OpenTween.TweenMain.ListTab_MouseMove C# (CSharp) Method

        private void ListTab_MouseMove(object sender, MouseEventArgs e)
        {
            //タブのD&D

            if (!this._cfgCommon.TabMouseLock && e.Button == MouseButtons.Left && _tabDrag)
            {
                string tn = "";
                Rectangle dragEnableRectangle = new Rectangle(_tabMouseDownPoint.X - (SystemInformation.DragSize.Width / 2), _tabMouseDownPoint.Y - (SystemInformation.DragSize.Height / 2), SystemInformation.DragSize.Width, SystemInformation.DragSize.Height);
                if (!dragEnableRectangle.Contains(e.Location))
                {
                    //タブが多段の場合にはMouseDownの前の段階で選択されたタブの段が変わっているので、このタイミングでカーソルの位置からタブを判定出来ない。
                    tn = ListTab.SelectedTab.Text;
                }

                if (string.IsNullOrEmpty(tn)) return;

                foreach (TabPage tb in ListTab.TabPages)
                {
                    if (tb.Text == tn)
                    {
                        ListTab.DoDragDrop(tb, DragDropEffects.All);
                        break;
                    }
                }
            }
            else
            {
                _tabDrag = false;
            }

            Point cpos = new Point(e.X, e.Y);
            for (int i = 0; i < ListTab.TabPages.Count; i++)
            {
                Rectangle rect = ListTab.GetTabRect(i);
                if (rect.Left <= cpos.X & cpos.X <= rect.Right &
                   rect.Top <= cpos.Y & cpos.Y <= rect.Bottom)
                {
                    _rclickTabName = ListTab.TabPages[i].Text;
                    break;
                }
            }
        }