很经典的实例，透明窗体

【核心代码】

BOOL CTransparentWindowDlg::OnInitDialog()
{
CDialog::OnInitDialog();

// Add "About..." menu item to system menu.

// IDM_ABOUTBOX must be in the system command range.
ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
ASSERT(IDM_ABOUTBOX < 0xF000);

CMenu* pSysMenu = GetSystemMenu(FALSE);
if (pSysMenu != NULL)
{
CString strAboutMenu;
strAboutMenu.LoadString(IDS_ABOUTBOX);
if (!strAboutMenu.IsEmpty())
{
pSysMenu->AppendMenu(MF_SEPARATOR);
pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
}
}

// Set the icon for this dialog.  The framework does this automatically
//  when the application's main window is not a dialog
SetIcon(m_hIcon, TRUE);	// Set big icon
SetIcon(m_hIcon, FALSE);	// Set small icon

// TODO: Add extra initialization here
SetupRegion();
return TRUE;  // return TRUE  unless you set the focus to a control
}

void CTransparentWindowDlg::OnSysCommand(UINT nID, LPARAM lParam)
{
if ((nID & 0xFFF0) == IDM_ABOUTBOX)
{
CAboutDlg dlgAbout;
dlgAbout.DoModal();
}
else
{
CDialog::OnSysCommand(nID, lParam);
}
}

// If you add a minimize button to your dialog, you will need the code below
//  to draw the icon.  For MFC applications using the document/view model,
//  this is automatically done for you by the framework.

void CTransparentWindowDlg::OnPaint() 
{
if (IsIconic())
{
CPaintDC dc(this); // device context for painting

SendMessage(WM_ICONERASEBKGND, (WPARAM) dc.GetSafeHdc(), 0);

// Center icon in client rectangle
int cxIcon = GetSystemMetrics(SM_CXICON);
int cyIcon = GetSystemMetrics(SM_CYICON);
CRect rect;
GetClientRect(&rect);
int x = (rect.Width() - cxIcon 1) / 2;
int y = (rect.Height() - cyIcon 1) / 2;

// Draw the icon
dc.DrawIcon(x, y, m_hIcon);
}
else
{
CDialog::OnPaint();
}
}

// The system calls this to obtain the cursor to display while the user drags
//  the minimized window.
HCURSOR CTransparentWindowDlg::OnQueryDragIcon()
{
return (HCURSOR) m_hIcon;
}

void CTransparentWindowDlg::SetupRegion()
{
CDC* pDC;
CDC	memDC;
CBitmap	cBitmap;
CBitmap* pOldMemBmp = NULL;
COLORREF col;
CRect cRect;
int	x, y;
CRgn wndRgn, rgnTemp;

pDC = GetDC();
GetWindowRect(&cRect);

//将模板位图选进设备场景中
cBitmap.LoadBitmap(IDB_MASK);
memDC.CreateCompatibleDC(pDC);
pOldMemBmp = memDC.SelectObject(&cBitmap);

//创建模板形状的不规则区域
wndRgn.CreateRectRgn(0, 0, cRect.Width(), cRect.Height());
for(x=0; x<=cRect.Width(); x )
{
for(y=0; y<=cRect.Height(); y )
{
//将位图中黑色小圆洞对应的区域抠掉
col = memDC.GetPixel(x, y);
if(col == 0)
{
rgnTemp.CreateRectRgn(x, y, x 1, y 1);
wndRgn.CombineRgn(&wndRgn, &rgnTemp, RGN_XOR);
rgnTemp.DeleteObject(); 
}
}
}
if (pOldMemBmp) memDC.SelectObject(pOldMemBmp);

//将不规则区域分配给窗体，也就是创建不规则的窗体
SetWindowRgn((HRGN)wndRgn, TRUE);
ReleaseDC(pDC);
}

BOOL CTransparentWindowDlg::OnEraseBkgnd(CDC* pDC) 
{ 
CRect	rect;
GetWindowRect(&rect);

CDC memDC;
CBitmap	cBitmap;
CBitmap*	pOldMemBmp = NULL;

//将背景位图加到设备场景中
cBitmap.LoadBitmap(IDB_BACK);
memDC.CreateCompatibleDC(pDC);
pOldMemBmp = memDC.SelectObject(&cBitmap);

//将背景位图显示出来
pDC->BitBlt(0, 0, rect.Width(), rect.Height(), &memDC, 0, 0, SRCCOPY);
if (pOldMemBmp) memDC.SelectObject( pOldMemBmp );

return TRUE;
//	return CDialog::OnEraseBkgnd(pDC);
}


UINT CTransparentWindowDlg::OnNcHitTest(CPoint point) 
{
UINT nHitTest = CDialog::OnNcHitTest(point); 

    return (nHitTest == HTCLIENT)? HTCAPTION:nHitTest;
}

void CTransparentWindowDlg::OnShowWindow(BOOL bShow, UINT nStatus) 
{
CDialog::OnShowWindow(bShow, nStatus);

//调整窗体大小，适应位图大小
CRect rc;
GetClientRect(&rc);
rc.right = rc.left 320;
rc.bottom = rc.top 150;
MoveWindow(&rc,TRUE);
}