运行效果：

关键代码：

新增头文件：

//item_cruciform.hpp
#ifndef ITEM_CRUCIFORM_HPP_INCLUDED
#define ITEM_CRUCIFORM_HPP_INCLUDED

#include <cmath>
#include "item_line.hpp"

class CruciformItem : public IItem
{
public:
    CruciformItem()
        : _startPosition(0, 0), _endPosition(0, 0)
    {

    }

    virtual void SetForegroundColor(wxColor const& color)
    {
        _hor_line.SetForegroundColor(color);
        _ver_line.SetForegroundColor(color);
    }

    virtual wxColor const& GetForegroundColor() const
    {
        return _hor_line.GetForegroundColor();
    }

    void Draw(wxDC& dc) const;
    //在鼠标按下函数中调用，所以鼠标按下的点即为_startPosition
    virtual void OnDrawStart(wxPoint const& point)
    {
        _startPosition = point;
    }

    virtual void OnDrawEnd(wxPoint const& point);

private:
    LineItem _hor_line, _ver_line;

    wxPoint _startPosition, _endPosition;
};

#endif // ITEM_CRUCIFORM_HPP_INCLUDED

新增源文件：

//item_cruciform.cpp
#include "item_cruciform.hpp"

void CruciformItem::OnDrawEnd(wxPoint const& point)
{//在鼠标移动和抬起时调用，所以鼠标抬起时的点即为_endPosition
    _endPosition = point;
    //重新调整水平线和垂直线的起点和终点
    int dx = std::abs(_endPosition.x - _startPosition.x);//两点水平距离
    _hor_line.OnDrawStart(wxPoint(_startPosition.x - dx, _startPosition.y));
    _hor_line.OnDrawEnd(wxPoint(_startPosition.x + dx, _startPosition.y));

    int dy = std::abs(_endPosition.y - _startPosition.y);
    _ver_line.OnDrawStart(wxPoint(_startPosition.x, _startPosition.y - dy));
    _ver_line.OnDrawEnd(wxPoint(_startPosition.x, _startPosition.y + dy));
}

void CruciformItem::Draw(wxDC& dc) const
{
    _hor_line.Draw(dc);
    _ver_line.Draw(dc);
}

新增“十字形”菜单项

注意：菜单项类型是Radio，否则不能被选中

新增创建十字形的代码：