Private Sub AnimationTimer_Timer()
Const R = 500
Static X As Single
Static Y As Single
Static Vx As Single
Static Vy As Single
Static done_before As Boolean

    If Not done_before Then
        done_before = True
        Randomize
        Vx = 50 + Rnd * 50
        Vy = 50 + Rnd * 50
        X = ScaleWidth / 2
        Y = ScaleHeight / 2
    End If
    
    ' Clear the backdrop.
    Backdrop.Line (0, 0)-(ScaleWidth, ScaleHeight), _
        Backdrop.BackColor, BF
    
    ' Draw the circle.
    Backdrop.Circle (X, Y), R
    Backdrop.Picture = Backdrop.Image
    MDIForm1.Picture = Backdrop.Picture
    
    ' Move the circle.
    X = X + Vx
    If (X + R > ScaleWidth) Or (X - R < 0) Then
        X = X - Vx
        Vx = -Vx
    End If
    Y = Y + Vy
    If (Y + R > ScaleHeight) Or (Y - R < 0) Then
        Y = Y - Vy
        Vy = -Vy
    End If
End Sub

Private Sub MDIForm_Resize()
    Backdrop.Move 0, 0, ScaleWidth, ScaleHeight
End Sub