private void button3_Click(object sender, EventArgs e)
{
_myBitmap = new Bitmap(pictureBox1.Width, pictureBox1.Height);
_g = Graphics.FromImage(_myBitmap);
WuLine wu = new WuLine();
Point2D p1 = new Point2D((double)numericUpDown1.Value, (double)numericUpDown2.Value);
Point2D p2 = new Point2D((double)numericUpDown3.Value, (double)numericUpDown4.Value);
wu.DrawLine(_g, p1, p2);
pictureBox1.Image = _myBitmap;
}