绘图基础--橡皮筋画线

// rubber.cpp  
  
#include <afxwin.h>  
  
// Define the application class  
class CApp : public CWinApp  
{  
public:  
    virtual BOOL InitInstance();  
};  
  
CApp App;    
  
// Define the window class  
class CWindow : public CFrameWnd  
{   
    HCURSOR cross;  
    HCURSOR arrow;  
    CPoint start, old;  
    BOOL started;  
public:  
    CWindow();   
    afx_msg void OnMouseMove(UINT,CPoint);  
    afx_msg void OnLButtonDown(UINT, CPoint);  
    afx_msg void OnLButtonUp(UINT, CPoint);  
    DECLARE_MESSAGE_MAP()  
};  
  
// The window constructor  
CWindow::CWindow()  
{   
    // Load two cursors  
    cross = AfxGetApp()->LoadStandardCursor(IDC_CROSS);  
    arrow = AfxGetApp()->LoadStandardCursor(IDC_ARROW);  
    started=FALSE;  
      
    // Create a custom window class  
    const char* pszWndClass = AfxRegisterWndClass(  
        CS_HREDRAW | CS_VREDRAW, NULL,  
        (HBRUSH)(COLOR_WINDOW+1), NULL);  
      
    // Create the window  
    Create(pszWndClass, "Drawing Tests",   
        WS_OVERLAPPEDWINDOW,  
        CRect(0,0,250,250));   
}  
  
// The message map  
BEGIN_MESSAGE_MAP( CWindow, CFrameWnd )  
    ON_WM_MOUSEMOVE()     
    ON_WM_LBUTTONDOWN()  
    ON_WM_LBUTTONUP()  
END_MESSAGE_MAP()  
  
// Start a new line when the user clicks  
// the mouse button down  
void CWindow::OnLButtonDown(UINT flag,  
    CPoint mousePos)  
{  
    started = TRUE;  
    ::SetCursor(cross);  
    // save the starting position of the line  
    start = old = mousePos;  
    CClientDC dc(this);  
    dc.SetROP2(R2_NOT);  
    dc.MoveTo(start);  
    dc.LineTo(old);  
}  
  
// Complete the line when the user releases  
// the mouse button  
void CWindow::OnLButtonUp(UINT flag,  
    CPoint mousePos)  
{  
    if (started)  
    {  
        started = FALSE;  
        ::SetCursor(arrow);  
        CClientDC dc(this);  
        dc.MoveTo(start);  
        dc.LineTo(old);  
    }  
}  
  
// Handle dragging  
void CWindow::OnMouseMove(UINT flag,  
    CPoint mousePos)  
{  
    // If the mouse button is down and there  
    // is a line in progress, rubber band  
    if ((flag == MK_LBUTTON) && started)  
    {  
        ::SetCursor(cross);  
        CClientDC dc(this);  
        dc.SetROP2(R2_NOT);  
        // Undraw the old line  
        dc.MoveTo(start);  
        dc.LineTo(old);  
        // Draw the new line  
        dc.MoveTo(start);  
        dc.LineTo(mousePos);  
        old=mousePos;  
    }  
    else  
        ::SetCursor(arrow);  
}  
  
// Init the application  
BOOL CApp::InitInstance()  
{  
    m_pMainWnd = new CWindow();  
    m_pMainWnd->ShowWindow(m_nCmdShow);  
    m_pMainWnd->UpdateWindow();  
    return TRUE;  
}