Graphics对象用于进行绘制；

从哪个对象获取的Graphics，然后进行绘制，就绘制到该对象上；

从位图获取Graphics，然后进行绘制，绘制到该位图上；

从某个控件获取Graphics，然后绘制，绘制到该控件上；

在form上添加5个控件，

        private void button2_Click(object sender, EventArgs e)
        {
            Rectangle rect1 = new Rectangle(20, 20, 30, 30);

            Graphics g1 = Graphics.FromHwnd(button1.Handle);
            g1.FillRectangle(Brushes.Green, rect1);

            Graphics g2 = Graphics.FromHwnd(textBox1.Handle);
            g2.FillRectangle(Brushes.Red, rect1);

            Graphics g3 = Graphics.FromHwnd(pictureBox1.Handle);
            g3.FillRectangle(Brushes.Blue, rect1);

            Rectangle rect2 = new Rectangle(10, 10, 30, 30);
            Graphics g4 = Graphics.FromHwnd(comboBox1.Handle);
            g4.FillRectangle(Brushes.Black, rect2);

            Graphics g5 = Graphics.FromHwnd(label1.Handle);
            g5.FillRectangle(Brushes.Black, rect2);

        }

从这5个控件获取Graphics，然后分别绘制一个小矩形；

从控件获取Graphics使用FromHwnd方法，参数是该控件的句柄；

    Graphics.FromHwnd(button1.Handle);