Public Class frmPolygon
 
    Dim hbmp As Drawing.Bitmap
    Dim vbmp As Drawing.Bitmap
    Dim grp As Drawing.Graphics
    Dim myPoints As New Collections.Generic.List(Of Point)
 
    Private Sub frmPolygon_Load(ByVal sender As System.Object, _
                ByVal e As System.EventArgs) Handles MyBase.Load
 
        hbmp = New Bitmap("Pfad und Name der Hintergrund-Zeichnung")
        pbox.BackgroundImage = hbmp
        pbox.BackgroundImageLayout = ImageLayout.None
        vbmp = New Bitmap(hbmp.Width, hbmp.Height)
        grp = Graphics.FromImage(vbmp)
        grp.Clear(Color.Transparent)
        pbox.Image = vbmp
    End Sub
 
    Private Sub pbox_MouseDown(ByVal sender As Object, _
        ByVal e As System.Windows.Forms.MouseEventArgs) Handles pbox.MouseDown
        myPoints.Add(New Point(e.X, e.Y))
        DrawFigure()
    End Sub
 
    Private Sub DrawFigure()
        grp.Clear(Color.Transparent)
        For i As Integer = 0 To myPoints.Count - 1
            grp.DrawEllipse(New Pen(Color.Red, 1), myPoints(i).X - 2, myPoints( _
              i).Y - 2, 4, 4)
            If i > 0 Then
                grp.DrawLine(New Pen(Color.Blue, 1), myPoints(i - 1), myPoints( _
                  i))
            End If
        Next i
        pbox.Invalidate() : pbox.Update()
    End Sub
 
    Private Sub pbox_MouseMove(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.MouseEventArgs) Handles pbox.MouseMove
        If myPoints.Count < 1 Then Exit Sub
        DrawFigure()
        Dim lp As Point = myPoints(myPoints.Count - 1)
        Dim mp As Point = New Point(e.X, e.Y)
        grp.DrawLine(New Pen(Color.Black, 1), lp, mp)
        pbox.Invalidate() : pbox.Update()
    End Sub
End Class