How to set Forms Background as transparent?

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;
//Needed
 
namespace Xcube.View
{
public partial class Login : Form
{

public Login()
{
InitializeComponent();
}

private void Login_Load(object sender, EventArgs e)
{
UpdateFormDisplay(this.BackgroundImage);

}
 

//protected override void OnPaint(PaintEventArgs e)
//{
// //Call our drawing function
// UpdateFormDisplay(this.BackgroundImage);
 
//}
protected override CreateParams CreateParams
{
get
{
CreateParams cp = base.CreateParams;
cp.ExStyle |= 0x00080000; // Required: set WS_EX_LAYERED extended style
return cp;
}
}
public void UpdateFormDisplay(Image backgroundImage)
{
IntPtr screenDc = API.GetDC(IntPtr.Zero);
IntPtr memDc = API.CreateCompatibleDC(screenDc);
IntPtr hBitmap = IntPtr.Zero;
IntPtr oldBitmap = IntPtr.Zero;
 
try
{
//Display-image
Bitmap bmp = new Bitmap(backgroundImage);
hBitmap = bmp.GetHbitmap(Color.FromArgb(0)); //Set the fact that background is transparent
oldBitmap = API.SelectObject(memDc, hBitmap);
 
//Display-rectangle
Size size = bmp.Size;
Point pointSource = new Point(0, 0);
Point topPos = new Point(this.Left, this.Top);
 
//Set up blending options
API.BLENDFUNCTION blend = new API.BLENDFUNCTION();
blend.BlendOp = API.AC_SRC_OVER;
blend.BlendFlags = 0;
blend.SourceConstantAlpha = 255;
blend.AlphaFormat = API.AC_SRC_ALPHA;
 
API.UpdateLayeredWindow(this.Handle, screenDc, ref topPos, ref size, memDc, ref pointSource, 0, ref blend, API.ULW_ALPHA);
 
//Clean-up
bmp.Dispose();
API.ReleaseDC(IntPtr.Zero, screenDc);
if (hBitmap != IntPtr.Zero)
{
API.SelectObject(memDc, oldBitmap);
API.DeleteObject(hBitmap);
}
API.DeleteDC(memDc);
}
catch (Exception)
{
}
}


 



}
internal class API
{
public const byte AC_SRC_OVER = 0x00;
public const byte AC_SRC_ALPHA = 0x01;
public const Int32 ULW_ALPHA = 0x00000002;
 
[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct BLENDFUNCTION
{
public byte BlendOp;
public byte BlendFlags;
public byte SourceConstantAlpha;
public byte AlphaFormat;
}
 
[DllImport("user32.dll", ExactSpelling = true, SetLastError = true)]
public static extern bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref Point pptDst, ref Size psize, IntPtr hdcSrc, ref Point pprSrc, Int32 crKey, ref BLENDFUNCTION pblend, Int32 dwFlags);
 

[DllImport("user32.dll", ExactSpelling = true, SetLastError = true)]
public static extern IntPtr GetDC(IntPtr hWnd);
 
[DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
public static extern IntPtr CreateCompatibleDC(IntPtr hDC);
 
[DllImport("user32.dll", ExactSpelling = true)]
public static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);
 
[DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
public static extern bool DeleteDC(IntPtr hdc);
 

[DllImport("gdi32.dll", ExactSpelling = true)]
public static extern IntPtr