MFC SDI（单文档）中创建一个新窗口（半透明）

思路来自：MFC Tutorial - Creating a window with two classes

在工程中新建一个类 CChildFrame

class CChildFrame : public CFrameWnd

在构造函数中：

CChildFrame::CChildFrame()
{
    Create(NULL,"MFC Tutorial Part 1 CoderSource Window");
}

可选：添加WM_PAINT消息：

void CChildFrame::OnPaint() 
{
    CPaintDC dc(this); // device context for painting
    
    // TODO: Add your message handler code here
    CDC *pDC = GetDC();

    CBrush brush(RGB(0, 0, 0));
    CBrush *pOldBrush = pDC->SelectObject(&brush);
    pDC->Rectangle(0, 0, 500, 500);
    pDC->SelectObject(pOldBrush);
    // Do not call CFrameWnd::OnPaint() for painting messages
}

在CXXApp类中，添加 CChildFrame 指针变量：

class CXXApp : public CWinApp
{
public:
    CChildFrame *m_pChildWnd;

        ...
}

在CXXApp类的 InitInstance 方法中添加：

BOOL CMultilayerDisplayApp::InitInstance()
{
    ...
    
    m_pChildWnd = new CChildFrame(); // 创建新窗口类对象
        //////// 这部分用于透明此窗口对象关联的窗口///////////
    //加入WS_EX_LAYERED扩展属性
    SetWindowLong(m_pChildWnd->m_hWnd, GWL_EXSTYLE, GetWindowLong(m_pChildWnd->m_hWnd, GWL_EXSTYLE)^0x80000);
    HINSTANCE hInst = LoadLibrary("User32.DLL");
    if (hInst)
    {
        typedef BOOL (WINAPI *MYFUNC)(HWND,COLORREF,BYTE,DWORD);
        MYFUNC fun = NULL;
        //取得SetLayeredWindowAttributes函数指针
        fun = (MYFUNC)GetProcAddress(hInst, "SetLayeredWindowAttributes");
        if (fun)
        {
            fun(m_pChildWnd->m_hWnd, 0, 128, 2);
        }
        FreeLibrary(hInst);
    }
        //////// 这部分用于透明此窗口对象关联的窗口///////////

    // The one and only window has been initialized, so show and update it.
    m_pMainWnd->ShowWindow(SW_SHOW);
    m_pMainWnd->UpdateWindow();

    m_pChildWnd->ShowWindow(SW_SHOW);
    m_pChildWnd->UpdateWindow();

    return TRUE;
}
                

效果如下：