用image画了个函数图，怎样能使这个函数图从左到右慢慢出现？(15分)

就比如我画了个正弦图，我想在画布上按一定时间规律慢慢画出来，我们可以清楚地看到画的过程，不是直接出现结果？？

用定时器画：放个定时器，Interval:=100;Enabled:=False;
procedure TForm1.Timer1Timer(Sender: TObject);
var Y:Integer;
begin
Y:=Trunc(Sin(X/90*3.14)*100);
Image1.Picture.Bitmap.Canvas.LineTo(10+X,150-Y);
Inc(X);
Timer1.Enabled:=X<400;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
Image1.Picture.Bitmap.Height:=Image1.Height;
Image1.Picture.Bitmap.Width:=Image1.Width;
Image1.Picture.Bitmap.Canvas.MoveTo(10,150);
X:=0;
Timer1.Enabled:=True;
end;

谢谢