印第安人街头吹笛歌名:我重绘了对话框的标题栏、边框等。但有别的窗口在我对话框上面移动时，我重绘的对话框 刷新有点慢，有白色的残影。是怎么回事？

LRESULT OnNcPaint(WPARAM wParam, LPARAM lParam){  HDC hDC;            //窗口DC  HDC hSkinDC;        //皮肤DC  HBITMAP hOldBitmap; //旧的位图  int nSaveDC;        //保存DC  CRect rcWindow;     //窗口矩形  CRect rcClip;       //剪切矩形  CRect rcExclude;    //排除矩形(客户区的)  GetWindowRect(m_hWnd, &rcWindow);  GetClientRect(m_hWnd, &rcExclude);  ClientToScreen(m_hWnd, (LPPOINT)&rcExclude);  ClientToScreen(m_hWnd, (LPPOINT)&rcExclude+1);  hDC = GetDCEx(m_hWnd, NULL, DCX_WINDOW|0x00010000L); //0x00010000L这是微软一个没公开的标记  if( wp == 1 )  {     rcClip.SetRect(0, 0, rcWindow.Width(), rcWindow.Height();  }  else  {     HRGN hRgn = reinterpret_cast(wParam);     GetRgnBox(hRgn, &rcClip);     rcClip.OffsetRect(-rcWindow.TopLeft());  }    //偏移位置  rcExclude.OffsetRect(-rcWindow.TopLeft());  rcWindow.OffsetRect(-rcWindow.TopLeft());  //窗口皮肤DC  hSkinDC = CreateCompatibleDC(hDC);  hOldBitmap = (HBITMAP)SelectObject(hSkinDC, m_hSaveBitmap);  //m_hSaveBitmap是你在WM_SIZE里已画好的非客户区位图  //排除客户区  nSaveDC = SaveDC(hDC);  ExcludeClipRect(hDC, rcExclude.left, rcExclude.top, rcExclude.right, rcExclude.bottom);  //贴到屏上来  BitBlt(hDC, rcClip.left, rcClip.top, rcClip.Width(), rcClip.Height(), hSkinDC, rcClip.left, rcClip.top, SRCCOPY);  //释放资源   SelectObject(hSkinDC, hOldBitmap);   DeleteDC(hSkinDC);   RestoreDC(hDC, nSaveDC);   ReleaseDC(m_hWnd, hDC);return 0;}//这是保存位图,放到WM_SIZE里
LRESULT OnSize(WPARAM wParam, lParam)
{
    CRect rcWindow;
    GetWindowRect(m_hWnd, &rcWindow);
    SaveBitmap(rcWindow.Width(), rcWindow.Height());
    // 重窗口
    RedrawWindow(m_hWnd, NULL, NULL, RDW_ERASE|RDW_FRAME|RDW_INTERNALPAINT|RDW_INVALIDATE);
}

// 这里
BOOL SaveBitmap(int nWidth, int nHeight)
{
    if( nWidth == 0 || nHeight == 0 )
return FALSE;

    if( m_hSaveBitmap )
    {
DeleteObject(m_hSaveBitmap);
m_hSaveBitmap = NULL;
    }

    HDC hDC, hMemDC;
    HBITMAP hOldBitmap;
  

    hDC = GetDCEx(m_hWnd, NULL, DCX_CACHE); //获得高速缓存DC

    //窗口内存DC和保存位图
    hMemDC = CreateCompatibleDC(hDC);
    m_hSaveBitmap = CreateCompatibleBitmap(hDC, nWidth, nHeight);
    hOldBitmap = (HBITMAP)SelectObject(hMemDC, m_hSaveBitmap);

    //填充颜色
    SetRect(&rect, 0, 0, nWidth, nHeight);
    SetBkColor(hMemDC, RGB(255,255,255));
    ExtTextOut(hMemDC, 0, 0, ETO_OPAQUE, &rect, NULL, 0, NULL);


    /////////////////////////////////////////////////////////
    //下面你就可以在hMemDC上画出你窗口皮肤了,画出来的界面会保存在m_hSaveBitmap中,供WM_NCPAINT中使用

    //释放资源
    SelectObject(hMemDC, hOldBitmap);
    DeleteDC(hMemDC);
    ReleaseDC(m_hWnd, hDC);
}

这样有个好外就是只有当窗口大小发生变化时才绘制整窗口,否则它只会拿出以前保存的位画在屏幕上,这个可以极大的优化窗口重绘方式