A line is drawn between two points, represented by the firstPoint field to the lastPoint field in the LineFigure class, as shown in the following image:

The header file overrides some of the methods of its DrawFigure base class. The DoubleClick method does nothing. As I see it, there is no really meaningful response to a double-click on a line. However, we still need to override the DoubleClick method, since it is a pure virtual method in the DrawFigure base class. If we do not override it, the LineFigure class will be abstract.

LineFigure.h

class LineFigure : public DrawFigure { 
  public: 
    LineFigure(const Window* windowPtr); 
    virtual FigureId GetId() const {return LineId;} 
    virtual void SetFirstPoint(Point point); 
 
    virtual bool IsClick(Point mousePoint); 
    virtual bool IsInside(Rect rectangleArea); 
    virtual void DoubleClick(Point mousePoint) {/* Empty. */} 
 
    virtual void Modify(Size distanceSize...