Vc++6.0MFC中使用鼠标画椭圆的实现过程

以下是在VC++6.0 MFC中使用鼠标画椭圆的实现过程：

1. 创建一个新的MFC应用程序项目。

2. 在资源视图中添加一个菜单资源，例如IDR_MAINFRAME。

3. 打开应用程序类的头文件，添加以下代码：

class CMyApp : public CWinApp
{
public:
    virtual BOOL InitInstance();
};

class CMyWnd : public CFrameWnd
{
public:
    CMyWnd();
protected:
    afx_msg void OnPaint();
    afx_msg void OnLButtonDown(UINT nFlags, CPoint point);
    afx_msg void OnLButtonUp(UINT nFlags, CPoint point);
    afx_msg void OnMouseMove(UINT nFlags, CPoint point);
    DECLARE_MESSAGE_MAP()
private:
    BOOL m_bDrawing;
    CRect m_rectEllipse;
};

BOOL CMyApp::InitInstance()
{
    m_pMainWnd = new CMyWnd;
    m_pMainWnd->ShowWindow(SW_SHOW);
    m_pMainWnd->UpdateWindow();
    return TRUE;
}

CMyWnd::CMyWnd()
{
    Create(NULL, _T("My Oval Drawing Program"));
    m_bDrawing = FALSE;
}

void CMyWnd::OnPaint()
{
    CPaintDC dc(this);
    if (m_bDrawing)
    {
        dc.SelectStockObject(NULL_BRUSH);
        dc.Ellipse(m_rectEllipse);
    }
}

void CMyWnd::OnLButtonDown(UINT nFlags, CPoint point)
{
    m_bDrawing = TRUE;
    m_rectEllipse.left = point.x;
    m_rectEllipse.top = point.y;
    m_rectEllipse.right = point.x;
    m_rectEllipse.bottom = point.y;
    SetCapture();
}

void CMyWnd::OnLButtonUp(UINT nFlags, CPoint point)
{
    m_bDrawing = FALSE;
    ReleaseCapture();
    Invalidate();
}

void CMyWnd::OnMouseMove(UINT nFlags, CPoint point)
{
    if (m_bDrawing)
    {
        CDC* pDC = GetDC();
        pDC->SelectStockObject(NULL_BRUSH);
        pDC->SetROP2(R2_NOTXORPEN);
        pDC->Ellipse(m_rectEllipse);
        m_rectEllipse.right = point.x;
        m_rectEllipse.bottom = point.y;
        pDC->Ellipse(m_rectEllipse);
        ReleaseDC(pDC);
    }
}

BEGIN_MESSAGE_MAP(CMyWnd, CFrameWnd)
    ON_WM_PAINT()
    ON_WM_LBUTTONDOWN()
    ON_WM_LBUTTONUP()
    ON_WM_MOUSEMOVE()
END_MESSAGE_MAP()

CMyApp theApp;

4. 编译并运行应用程序。当您单击菜单中的“画椭圆”按钮时，应用程序将允许您使用鼠标在窗口中绘制椭圆形。