Messengerのような画面制御について

Public Class Form1

    Private Const WM_NCHITTEST As Integer = &H84
    Private Const HTERROR = (-2)
    Private Const HTTRANSPARENT = (-1)
    Private Const HTNOWHERE = 0
    Private Const HTCLIENT = 1
    Private Const HTCAPTION = 2
    Private Const HTSYSMENU = 3
    Private Const HTGROWBOX = 4
    Private Const HTSIZE = HTGROWBOX
    Private Const HTMENU = 5
    Private Const HTHSCROLL = 6
    Private Const HTVSCROLL = 7
    Private Const HTMINBUTTON = 8
    Private Const HTMAXBUTTON = 9
    Private Const HTLEFT = 10
    Private Const HTRIGHT = 11
    Private Const HTTOP = 12
    Private Const HTTOPLEFT = 13
    Private Const HTTOPRIGHT = 14
    Private Const HTBOTTOM = 15
    Private Const HTBOTTOMLEFT = 16
    Private Const HTBOTTOMRIGHT = 17
    Private Const HTBORDER = 18
    Private Const HTREDUCE = HTMINBUTTON
    Private Const HTZOOM = HTMAXBUTTON
    Private Const HTSIZEFIRST = HTLEFT
    Private Const HTSIZELAST = HTBOTTOMRIGHT

    Public Property ClientRectangleOnly() As Boolean
        Get
            Return Me.Region IsNot Nothing
        End Get
        Set(ByVal value As Boolean)
            If value = Me.ClientRectangleOnly Then Exit Property
            If Me.Region Is Nothing Then
                Dim r As Rectangle
                r.X = Me.PointToScreen(Me.ClientRectangle.Location).X - Me.Left
                r.Y = Me.PointToScreen(Me.ClientRectangle.Location).Y - Me.Top
                r.Width = Me.ClientRectangle.Width
                r.Height = Me.ClientRectangle.Height
                Me.Region = New Region(r)
            Else
                Me.Region = Nothing
            End If
        End Set
    End Property

    Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
        Select Case m.Msg
            Case WM_NCHITTEST
                Dim p As Point
                p = Me.PointToClient(New Point(m.LParam.ToInt32 Mod 65536, m.LParam.ToInt32 \\ 65536))

                If p.X > Me.ClientRectangle.Right Then Exit Select
                If p.X < Me.ClientRectangle.Left Then Exit Select
                If p.Y < Me.ClientRectangle.Top Then Exit Select
                If p.Y > Me.ClientRectangle.Bottom Then Exit Select

                If p.X < Me.ClientRectangle.Left + 5 Then
                    If p.Y < Me.ClientRectangle.Top + 5 Then
                        m.Result = HTTOPLEFT
                        Exit Sub
                    End If
                    If p.Y > Me.ClientRectangle.Bottom - 5 Then
                        m.Result = HTBOTTOMLEFT
                        Exit Sub
                    End If
                    m.Result = HTLEFT
                    Exit Sub
                End If
                If p.X > Me.ClientRectangle.Right - 5 Then
                    If p.Y < Me.ClientRectangle.Top + 5 Then
                        m.Result = HTTOPRIGHT
                        Exit Sub
                    End If
                    If p.Y > Me.ClientRectangle.Bottom - 5 Then
                        m.Result = HTBOTTOMRIGHT
                        Exit Sub
                    End If
                    m.Result = HTRIGHT
                    Exit Sub
                End If
                If p.Y < Me.ClientRectangle.Top + 5 Then
                    m.Result = HTTOP
                    Exit Sub
                End If
                If p.Y > Me.ClientRectangle.Bottom - 5 Then
                    m.Result = HTBOTTOM
                    Exit Sub
                End If

                m.Result = HTCAPTION
                Exit Sub
        End Select
        MyBase.WndProc(m)
    End Sub

    Private Sub Form1_ClientSizeChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.ClientSizeChanged
        If Me.ClientRectangleOnly Then
            Dim r As Rectangle
            r.X = Me.PointToScreen(Me.ClientRectangle.Location).X - Me.Left
            r.Y = Me.PointToScreen(Me.ClientRectangle.Location).Y - Me.Top
            r.Width = Me.ClientRectangle.Width
            r.Height = Me.ClientRectangle.Height
            Me.Region = New Region(r)
        End If
    End Sub

    Private Sub Form1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown
        If e.Alt Then
            If Me.ClientRectangleOnly Then
                Me.ClientRectangleOnly = False
            Else
                Me.ClientRectangleOnly = True
            End If
            e.Handled = True
        End If
    End Sub

End Class