Option Strict Off
 
Public Class Form1
 
    Dim sStr As String = "Bitte Maus hin und her bewegen. Warum bewegen sich" & _
      "beim selektierten Text einige Buchstaben."
    Dim oFont As Font = New Font("Courier New", 13)
    Dim strFormat As New StringFormat(StringFormat.GenericTypographic) With _
      {.FormatFlags = StringFormatFlags.MeasureTrailingSpaces}
    Dim iPos As Integer
 
    Private Sub Form1_Load(sender As Object, e As System.EventArgs) Handles _
      Me.Load
        Me.Size = New Size(1200, 120)
        Me.Left = 100
        PictureBox1.Location = New Point(0, 0)
        PictureBox1.Size = New Size(Me.ClientRectangle.Width, _
          Me.ClientRectangle.Height)
    End Sub
 
    Private Sub PictureBox1_MouseMove(sender As Object, e As _
      System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseMove
        iPos = e.X \ CInt(Me.CreateGraphics.MeasureString("X", oFont, _
        Integer.MaxValue, strFormat).Width)
        If iPos > sStr.Length Then iPos = sStr.Length
        PictureBox1.Invalidate()
    End Sub
 
    Private Sub PictureBox1_Paint(sender As Object, e As _
      System.Windows.Forms.PaintEventArgs) Handles PictureBox1.Paint
        Dim gra As Graphics = e.Graphics
        Dim iCharW As Single = Me.CreateGraphics.MeasureString("X", oFont, _
          Integer.MaxValue, strFormat).Width
        Dim iMitte As Integer = sStr.Length \ 2
        Dim iCenter As Single = iCharW * iMitte
        Dim iLeft As Integer
        Dim iRight As Integer
 
        'Zeile ausgeben
        gra.DrawString(sStr, oFont, Brushes.Black, 0, 20, strFormat)
 
        If iPos < iMitte Then
            iLeft = iPos
            iRight = iMitte
        ElseIf iPos > iMitte Then
            iLeft = iMitte
            iRight = iPos
        Else
            Exit Sub
        End If
 
        'Text markieren
        Dim iX As Single = iLeft * iCharW
        Dim iWidth As Single = (iRight - iLeft) * iCharW
 
        gra.FillRectangle(Brushes.Blue, iX, 20, iWidth, 25)
        gra.DrawString(sStr.Substring(iLeft, iRight - iLeft), oFont, _
          Brushes.White, iX, 20, strFormat)
    End Sub
End Class

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Jeder Mensch ist anders. Darum nimm jeden Menschen so wie er ist.