C# デスクトップに直接グラフィックス描画

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Runtime.InteropServices;

class Program {
    [DllImport("User32.dll")]
    static extern IntPtr GetDC(IntPtr hwnd);

    [DllImport("User32.dll")]
    static extern void ReleaseDC(IntPtr hwnd, IntPtr dc);

    static void Main(string[] args) {
        IntPtr desktopDC = GetDC(IntPtr.Zero);
        using (Graphics g = Graphics.FromHdc(desktopDC)) {
            g.FillEllipse(System.Drawing.Brushes.Red, 100, 100, 30, 30);
        }

        ReleaseDC((IntPtr.Zero, desktopDC);
    }
}