[.NET] How to draw on desktop

This is a demo for draw on desktop.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace DrawDesktop
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            IntPtr hdc = GetDCEx(GetDesktopWindow(), IntPtr.Zero, 1027);
            using (Graphics g = Graphics.FromHdc(hdc))
            {
                g.FillEllipse(Brushes.Red, 0, 0, 400, 400);
            }
        }

        [DllImport("user32.dll")]
        static extern IntPtr GetDesktopWindow();

        [DllImport("user32.dll")]
        static extern IntPtr GetDCEx(IntPtr hwnd, IntPtr hrgn, uint flags);
    }
}