private void Form1_Resize(object sender, EventArgs e)
        {
            int new_form_height = 0;
            int new_form_width = 0;

            if(this.WindowState == FormWindowState.Maximized)
            {
                new_form_height = this.Height - old_form_height;
                new_form_width = this.Width - old_form_width;

                pictureBox1.Width += new_form_width;
                pictureBox1.Height += new_form_height;

                int x = panel1.Location.X;
                int y = panel1.Location.Y;
                panel1.SetBounds(x + new_form_width / 2, y + new_form_height, panel1.Width, panel1.Height);
                old_form_width = new_form_width;
                old_form_height = new_form_height;
            }
            else
            {
                pictureBox1.Width -= old_form_width;
                pictureBox1.Height -= old_form_height;

                int x = panel1.Location.X;
                int y = panel1.Location.Y;
                panel1.SetBounds(x - old_form_width / 2, y - old_form_height, panel1.Width, panel1.Height);
                old_form_width = this.Width;
                old_form_height = this.Height;
            }
        }