/// <summary> Close form. May not close if FormClosing denies it </summary>
        public void Close()
        {
            GLHandledArgs e = new GLHandledArgs();

            OnClose(e);
            if (!e.Handled)
            {
                OnClosed();
                Remove(this);
            }
        }
 /// <summary> Called on close request. Override if required in derived classes </summary>
 public virtual void OnClose(GLHandledArgs e)
 {
     FormClosing?.Invoke(this, e);
 }