MFC实现鼠标跟踪画直线

#include <afxwin.h>
class CMyApp:public CWinApp{
public:
	virtual BOOL InitInstance();
};
class CMainWindow:public CFrameWnd{
protected:
	BOOL m_bTracking;
	BOOL m_bCaptureEnabled;
	CPoint m_ptFrom;
	CPoint m_ptTo;
    
	void InvertLine(CDC* pDC,CPoint ptFrom,CPoint ptTo);
public:
	CMainWindow();
protected:
	afx_msg void OnLButtonDown(UINT nFlags,CPoint point);
	afx_msg void OnLButtonUp(UINT nFlags,CPoint point);
	afx_msg void OnMouseMove(UINT nFlags,CPoint point);
	afx_msg void OnNcLButtonDown(UINT nHitTest,CPoint point); 
	DECLARE_MESSAGE_MAP()
};
#include"MouseCap.h"
CMyApp myApp;
BOOL CMyApp::InitInstance(){
m_pMainWnd = new CMainWindow;
m_pMainWnd->ShowWindow(m_nCmdShow);
m_pMainWnd->UpdateWindow();
return TRUE;
}
BEGIN_MESSAGE_MAP(CMainWindow,CFrameWnd)
	ON_WM_LBUTTONDOWN()
	ON_WM_LBUTTONUP()
	ON_WM_MOUSEMOVE()
	ON_WM_NCLBUTTONDOWN()
END_MESSAGE_MAP()
CMainWindow::CMainWindow(){
m_bTracking = FALSE;
m_bCaptureEnabled = TRUE;
CString strWndClass = AfxRegisterWndClass(
	0,
	AfxGetApp()->LoadStandardCursor(IDC_CROSS),//鼠标样式变为十字
	(HBRUSH)(COLOR_WINDOW+1),
	AfxGetApp()->LoadStandardIcon(IDI_WINLOGO)
	);
Create(strWndClass,_T("Mouse capture demo(Capture Enabled)"));
}
void CMainWindow::OnLButtonDown(UINT nFlags,CPoint point){
	m_ptFrom = point;//当鼠标按下时记录鼠标位置
	m_ptTo = point;
	m_bTracking = TRUE;
	if(m_bCaptureEnabled)
		SetCapture();
}
void CMainWindow::OnMouseMove(UINT nFlags,CPoint point){
	if(m_bTracking){
	CClientDC dc(this);
	InvertLine(&dc,m_ptFrom,m_ptTo);
	InvertLine(&dc,m_ptFrom,point);
	m_ptTo = point;
	}
}
void CMainWindow::OnLButtonUp(UINT nFlags,CPoint point){
	if(m_bTracking){
	m_bTracking = false;
	if(GetCapture()==this)
		::ReleaseCapture();
	CClientDC dc(this);
	InvertLine(&dc,m_ptFrom,m_ptTo);
	CPen pen(PS_SOLID,16,RGB(255,0,0));
	dc.SelectObject(&pen);
	dc.MoveTo(m_ptFrom);
	dc.LineTo(point);
	}
}
void CMainWindow::OnNcLButtonDown(UINT nHitTest,CPoint point){
	if(nHitTest == HTCAPTION){
		m_bCaptureEnabled = m_bCaptureEnabled?FALSE:TRUE;
		SetWindowText(m_bCaptureEnabled?
			_T("Mouse capture demo(Capture Enabled)"):_T("Mouse capture demo(Capture Disabled)"));
	}
	CFrameWnd::OnNcLButtonDown(nHitTest,point);
}
void CMainWindow::InvertLine(CDC* pDC,CPoint ptFrom,CPoint ptTo){
	int nOldMode=pDC->SetROP2(R2_NOT);
	pDC->MoveTo(ptFrom);
	pDC->LineTo(ptTo);
	pDC->SetROP2(nOldMode);
}