在delphi中的canvas属性中画图为什么画多了就不显示了呢？

Question

                    form1.image3.Canvas.Pen.Color:=clblack;
                      form1.image3.Canvas.Pen.Width:=3;
                      form1.Image3.Canvas.Brush.Color:=clwhite;
                      form1.image3.Canvas.Rectangle((34+60*3),22,(85+60*3),94);
                      form1.image3.Canvas.Rectangle((48+60*3),8,(70+60*3),22);
                     c2:=round((buffer1[28]*18)/1000);
                     form1.Image3.Canvas.Pen.Width:=1;
                     form1.Image3.Canvas.Pen.Color:=clwhite;
                     form1.Image3.Canvas.Brush.Color:=clgreen;
                     form1.Image3.Canvas.Rectangle((34+60*3),(94-c2),(85+60*3),94);
                  大侠们指教呀

Answer 1

画前对Canvas进行Lock，画完后UnLock