Public Class Form1
 
 
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles _
      Button1.Click
        Dim x As String
        Dim y As String
        Dim x1 As String
        Dim y1 As String
 
 
        Dim myBrush As New System.Drawing.SolidBrush( _
          System.Drawing.Color.LemonChiffon)
        Dim formGraphics As System.Drawing.Graphics
        formGraphics = Me.GroupBox1.CreateGraphics()
        x = TextBox1.Text
        y = TextBox2.Text
        x1 = (600 - x) / 2
        y1 = (400 - y) / 2
 
        'wenn leer
        If TextBox1.Text = "" Or
            TextBox2.Text = "" Then
 
        Else
            Label1.Text = x / y
            formGraphics.FillRectangle(myBrush, New Rectangle(x1, y1, x, y))
        End If
 
 
    End Sub
 
 
End Class

Private Sub Rescale(x As Double, y As Double, _
                       xmax As Double, ymax As Double, _
                 ByRef xr As Double, ByRef yr As Double)
 
    If x < 1 Or y < 1 or xmax < 10 or ymax < 10 Then
       Throw New ArgumentException
    End If
 
    xr = x : yr = y
 
    If xr > xmax Then
       xr = xmax : yr = y * xmax / x
    End If
 
    If yr > ymax Then
       yr = ymax : xr = x * ymax / y
    End If
 
End Sub

Private Sub Rescale(x As Integer, y As Integer, _
                    xmax As Integer, ymax As Integer, _
              ByRef xr As Integer, ByRef yr As Integer)
 
    If x < 1 Or y < 1 Or ymax < 10 Or xmax < 10 Then
       Throw New ArgumentException
    End If
 
    xr = x : yr = y
 
    If xr > xmax Then
       xr = xmax : yr = CInt(Math.Floor(y * xmax / x))
    End If
 
    If yr > ymax Then
       yr = ymax : xr = CInt(Math.Floor(x * ymax / y))
    End If
 
End Sub

Private Sub groupbox1_Paint(sender As Object, 
              e As System.Windows.Forms.PaintEventArgs) _
              Handles groupbox1.Paint
 
     Const xmax As Integer = 580
     Const ymax As Integer = 380
 
     Dim x, y, xr, yr, x1, y1 As Integer
 
     If Not Integer.TryParse(textbox1.Text, x) Then Exit Sub
     If Not Integer.TryParse(textbox2.Text, y) Then Exit Sub
 
     Rescale(x, y, xmax, ymax, xr, yr) 'Integer-Variante von oben
 
     x1 = CInt((600 - xr) / 2)
     y1 = CInt((400 - yr) / 2)
 
     Using myBrush As New SolidBrush(Color.LemonChiffon)
        e.Graphics.FillRectangle(myBrush, New Rectangle(x1, y1, xr, yr))
     End Using
End Sub

Private Sub Button1_Click(sender As Object, _
        e As System.EventArgs) Handles Button1.Click
 
   groupbox1.Invalidate()
 
End Sub

Public Class Form1
 
    Private Sub Groupbox1_Paint(sender As Object, e As _
      System.Windows.Forms.PaintEventArgs) Handles GroupBox1.Paint
 
        e.Graphics.DrawLine(Pens.Brown, 100, 690, 100, 100)
        e.Graphics.DrawLine(Pens.Brown, 100, 690, 900, 690)
        e.Graphics.DrawLine(Pens.Brown, 100, 100, 471, 100)
        e.Graphics.DrawLine(Pens.Brown, 471, 100, 471, 149)
        e.Graphics.DrawLine(Pens.Brown, 471, 149, 561, 149)
        e.Graphics.DrawLine(Pens.Brown, 561, 149, 561, 100)
        e.Graphics.DrawLine(Pens.Brown, 561, 100, 832, 100)
        e.Graphics.DrawLine(Pens.Brown, 832, 100, 832, 149)
        e.Graphics.DrawLine(Pens.Brown, 832, 149, 900, 149)
        e.Graphics.DrawLine(Pens.Brown, 900, 149, 900, 690)
 
    End Sub
 
 
End Class

    Private Function DrawFigure()
 
        'Ausgangsgröße
        Dim x() As Integer = {100, 471, 561, 832, 900}
        Dim y() As Integer = {100, 149, 690}
 
        'Größe der Kerben (Auslinkungen?)
        Dim kerbtiefe As Integer = 40, kerblänge1 As Integer = 90, kerblänge2 = _
          70
 
 
        'skalierbare Punkte der Figur
        Dim pts() As Point = {New Point(x(0), y(0)), New Point(x(0), y(2)),
                              New Point(x(4), y(2)), New Point(x(1), y(0)),
                              New Point(x(2), y(0))}
 
        'Zentrum der Skalierung festlegen
        Dim center As Point = pts(0)
 
        'Skalierungsfaktoren (z.B. halbe Ausgangs-Größe)
        Dim ScaleX As Single = 0.5
        Dim ScaleY As Single = 0.5
 
        'Skalierbare Punkte skalieren (Rescale Methode)
        For i As Integer = 0 To pts.Length - 1
            pts(i) = Rescale(pts(i), center, ScaleX, ScaleY)
        Next
 
        'Zeichnung (pb sei eine Picurebox auf der Form)
        pb.Image = New Bitmap(1000, 1000)
 
        Using g As Graphics = Graphics.FromImage(pb.Image),
            p As New Pen(Color.Brown, 2)
 
            'Skalierte Punkte zeichnen
            g.DrawLine(p, pts(1), pts(0))
            g.DrawLine(p, pts(1), pts(2))
            g.DrawLine(p, pts(0), pts(4))
 
            'Einkerbung  relativ zu pts(4)
            g.DrawLine(p, pts(4), New Point(pts(4).X, pts(4).Y + kerbtiefe))
 
            g.DrawLine(p, New Point(pts(4).X, pts(4).Y + kerbtiefe), 
                 New Point(pts(4).X + kerblänge1, pts(4).Y + kerbtiefe))
 
            g.DrawLine(p, New Point(pts(4).X + kerblänge1, pts(4).Y + _
              kerbtiefe), 
                          New Point(pts(4).X + kerblänge1, pts(4).Y))
 
            'Verbindungslinie zwischen Kerben
            g.DrawLine(p, New Point(pts(4).X + kerblänge1, pts(4).Y), 
                          New Point(pts(2).X - kerblänge2, pts(4).Y))
 
            'zweite Einkerbung (relativ zu Punkt 2 und Punkt 4)
            g.DrawLine(p, New Point(pts(2).X - kerblänge2, pts(4).Y), 
                          New Point(pts(2).X - kerblänge2, pts(4).Y + _
                            kerbtiefe))
            g.DrawLine(p, New Point(pts(2).X - kerblänge2, pts(4).Y + _
            kerbtiefe), 
                          New Point(pts(2).X, pts(4).Y + kerbtiefe))
 
            'rechter Rand des Rechtecks ab Kerbung
            g.DrawLine(p, New Point(pts(2).X, pts(4).Y + kerbtiefe), pts(2))
 
        End Using
 
    End Function
 
 
 
    Private Function Rescale(p As Point, center As Point, 
             scalefactorX As Single, scalefactorY As Single) As Point
 
        Return New Point(CInt((p.X - center.X) * scalefactorX + center.X), 
                         (p.Y - center.Y) * scalefactorY + center.Y)
    End Function