Drawing Perpendicular Line of given point in Vb.net

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VB

Hi
I am developing an application in vb.net and want to draw perpendicular line against a parallel line
Like but not able to do if anyone know how to do please help
Thanks in Advance
like


http://tinypic.com/r/6h5nqt/5[^]

but not able to do if anyone know how to do please help
Thanks in Advance


I am using the code to for creating the line is..............

Public Class Form2
   
    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        picRegion.Image = Image.FromFile("C:/ss.jpg")

    End Sub
    Private m_BufferGraphics As Graphics
    Private m_Drawing As Boolean
    Private m_BufferBitmap As Bitmap
    Private m_X1 As Integer
    Private m_Y1 As Integer
    Private m_X2 As Integer
    Private m_Y2 As Integer
    Private m_X3 As Integer
    Private m_Y3 As Integer
    Private m_X4 As Integer
    Private m_Y4 As Integer
    Private Sub PictureBox1_MouseDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles picRegion.MouseDown
        If e.Button <> MouseButtons.Left Then Exit Sub
        m_Drawing = True
        SaveSnapshot()
        m_X1 = e.X
        m_Y1 = e.Y
    End Sub

    Private Sub SaveSnapshot()
        Dim new_bitmap As Bitmap
        new_bitmap = New Bitmap(Me.picRegion.Image.Size.Width, Me.picRegion.Image.Size.Height, Me.picRegion.CreateGraphics())
        m_BufferGraphics = Graphics.FromImage(picRegion.Image)
        m_BufferBitmap = new_bitmap
    End Sub

    Private Sub PrivewForm(ByVal gr As Graphics)
        If Not (m_BufferBitmap Is Nothing) Then gr.DrawImage(m_BufferBitmap, 0, 0)
    End Sub

    Private Sub PictureBox1_MouseMove(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles picRegion.MouseMove
        If Not m_Drawing Then Exit Sub
        m_X2 = e.X
        m_Y2 = e.Y
        PrivewForm(Me.picRegion.CreateGraphics())
        Me.picRegion.Refresh()
        Dim pen As New Pen(Color.Crimson, 3)
        Me.picRegion.CreateGraphics().DrawLine(pen, m_X1, m_Y1, m_X2, m_Y2)
        PrivewForm(Me.picRegion.CreateGraphics())

        'perpendicular line
      

    End Sub
  
    Private Sub PictureBox1_MouseUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles picRegion.MouseUp
        If Not m_Drawing Then Exit Sub
        m_Drawing = False
        m_X2 = e.X
        m_Y2 = e.Y
        Dim pen2 As New Pen(Color.Crimson, 3)
        m_BufferGraphics.DrawLine(pen2, m_X1, m_Y1, e.X, e.Y)
        Me.picRegion.Refresh()
        If m_Y1 = m_Y2 Then
            m_X3 = m_X1
            m_Y3 = m_Y1 - 15
            m_X4 = m_X1
            m_Y4 = m_Y1 + 15
            Dim pen31 As New Pen(Color.Cyan, 3)
            m_BufferGraphics.DrawLine(pen31, m_X3, m_Y3, m_X4, m_Y4)
            Me.picRegion.Refresh()

            m_X3 = m_X2
            m_Y3 = m_Y2 - 15
            m_X4 = m_X2
            m_Y4 = m_Y2 + 15
            Dim pen32 As New Pen(Color.Cyan, 3)
            m_BufferGraphics.DrawLine(pen32, m_X3, m_Y3, m_X4, m_Y4)
            Me.picRegion.Refresh()
        
        End If

    End Sub
End Class

in mouse up event where i have usage If m_Y1 = m_Y2 , this condition is only when a line is horizontal but if line is not horizontal perpendicular line is not generating.
sorry for bad English