在MFC++6.0中用鼠标选择圆心实现椭圆的扫描转换的代码

以下是在 MFC++6.0 中使用鼠标选择圆心实现椭圆的扫描转换的示例代码：

// MyEllipse.h 文件

class CMyEllipse : public CObject
{
public:
    CPoint m_Center;    // 圆心坐标
    int m_RadiusX;      // X半径
    int m_RadiusY;      // Y半径

    // 构造函数
    CMyEllipse(CPoint center = CPoint(0, 0), int radiusX = 0, int radiusY = 0);

    // 绘制椭圆
    void DrawEllipse(CDC* pDC);
};

// MyEllipse.cpp 文件

CMyEllipse::CMyEllipse(CPoint center, int radiusX, int radiusY)
{
    m_Center = center;
    m_RadiusX = radiusX;
    m_RadiusY = radiusY;
}

void CMyEllipse::DrawEllipse(CDC* pDC)
{
    // 计算椭圆上的点并绘制
    int x, y;
    float f;
    for (x = m_Center.x - m_RadiusX, y = m_Center.y, f = 0; x <= m_Center.x + m_RadiusX; x++, f += 1.0f)
    {
        y = (int)(m_Center.y + m_RadiusY * sqrt(1 - pow(f - m_Center.x + 0.5f, 2) / pow(m_RadiusX, 2)) + 0.5f);
        pDC->SetPixel(x, y, RGB(0, 0, 0));
        y = (int)(m_Center.y - m_RadiusY * sqrt(1 - pow(f - m_Center.x + 0.5f, 2) / pow(m_RadiusX, 2)) + 0.5f);
        pDC->SetPixel(x, y, RGB(0, 0, 0));
    }
    for (y = m_Center.y - m_RadiusY, x = m_Center.x, f = 0; y <= m_Center.y + m_RadiusY; y++, f += 1.0f)
    {
        x = (int)(m_Center.x + m_RadiusX * sqrt(1 - pow(f - m_Center.y + 0.5f, 2) / pow(m_RadiusY, 2)) + 0.5f);
        pDC->SetPixel(x, y, RGB(0, 0, 0));
        x = (int)(m_Center.x - m_RadiusX * sqrt(1 - pow(f - m_Center.y + 0.5f, 2) / pow(m_RadiusY, 2)) + 0.5f);
        pDC->SetPixel(x, y, RGB(0, 0, 0));
    }
}

// MyEllipseDlg.h 文件

class CMyEllipseDlg : public CDialog
{
public:
    CMyEllipse m_Ellipse;   // 椭圆
    BOOL m_bDrawing;        // 是否正在绘制
    CPoint m_StartPoint;    // 绘制起点
    CPoint m_EndPoint;      // 绘制终点

    // 构造函数
    CMyEllipseDlg(CWnd* pParent = NULL);

    // 对话框数据
    enum { IDD = IDD_MYELLIPSE_DIALOG };

protected:
    virtual void DoDataExchange(CDataExchange* pDX);    // DDX/DDV 支持

    // 消息映射
    afx_msg void OnPaint();
    afx_msg void OnLButtonDown(UINT nFlags, CPoint point);
    afx_msg void OnMouseMove(UINT nFlags, CPoint point);
    afx_msg void OnLButtonUp(UINT nFlags, CPoint point);
    DECLARE_MESSAGE_MAP()
};

// MyEllipseDlg.cpp 文件

CMyEllipseDlg::CMyEllipseDlg(CWnd* pParent /*=NULL*/)
    : CDialog(CMyEllipseDlg::IDD, pParent)
{
    m_bDrawing = FALSE;
}

void CMyEllipseDlg::DoDataExchange(CDataExchange* pDX)
{
    CDialog::DoDataExchange(pDX);
}

