Public Class UserControl2
    Inherits System.Windows.Forms.UserControl

#Region " Windows 窗体设计器生成的代码 "

    Public Sub New()
        MyBase.New()

        '该调用是 Windows 窗体设计器所必需的。
        InitializeComponent()

        '在 InitializeComponent() 调用之后添加任何初始化

    End Sub

    'UserControl 重写 dispose 以清理组件列表。
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Windows 窗体设计器所必需的
    Private components As System.ComponentModel.IContainer

    '注意: 以下过程是 Windows 窗体设计器所必需的
    '可以使用 Windows 窗体设计器修改此过程。
    '不要使用代码编辑器修改它。
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        '
        'UserControl1
        '
        Me.Name = "UserControl2"

    End Sub

#End Region

    Public Class Line
        Inherits System.Windows.Forms.UserControl
        Public TopLC As System.Drawing.Color = System.Drawing.Color.White ''上线颜色
        Public FootLC As System.Drawing.Color = System.Drawing.Color.Black ''下线颜色
        Public LineT As Type ''直线类型
        Public Enum Type
            Tf ''凸
            Ft ''凹
            Flat ''平面
        End Enum
#Region " Windows 窗体设计器生成的代码 "
        Public Sub New()
            MyBase.New()
            ''该调用是 Windows 窗体设计器所必需的。
            InitializeComponent()
            ''在 InitializeComponent() 调用之后添加任何初始化
        End Sub
        ''UserControl 重写 dispose 以清理组件列表。
        Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
            If disposing Then
                If Not (components Is Nothing) Then
                    components.Dispose()
                End If
            End If
            MyBase.Dispose(disposing)
        End Sub
        ''Windows 窗体设计器所必需的
        Private components As System.ComponentModel.IContainer
        ''注意: 以下过程是 Windows 窗体设计器所必需的
        ''可以使用 Windows 窗体设计器修改此过程。
        ''不要使用代码编辑器修改它。
        <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
            ''
            ''Arrow
            ''
            Me.Name = "Arrow"
            Me.Size = New System.Drawing.Size(304, 72)
        End Sub
#End Region
#Region " 属性 "
        <System.ComponentModel.Description("直线类型：" & vbCrLf & "Tf ''凸" & vbCrLf & "Ft ''凹" & vbCrLf & "Flat ''平面")> Public Property LineType() As Type
            Get
                LineType = LineT
            End Get
            Set(ByVal Value As Type)
                LineT = Value
            End Set
        End Property
        <System.ComponentModel.Description("上线颜色")> Public Property TopLineColor() As System.Drawing.Color
            Get
                TopLineColor = TopLC
            End Get
            Set(ByVal Value As System.Drawing.Color)
                TopLC = Value
            End Set
        End Property
        <System.ComponentModel.Description("下线颜色")> Public Property FootLineColor() As System.Drawing.Color
            Get
                FootLineColor = FootLC
            End Get
            Set(ByVal Value As System.Drawing.Color)
                FootLC = Value
            End Set
        End Property
#End Region
        Private Sub Line_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
            Dim TopLine As New Pen(Me.TopLineColor)
            Dim FootLine As New Pen(Me.FootLineColor)
            Dim startX As Integer
            Dim startY As Integer
            Select Case LineT
                Case LineT.Flat
                    e.Graphics.DrawLine(TopLine, 0 + startX, 0, Me.Width + startX, 0)
                    e.Graphics.DrawLine(TopLine, 1 + startX, 1, Me.Width + startX, 1)
                Case LineT.Tf
                    e.Graphics.DrawLine(TopLine, 0 + startX, 0, Me.Width + startX, 0)
                    e.Graphics.DrawLine(FootLine, 1 + startX, 1, Me.Width + startX, 1)
                Case LineT.Ft
                    e.Graphics.DrawLine(FootLine, 0 + startX, 0, Me.Width + startX, 0)
                    e.Graphics.DrawLine(TopLine, 1 + startX, 1, Me.Width + startX, 1)
            End Select
        End Sub
        Private Sub Line_Resize(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Resize
            Me.Height = 2
        End Sub
    End Class


End Class
[color=FF0000]上线颜色[/color]

以上是自定义的直线控件.
我的问题是：什么是上线颜色？
        什么是下线颜色？
        直线的类型“凸”“凹”“平”又是什么含义？