Dim stepy As Integer    '纵向移动增量
Dim stepx As Integer    '横向移动增量
Const LEFT_BUTTON = 1
Private Sub Form_MouseDown(Button As Integer, Shift As Integer, x As Single, y As Single)
    Dim x0 As Integer, y0 As Integer, a As Single, radius As Integer
    radius = Shape1.Width / 2              '圆的半径
    If Button = LEFT_BUTTON Then
        x0 = Shape1.Left + radius          '圆心的x坐标
        y0 = Shape1.Top + radius            '圆心的y坐标
        If x = x0 Then
            stepy = Sgn(y - y0) * 50
'            stepx = ?
        Else
            a = (y - y0) / (x - x0)          '斜率
            stepx = Sgn(x - x0) * 50
'            ? = a * stepx
            If Abs(stepy) > Abs(stepx) Then
                stepy = Sgn(y - y0) * 50
                stepx = stepy / a
            End If
        End If
'        ? = True
    Else
'        ? = False
    End If
End Sub
Private Sub Timer1_Timer()
'    Shape1.Move Shape1.Left + stepx, Shape1.Top + ?
End Sub