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：