vb.net Bitmap Drawing

Public Class Form1
  Dim BMP As New Drawing.Bitmap(640, 480)
  Dim GFX As Graphics = Graphics.FromImage(BMP)
  Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    FX.FillRectangle(Brushes.White, 0, 0, PictureBox1.Width, PictureBox1.Height)
    GFX.DrawLine(Pens.Red, 10, 10, 50, 50)
    GFX.DrawString("Robomatics", SystemFonts.DefaultFont, Brushes.Black, 60, 60)
    PictureBox1.Image = BMP
  End Sub
  Private Sub PictureBox1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PictureBox1.Click
    BMP.SetPixel(MousePosition.X - Me.Location.X - PictureBox1.Location.X - 4, MousePosition.Y - Me.Location.Y - PictureBox1.Location.Y - 30, Color.Black)
    GFX.DrawString("Robomatics", SystemFonts.DefaultFont, Brushes.Black, MousePosition.X - Me.Location.X - PictureBox1.Location.X - 4, MousePosition.Y -  Me.Location.Y - PictureBox1.Location.Y - 30)
    PictureBox1.Image = BMP
  End Sub
End Class