Public Class Form1
 
    Private Sub Form1_Click(ByVal sender As Object, ByVal e As _
      System.EventArgs) Handles Me.Click
        Invalidate()
    End Sub
 
    Private Sub Form1_MouseMove(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
 
        Dim g As Graphics = CreateGraphics()
        Dim p As Pen = New Pen(BackColor, 0)
 
        Dim ptMitte As New PointF(CSng(ClientSize.Width / 2), CSng( _
          ClientSize.Height / 2))
 
        Static ptmaus As New PointF
 
        ' Löschen
        g.DrawLine(p, ptMitte, ptmaus)
 
        ' Lote
        g.DrawLine(p, ptmaus, New PointF(ptMitte.X, ptmaus.Y))
        g.DrawLine(p, ptmaus, New PointF(ptmaus.X, ptMitte.Y))
 
        ' Sichtbar zeichnen
        ptmaus.X = CSng(e.X)
        ptmaus.Y = CSng(e.Y)
        p.Color = Color.Red
        g.DrawLine(p, ptMitte, ptmaus)
 
        ' Lote
        p.Color = Color.Green
        g.DrawLine(p, ptmaus, New PointF(ptMitte.X, ptmaus.Y)) ' Strich ist 
        ' oben, muss nach unten
        g.DrawLine(p, ptmaus, New PointF(ptmaus.X, ptMitte.Y))
 
    End Sub
 
End Class

Public Class Form1
    Private Sub Form1_MouseMove(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
        Static ptmaus As New Point
        Using g As Graphics = CreateGraphics(), p As New Pen(BackColor)
            Dim ptMitte As New Point(ClientSize.Width / 2, ClientSize.Height / _
              2)
            g.DrawLine(p, ptMitte, ptmaus)
            g.DrawLine(p, ptmaus.X, ptMitte.Y, ptMitte.X, ptMitte.Y)
            g.DrawLine(p, ptmaus, New Point(ptmaus.X, ptMitte.Y))
            ptmaus = e.Location
            g.DrawLine(Pens.Red, ptMitte, ptmaus)
            g.DrawLine(Pens.Green, e.X, ptMitte.Y, ptMitte.X, ptMitte.Y)
            g.DrawLine(Pens.Blue, ptmaus, New Point(ptmaus.X, ptMitte.Y))
        End Using
    End Sub
End Class