Public Class Form1
    Dim plist As New List(Of Point)
    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) _
      Handles MyBase.Load
        Me.DoubleBuffered = True
    End Sub
 
    Private Sub Form1_MouseDown(sender As Object, e As _
      System.Windows.Forms.MouseEventArgs) Handles Me.MouseDown
        plist.Add(New Point(e.X, e.Y))
        Me.Invalidate()
    End Sub
 
    Private Sub Form1_Paint(sender As Object, e As _
      System.Windows.Forms.PaintEventArgs) Handles Me.Paint
        Dim g As Graphics = e.Graphics
        For Each p As Point In plist
            g.DrawLine(Pens.Black, p.X, p.Y - 5, p.X, p.Y + 5)
            g.DrawLine(Pens.Black, p.X - 5, p.Y, p.X + 5, p.Y)
        Next
    End Sub
End Class