窗口透明

bool m_bTracking;   // 当鼠标被捕捉时设置为TRUE
HWND m_hCurrWnd;    // 鼠标所在窗口的句柄
HCURSOR m_hCursor;  // 棒型光标句柄
// 全局变量
typedef BOOL (WINAPI *lpfn) (HWND hWnd, COLORREF cr, BYTE bAlpha, DWORD dwFlags);
lpfn g_pSetLayeredWindowAttributes;

    HMODULE hUser32 = GetModuleHandle(_T("USER32.DLL"));
    g_pSetLayeredWindowAttributes = (lpfn)GetProcAddress(hUser32,
        "SetLayeredWindowAttributes");
    if (g_pSetLayeredWindowAttributes == NULL)
        AfxMessageBox (
        "Layering is not supported in this version of Windows",
        MB_ICONEXCLAMATION);
    
    // 装入棒形光标
    HINSTANCE hInstResource = AfxFindResourceHandle(
        MAKEINTRESOURCE(IDC_SIZEALL), RT_GROUP_CURSOR);
    m_hCursor = ::LoadCursor( NULL, MAKEINTRESOURCE(IDC_CROSS) );

void CLayeredWindowAttributesDlg::OnLButtonDown(UINT nFlags, CPoint point) 
{
    // TODO: Add your message handler code here and/or call default
       SetCapture();      //鼠标捕获设置到指定的窗口。在鼠标按钮按下的时候，这个窗口会为//当前应用程序或整个系统接收所有鼠标输入
       m_hCurrWnd = NULL; //现在还没有窗口透明
       m_bTracking = true;     // 设置track标志
        ::SetCursor(m_hCursor); // 将光标改为棒形    
    CDialog::OnLButtonDown(nFlags, point);
}

void CLayeredWindowAttributesDlg::OnMouseMove(UINT nFlags, CPoint point) 
{
    // TODO: Add your message handler code here and/or call default
    if (m_bTracking)
    {
       
            //  获取鼠标位置
            ClientToScreen(&point);
      
            // 获取鼠标下面所在的窗口句柄
            m_hCurrWnd = ::WindowFromPoint(point);
       
            // 显示该窗口的类、标题等信息…
            
    }
    CDialog::OnMouseMove(nFlags, point);
}

void CLayeredWindowAttributesDlg::OnLButtonUp(UINT nFlags, CPoint point) 
{
    // TODO: Add your message handler code here and/or call default
       //释放鼠标捕获
    ReleaseCapture();
    m_bTracking = false;
    //如果鼠标下面的窗口不是本程序WinTrans，我们就要设置层次样式并且通过设置滑动条来实现透明化。
    
    if (g_pSetLayeredWindowAttributes && m_hCurrWnd != m_hWnd)
    {
        ::SetWindowLong(m_hCurrWnd, GWL_EXSTYLE, GetWindowLong(m_hCurrWnd, 
            GWL_EXSTYLE) ^ /*WS_EX_LAYERED*/0x00080000);
        g_pSetLayeredWindowAttributes(m_hCurrWnd, 0,
    (BYTE)m_slider.GetPos(), /*LWA_ALPHA*/2);
        
        ::RedrawWindow(m_hCurrWnd, NULL, NULL,
            RDW_ERASE | RDW_INVALIDATE | 
            RDW_FRAME | RDW_ALLCHILDREN);
    }
    CDialog::OnLButtonUp(nFlags, point);
}