class EditField:....
{
....
public:
      void Paint(Draw& d)override{
           PaintSpinButtons();
           DoOriginalEditFieldPaintOnReducedSize();
      }
      void LeftDown(Point p, dword f)override{
           if(p not in SpinPart)
                Parent::LeftDown(p,f);
           else if(p in UpperPart of Spin)
                WhenSpin(false);
           else// (p in LowerPart of Spin)
                WhenSpin(true);
      }
      void LeftRepeat(Point p, dword f)override{
           LeftDown(p,f);
      }
      Image CursorImage(Point p, dword)override{
          // Image according to part of the Ctrl
      }
      //... maybe more to be override'd or rewrite to take care of Fake SpinButton part.

      Event<bool> WhenSpin;
private:
      bool with_spin : 1;
      bool spin_visible : 1;

      Size GetReducedSize(){
            Size sz=GetSize(); 
            if(with_spin && spin_visible)
                 reduce_size_to_leave_room_for_spin_buttons(sz);
     }
}