draw string in center of a rectangle

My form has a picturebox that draw a shape with mouse down and up.
Attachment 186399
my problem is the location of text"020"! I want to draw it in center of rectangle.
please guide me. my codes are:

Code:

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Imports System.Drawing.Drawing2D

Public Class Form4

    Private NewSegment As Segment
    Private Segments As New List(Of Segment)
    Private Sub PictureBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseDown

        NewSegment = New Segment(e.Location, e.Location)
        Segments.Add(NewSegment)
        PictureBox1.Invalidate()
    End Sub

    Private Sub PictureBox1_MouseMove(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseMove
        If NewSegment Is Nothing Then Return
        NewSegment.Point2 = e.Location
        PictureBox1.Invalidate()
    End Sub

    Private Sub PictureBox1_MouseUp(sender As Object, e As MouseEventArgs) Handles PictureBox1.MouseUp
        NewSegment = Nothing
        PictureBox1.Invalidate()
    End Sub

    Private Sub PictureBox1_Paint(sender As Object, e As PaintEventArgs) Handles PictureBox1.Paint
        e.Graphics.SmoothingMode = Drawing2D.SmoothingMode.AntiAlias
        For Each segment As Segment In Segments
            segment.Draw(e.Graphics, Nothing)
        Next
    End Sub
End Class

Class Segment
    Private Const RADIUS As Integer = 15
    Private Shared rc_r As New Rectangle(New Point(-RADIUS, -RADIUS), New Size(RADIUS * 1.5, RADIUS * 1.5)) 'for rectangle
    Private pt1, pt2 As Point
    Private angle As Double = 0
    Private length As Double = 0
    Private Shared pen1 As New Pen(Color.Black, 1.5)
    Private Shared drawFontF As New Font("times new roman", 8, style:=FontStyle.Bold)
    Private Shared SF As StringFormat
    Public Sub New(startPoint As Point, endPoint As Point)
        Point1 = startPoint
        Point2 = endPoint
    End Sub

    Public Property Point1 As Point
        Get
            Return pt1
        End Get
        Set(value As Point)
            pt1 = value
            UpdateAngleAndLength()
        End Set
    End Property

    Public Property Point2 As Point
        Get
            Return pt2
        End Get
        Set(value As Point)
            pt2 = value
            UpdateAngleAndLength()
        End Set
    End Property

    Private Sub UpdateAngleAndLength()
        angle = Math.Atan2(Point2.Y - Point1.Y, Point2.X - Point1.X) * 180.0 / Math.PI
        length = Math.Sqrt(Math.Pow(Point2.X - Point1.X, 2) + Math.Pow(Point2.Y - Point1.Y, 2))
    End Sub
    Public Sub Draw(gr As System.Drawing.Graphics, R As Rectangle)

        If Point1 = Point2 Then Return
        ' save the current state of the graphics
        Dim curState As GraphicsState = gr.Save()

        ' move the origin to the start point of the line
        gr.TranslateTransform(Point1.X, Point1.Y)
        ' rotate the whole surface
        gr.RotateTransform(angle)

        ' draw the line on the x-axis
        gr.DrawLine(pen1, 0, 0, CInt(length), 0)

        ' move the origin along the x-axis to where the center of the circle should be
        gr.TranslateTransform(length + RADIUS, 0)
        gr.DrawRectangle(pen1, rc_r) ' for rectangle

        ' orient back to the "normal" so the 90 is upright
        gr.RotateTransform(-angle)
        ' draw the 90
        Dim rcS As New Rectangle(New Point(-RADIUS, -RADIUS), New Size(RADIUS * 1.5, RADIUS * 1.5))

        gr.DrawString("020", drawFontF, Brushes.DimGray, rcS, SF)

        gr.Restore(curState)
    End Sub
End Class

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how change 'RCS' ?

Read the documentation for that DrawString method, including the other overloads, and you'll find the answer. ALWAYS read the documentation. You can go directly to it by clicking the member name in code and pressing F1.