BEGIN_MESSAGE_MAP(CMyEllipseDlg, CDialog)
    ON_WM_PAINT()
    ON_WM_LBUTTONDOWN()
    ON_WM_MOUSEMOVE()
    ON_WM_LBUTTONUP()
END_MESSAGE_MAP()

void CMyEllipseDlg::OnPaint()
{
    CPaintDC dc(this);
    m_Ellipse.DrawEllipse(&dc);
}

void CMyEllipseDlg::OnLButtonDown(UINT nFlags, CPoint point)
{
    m_bDrawing = TRUE;
    m_StartPoint = point;
    m_EndPoint = point;
}

void CMyEllipseDlg::OnMouseMove(UINT nFlags, CPoint point)
{
    if (m_bDrawing)
    {
        CClientDC dc(this);
        dc.SetROP2(R2_NOT);
        dc.SelectStockObject(NULL_BRUSH);
        dc.Ellipse(m_StartPoint.x, m_StartPoint.y, m_EndPoint.x, m_EndPoint.y);
        m_EndPoint = point;
        dc.Ellipse(m_StartPoint.x, m_StartPoint.y, m_EndPoint.x, m_EndPoint.y);
    }
}

void CMyEllipseDlg::OnLButtonUp(UINT nFlags, CPoint point)
{
    m_bDrawing = FALSE;
    m_Ellipse.m_Center = CPoint((m_StartPoint.x + m_EndPoint.x) / 2, (m_StartPoint.y + m_EndPoint.y) / 2);
    m_Ellipse.m_RadiusX = abs(m_EndPoint.x - m_StartPoint.x) / 2;
    m_Ellipse.m_RadiusY = abs(m_EndPoint.y - m_StartPoint.y) / 2;
    Invalidate(FALSE);
}

// MyEllipse.rc 文件

IDD_MYELLIPSE_DIALOG DIALOGEX 0, 0, 200, 200
STYLE DS_SETFONT | DS_FIXEDSYS | WS_MINIMIZEBOX | WS_MAXIMIZEBOX | WS_POPUP | WS_VISIBLE | WS_CAPTION | WS_SYSMENU
EXSTYLE WS_EX_APPWINDOW
CAPTION "MyEllipse"
FONT 8, "MS Shell Dlg", 0, 0, 0x1
BEGIN
    CONTROL         "",IDC_STATIC,"Static",SS_BLACKFRAME,7,7,186,186
END

// MyEllipse.cpp 文件

#include "stdafx.h"
#include "MyEllipse.h"
#include "MyEllipseDlg.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

BEGIN_MESSAGE_MAP(CMyEllipseApp, CWinApp)
    ON_COMMAND(ID_HELP, &CWinApp::OnHelp)
END_MESSAGE_MAP()

CMyEllipseApp::CMyEllipseApp()
{
}

CMyEllipseApp theApp;

BOOL CMyEllipseApp::InitInstance()
{
    CWinApp::InitInstance();

    CMyEllipseDlg dlg;
    m_pMainWnd = &dlg;
    dlg.DoModal();

    return FALSE;
}

在上述代码中，我们定义了一个 `CMyEllipse` 类来表示椭圆，其中包括圆心坐标和 X、Y 半径。`DrawEllipse()` 方法用于计算椭圆上的点并绘制。

我们还定义了一个 `CMyEllipseDlg` 类作为主界面，并在界面上重写了鼠标事件以实现绘制椭圆的功能。当鼠标左键按下时，我们记录下起点并将 `m_bDrawing` 标志设置为 `TRUE`，表示正在绘制。当鼠标移动时，我们使用 `CClientDC` 对象绘制一个矩形来表示正在绘制的椭圆，并在移动过程中不断更新 `m_EndPoint` 坐标。当鼠标左键释放时，我们将 `m_bDrawing` 标志设置为 `FALSE`，然后计算出椭圆的圆心坐标和 X、Y 半径，最后绘制出整个椭圆。

最后，我们在 `MyEllipse.rc` 文件中定义了主界面的样式和布局，并在 `MyEllipse.cpp` 文件中启动了应用程序。