Need some help understanding this advanced code which uses threading, pointers, etc..

[akhileshbc]

Hi guys..

I had recently(2 months before ) found some code for locking the screen. Here's the link to that code submission in our CodeBank : http://www.vbforums.com/showthread.php?t=639579

I wish to get a clear idea of what it actually does. As it is a bit advanced code for me, I need your help.

Here's the main part of the code:

Public Function LockSystemAndShow(ByVal myDForm As Form) As Boolean
        myForm = myDForm
 
        'Dim owner As Control = TryCast(Form1.Button1, Control)
        Dim scr As Screen
        'If owner Is Nothing Then
        scr = Screen.PrimaryScreen
        'Else
        'scr = Screen.FromControl(owner)
        'End If
        Dim background As Bitmap = New Bitmap(scr.Bounds.Width, scr.Bounds.Height)
        Using g As Graphics = Graphics.FromImage(background)
 
            g.CopyFromScreen(0, 0, 0, 0, scr.Bounds.Size)
            Using br As Brush = New SolidBrush(Color.FromArgb(192, Color.Black))
                g.FillRectangle(br, scr.Bounds)
            End Using
 
            'If owner IsNot Nothing Then
            ' Dim form As Form = owner.FindForm()
            ' g.CopyFromScreen(form.Location, form.Location, form.Size)
            ' Using br As Brush = New SolidBrush(Color.FromArgb(128, Color.Black))
            ' g.FillRectangle(br, New Rectangle(Form.Location, Form.Size))
            'End Using
            'End If
 
        End Using
 
        Dim originalThread As IntPtr
        Dim originalInput As IntPtr
        Dim newDesktop As IntPtr
 
        originalThread = GetThreadDesktop(Thread.CurrentThread.ManagedThreadId)
        originalInput = OpenInputDesktop(0, False, DESKTOP_SWITCHDESKTOP)
 
        newDesktop = CreateDesktop("Desktop" & Guid.NewGuid().ToString(), Nothing, Nothing, 0, GENERIC_ALL, Nothing)
        SetThreadDesktop(newDesktop)
        SwitchDesktop(newDesktop)
 
        Dim newThread As Thread = New Thread(AddressOf NewThreadMethod)
        newThread.CurrentCulture = Thread.CurrentThread.CurrentCulture
        newThread.CurrentUICulture = Thread.CurrentThread.CurrentUICulture
        newThread.Start(New abcLockSystemParameters(newDesktop, background))
        newThread.Join()
 
        SwitchDesktop(originalInput)
        SetThreadDesktop(originalThread)
 
        CloseDesktop(newDesktop)
        CloseDesktop(originalInput)
 
        Return True 'Result
 
    End Function
 
    Private Sub NewThreadMethod(ByVal params As Object)
        Dim v As abcLockSystemParameters = DirectCast(params, abcLockSystemParameters)
        SetThreadDesktop(v.NewDesktop)
        Using f As Form = New BackgroundForm(v.Background)
            f.Show()
            myForm.ShowDialog()  '~~~~ Show the login screen here
            f.BackgroundImage = Nothing
            Application.DoEvents()
            Thread.Sleep(250)
        End Using
    End Sub

Looks like pretty easy one, isn't it ? But it's a tough one for me.

Can you please help me to understand this code ?

Thanks in advance...