visual basic 画图问题。作一个沿正弦曲线运动的小球的动画。代码如下

'用Form的BackColor把前一个圆覆盖掉
Dim k As Integer

Private Sub Form_Load()
Form1.ScaleWidth = 3600 '把屏幕坐标刻度改了下，画出来好看点
Form1.ScaleHeight = 2500
Form1.DrawWidth = 2
Timer1.Interval = 10
End Sub

Private Sub Form_Resize() '改变窗口尺寸，坐标不变
Form1.Cls '这里的Cls是改变大小时用的
Form1.ScaleWidth = 3600
Form1.ScaleHeight = 2500
End Sub

Private Sub Timer1_Timer()
Dim i As Integer
Form1.Line (0, Form1.ScaleHeight / 2)-(Form1.ScaleWidth, Form1.ScaleHeight / 2)
Form1.Line (Form1.ScaleWidth / 2, 0)-(Form1.ScaleWidth / 2, Form1.ScaleHeight)
For i = 0 To 3600
PSet (i, 1200 * Sin(3.14 * i / (180 * 10)) + Form1.ScaleHeight / 2)
Next
Form1.Circle (k, 1200 * Sin(3.14 * k / (180 * 10)) + Form1.ScaleHeight / 2), 40, Form1.BackColor '把前一点点画成背景色
If k < 3600 Then
k = k + 10
Else
k = 0
End If
Form1.Circle (k, 1200 * Sin(3.14 * k / (180 * 10)) + Form1.ScaleHeight / 2), 40, vbRed
End Sub

感情一句都没写啊