memDC; 
  memDC.CreateCompatibleDC(pDC); 
  CBitmap *pOldMemBmp=NULL; 
  pOldMemBmp=memDC.SelectObject(&cBitmap); 
  BITMAP bit; 
  cBitmap.GetBitmap (&bit); 
  CRgn crRgn, crRgnTmp; 
  crRgn.CreateRectRgn(0, 0, 0, 0);//创建一个空区域 
  int iX = 0;int iY = 0; 
  for (iY = 0; iY < bit.bmHeight; iY++) 
  { 
    do 
    { 
      //skip over transparent pixels at start of lines. 
      while (iX <= bit.bmWidth && memDC.GetPixel(iX, iY) == TransColor) 
        iX++; 
      //remember this pixel 
      int iLeftX = iX; 
      //now find first non transparent pixel 
      while (iX <= bit.bmWidth && memDC.GetPixel(iX, iY) != TransColor) 
        ++iX; 
      //create a temp region on this info 
      crRgnTmp.CreateRectRgn(iLeftX, iY, iX, iY+1); 
      //combine into main region. 
      crRgn.CombineRgn(&crRgn, &crRgnTmp, RGN_XOR); 
      //delete the temp region for next pass (otherwise you'll get an ASSERT) 
      crRgnTmp.DeleteObject(); 
    }while(iX < bit.bmWidth); 
    iX = 0; 
  } 
  SetWindowRgn(crRgn, TRUE); 
  iX = (GetSystemMetrics(SM_CXSCREEN))-700; 
  iY = (GetSystemMetrics(SM_CYSCREEN)) / 2 - (bit.bmHeight / 2); 
  SetWindowPos(&wndTop, iX, iY, bit.bmWidth, bit.bmHeight, NULL);  
  // Free resources. 
  memDC.SelectObject(pOldMemBmp);
  // Put the original bitmap back (prevents memory leaks) 
  memDC.DeleteDC(); 
  crRgn.DeleteObject(); 
}

CBitmap bmp; 
bmp.LoadBitmapW(IDB_MASK); 
this->SetupRegion(this->GetWindowDC(),bmp,RGB(0,0,0));

BOOL CtryBGDlg::OnEraseBkgnd(CDC* pDC) 
{ 
  // TODO: 在此添加消息处理程序代码和/或调用默认值 
  CRect rect; 
  this->GetWindowRect(&rect); 
  CDC memDC; 
  CBitmap bmp; 
  CBitmap *pOldBmp=NULL; 
  bmp.LoadBitmapW(IDB_INTERFACE); 
  memDC.CreateCompatibleDC(pDC); 
  pOldBmp=memDC.SelectObject(&bmp); 
  pDC->BitBlt(0,0,rect.Width(),rect.Height(),&memDC,0,0,SRCCOPY); 
  if(pOldBmp) 
  { 
    memDC.SelectObject(pOldBmp); 
  } 
  return true; 
// return CDialog::OnEraseBkgnd(pDC); 
}

LRESULT CtryBGDlg::OnNcHitTest(CPoint point) 
{ 
  // TODO: 在此添加消息处理程序代码和/或调用默认值 
  CRect rc; 
  GetClientRect(&rc); 
  ClientToScreen(&rc); 
  return rc.PtInRect(point) ? HTCAPTION : CDialog::OnNcHitTest(point); 
// return CDialog::OnNcHitTest(point); 
}

CRgn crRgn, crRgnTmp; 
  //创建一个空区域 
  crRgn.CreateRectRgn(0, 0, 0, 0); 
  int iX = 0;int iY = 0; 
  for (iY = 0; iY < bit.bmHeight; iY++) 
  { 
    do 
    { 
      //skip over transparent pixels at start of lines. 
      //以一个相素列为单位，找到在这一个相素列中，第一个不是要设为透明相素的点iX。 
      //然后再找到以这个iX为起点的，在这个一个相素列中最后跟他临近的最后一个不是透明的点。 
      //然后将他们一起合并到crRgn中。 
      while (iX <= bit.bmWidth && memDC.GetPixel(iX, iY) == TransColor) 
        iX++;//在iY和iY+1这个相索列中，第一个不设为透明的点的X坐标 
      int iLeftX = iX;//保存这个点的坐标 
      while (iX <= bit.bmWidth && memDC.GetPixel(iX, iY) != TransColor) 
        ++iX;//这是找到在iX最临近的不透明的X坐标 
      crRgnTmp.CreateRectRgn(iLeftX, iY, iX, iY+1);//这四个点连在一起就是现在刚找到的不透明的区域 
      //合并区域 
      crRgn.CombineRgn(&crRgn, &crRgnTmp, RGN_OR); 
      //记得最终要手动删除crRgnTmp对象 
      crRgnTmp.DeleteObject(); 
    }while(iX < bit.bmWidth);
    //如果iX没有达到图片的末尾，说明还没有枚举完这一行，则在iY和iY+1这个行上，进行下一轮的//枚举 
    iX = 0; 
}