private void StartDragging(object sender, MouseEventArgs e)
 {
     if (e.Button == MouseButtons.Left)
     {
         dragging     = true;
         pointClicked = new Point(e.X, e.Y);
     }
     else
     {
         dragging = false;
         DraggingEnd?.Invoke(this, e);
     }
 }
 private void StopDragging(object sender, MouseEventArgs e)
 {
     dragging = false;
     DraggingEnd?.Invoke(this, e);
 }