dc.LineTo(right,top); //從(left,top)點至(right,top)點，畫壹條直線
下面是畫壹個矩形
dc.MoveTo(left,top);
dc.LineTo(right,top); //畫上邊線，(left,top)點至(right,top)點
dc.LineTo(right,bottom);//畫右邊線，(right,top)點至(right,bottom)點
dc.LineTo(left,bottom);//畫下邊線，(right,bottom)點至(left,bottom)
dc.LineTo(left,top);//畫左邊線，(left,bottom)點至(left,top)