C# フォームを突き抜けてフォームの後ろ側をクリックできるようにしたい

Option Strict On
Imports System.Runtime.InteropServices
Imports System.Drawing.Imaging

Public Class Form1

    <DllImport("user32.dll")> _
    Private Shared Function GetDC( _
        ByVal hWnd As IntPtr) _
        As IntPtr
    End Function

    <DllImport("user32.dll")> _
    Private Shared Function ReleaseDC( _
        ByVal hWnd As IntPtr, _
        ByVal hDC As IntPtr) _
        As Integer
    End Function

    <DllImport("user32.dll")> _
    Private Shared Function UpdateWindow( _
        ByVal hWnd As IntPtr) _
        As Boolean
    End Function

    <DllImport("user32.dll")> _
    Private Shared Function RedrawWindow( _
        ByVal hWnd As IntPtr, _
        ByVal lprcUpdate As IntPtr, _
        ByVal hrgnUpdate As IntPtr, _
        ByVal flags As RDW) _
        As Boolean
    End Function

    'RedrawWindow() flags
    Private Enum RDW As Integer
        INVALIDATE = &H1
        INTERNALPAINT = &H2
        [ERASE] = &H4
        VALIDATE = &H8
        NOINTERNALPAINT = &H10
        NOERASE = &H20
        NOCHILDREN = &H40
        ALLCHILDREN = &H80
        UPDATENOW = &H100
        ERASENOW = &H200
        FRAME = &H400
        NOFRAME = &H800
    End Enum

    Private Sub RefreshDesktop()
        RedrawWindow(IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, RDW.ALLCHILDREN Or RDW.UPDATENOW Or RDW.ERASE Or RDW.INVALIDATE Or RDW.INTERNALPAINT)
        UpdateWindow(IntPtr.Zero)
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
        Dim hDC As IntPtr = GetDC(IntPtr.Zero)
        Using g As Graphics = Graphics.FromHdc(hDC)
            Dim f As New Form
            Dim b As New Bitmap(f.Width, f.Height)
            f.DrawToBitmap(b, New Rectangle(0, 0, b.Width, b.Height))
            Dim a As New ImageAttributes
            Dim m As New ColorMatrix
            m.Matrix00 = 1
            m.Matrix11 = 1
            m.Matrix22 = 1
            m.Matrix33 = 0.5
            m.Matrix44 = 1
            a.SetColorMatrix(m)
            Dim s As Rectangle = Screen.AllScreens(0).Bounds
            g.DrawImage(b, New Rectangle(New Point(CInt((s.Width - b.Width) / 2), CInt((s.Height - b.Height) / 2)), b.Size), 0, 0, b.Width, b.Height, GraphicsUnit.Pixel, a)
        End Using
        ReleaseDC(IntPtr.Zero, hDC)
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
        RefreshDesktop()
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim b1 As New Button
        b1.Text = "表示"
        Me.Controls.Add(b1)
        AddHandler b1.Click, AddressOf Button1_Click
        Dim b2 As New Button
        b2.Text = "消去"
        b2.Location = New Point(0, 30)
        Me.Controls.Add(b2)
        AddHandler b2.Click, AddressOf Button2_Click
    End Sub

End Class

using System;
using System.Drawing;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Drawing.Imaging;

public class Form1 : System.Windows.Forms.Form
{
	[DllImport("user32.dll")] private static extern IntPtr GetDC(IntPtr hwnd);
	[DllImport("user32.dll")] private  static extern IntPtr ReleaseDC(IntPtr hwnd, IntPtr hdc);
	[DllImport("user32.dll")] private static extern bool UpdateWindow(IntPtr hWnd);
	[DllImport("user32.dll")] public static extern bool RedrawWindow(IntPtr hWnd, IntPtr lprcUpdate, IntPtr hrgnUpdate, uint flags);

	//RedrawWindow() flags
	private enum RDW : int 
	{ 
		INVALIDATE = 0x1,
		INTERNALPAINT = 0x2,
		ERASE = 0x4,
		VALIDATE = 0x8,
		NOINTERNALPAINT = 0x10,
		NOERASE = 0x20,
		NOCHILDREN = 0x40,
		ALLCHILDREN = 0x80,
		UPDATENOW = 0x100,
		ERASENOW = 0x200,
		FRAME = 0x400,
		NOFRAME = 0x800
	}

	private void RefreshDesktop() 
	{ 
		RedrawWindow(IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, 
			(uint)(RDW.ALLCHILDREN | RDW.UPDATENOW | RDW.ERASE | RDW.INVALIDATE | RDW.INTERNALPAINT)); 
		UpdateWindow(IntPtr.Zero); 
	}

	private void button1_Click(object sender, System.EventArgs e)
	{
		IntPtr hDC = GetDC(IntPtr.Zero);
		using (Graphics g = Graphics.FromHdc(hDC))
		{
			Form f = new Form(); 
			//Bitmap b = new Bitmap(f.Width, f.Height); 
			//f.DrawToBitmap(b, new Rectangle(0, 0, b.Width, b.Height)); 
			//DrawToBitmapはFramework2.0対応のようなので、代わりに画像の表示で試す
			Bitmap b = new Bitmap(@"c:\\pic.jpg"); 
			ImageAttributes a = new ImageAttributes(); 
			ColorMatrix m = new ColorMatrix(); 
			m.Matrix00 = 1; 
			m.Matrix11 = 1; 
			m.Matrix22 = 1; 
			m.Matrix33 = 0.5f; 
			m.Matrix44 = 1; 
			a.SetColorMatrix(m); 
			Rectangle s = Screen.PrimaryScreen.Bounds;
			g.DrawImage(
				b,
				new Rectangle(new Point(System.Convert.ToInt32((s.Width - b.Width) / 2),
				System.Convert.ToInt32((s.Height - b.Height) / 2)), b.Size),
				0,
				0,
				b.Width,
				b.Height, GraphicsUnit.Pixel, a);
		}
		ReleaseDC(IntPtr.Zero, hDC);
	}

	private void button2_Click(object sender, System.EventArgs e)
	{
		RefreshDesktop();
	}

	private void Form1_Load(object sender, System.EventArgs e) 
	{ 
		Button b1 = new Button(); 
		b1.Text = "表示"; 
		this.Controls.Add(b1); 
		b1.Click += new EventHandler(button1_Click); 
		Button b2 = new Button(); 
		b2.Text = "消去"; 
		b2.Location = new Point(0, 30); 
		this.Controls.Add(b2); 
		b2.Click += new EventHandler(button2_Click); 
	}

	public Form1()
	{
		Load += new EventHandler(Form1_Load);
	}

	[STAThread]
	static void Main() 
	{
		Application.Run(new Form1());
	}
}