The program starts from a Main subroutine. That routine examines the command line parameters for the flags /p, /c, and /s.

/p

The screen saver should display as a preview. The second command line argument gives the hWnd (window handle) of the preview window in which the program should draw the preview.

/c

The screen saver should display a configuration screen. This program displays the frmConfig form as a modal dialog and then exits.

/s

The screen saver should run as a normal screen saver. The program also runs in this mode if it receives no command line flag or some other flag. To display as a normal screen saver, the program displays the frmCanvas form as a modal dialog.

Public Enum ActionType
    actConfigure
    actPreview
    actRun
End Enum

Sub Main(ByVal args As String())
    Dim frmMain As New frmMain
    Dim frmOption As New frmOptions

    If VerifySettingsFile() Then
        LoadSettings()
    Else
        Application.Run(frmOption)
        Exit Sub
    End If

    'get our arguments
    If args.Length = 0 Then
        action = ActionType.actRun
    Else
        Select Case args(0).ToLower
            Case "/p"
                action = ActionType.actPreview
            Case "/c"
                action = ActionType.actConfigure
            Case "/s"
                action = ActionType.actRun
        End Select
    End If

    'process our request
    Select Case action
        Case ActionType.actConfigure
            Application.Run(frmOption)
        Case ActionType.actPreview
            SetForm(frmMain, args(1))
            Application.Run(frmMain)
        Case ActionType.actRun
            Application.Run(frmMain)
    End Select
End Sub

When invoked in screen saver mode, the program displays frmMain.

When invoked for preview, the program calls subroutine SetForm and then displays frmMain. Subroutine SetForm reparents the form into the preview window. (This process is impressively awkward. Perhaps they'll streamline this a bit in the next major release of Windows. Then we can learn how to do it all over again!)

Private Sub SetForm(ByRef f As Form, ByRef arg As String)
    Dim style As Integer
    Dim previewHandle As Integer = Int32.Parse(CType(arg, _
        String))
    Dim corners As New Win32Corners
    Dim r As New Win32Corners.RECT

    'get dimensions of preview
    corners.GetClientRect(previewHandle, r)

    With f
        .WindowState = FormWindowState.Normal
        .FormBorderStyle = FormBorderStyle.None
        .Width = r.right
        .Height = r.bottom
    End With

    'get and set new window style
    style = corners.GetWindowLong(f.Handle.ToInt32, _
        corners.GWL_STYLE)
    style = style Or corners.WS_CHILD
    corners.SetWindowLong(f.Handle.ToInt32, _
        corners.GWL_STYLE, style)

    'set parent window (preview window)
    corners.SetParent(f.Handle.ToInt32, previewHandle)

    'save preview in forms window structure
    corners.SetWindowLong(f.Handle.ToInt32, _
        corners.GWL_HWNDPARENT, previewHandle)

    corners.SetWindowPos(f.Handle.ToInt32, 0, r.left, 0, _
        r.right, r.bottom, _
        corners.SWP_NOACTIVATE Or corners.SWP_NOZORDER Or _
            corners.SWP_SHOWWINDOW)
End Sub

' Draw the image as large as possible without distortion.
Private Sub DrawTheImage()
    Dim PanelGraphic As Graphics = pnlImage.CreateGraphics
    PanelGraphic.Clear(Color.Black)
    Try
        If intLast = sFiles.GetLength(0) Then intLast = 0
        Dim newImage As Bitmap = _
            Bitmap.FromFile(sFiles(intLast))

        Dim x As Integer
        Dim y As Integer
        Dim wid As Integer
        Dim hgt As Integer
        If (newImage.Height / newImage.Width) > _
            (pnlImage.Height / pnlImage.Width) Then
            ' The new image is relatively tall and thin.
            ' Make the image as tall as possible.
            hgt = pnlImage.ClientSize.Height
            wid = CInt(hgt * newImage.Width / _
                newImage.Height)
        Else
            ' The new image is relatively short and wide.
            ' Make the image as wide as possible.
            wid = pnlImage.ClientSize.Width
            hgt = CInt(wid * newImage.Height / _
                newImage.Width)
        End If

        x = (pnlImage.Width - wid) \ 2
        y = (pnlImage.Height - hgt) \ 2
        PanelGraphic.DrawImage(newImage, x, y, wid, hgt)

        newImage.Dispose()
        PanelGraphic.Dispose()
        intLast += 1
    Catch ex As Exception
        DrawErrorImage()
    End Try
End Sub

Private Sub Form1_KeyDown(ByVal sender As Object, ByVal e _
    As System.Windows.Forms.KeyEventArgs) Handles _
    MyBase.KeyDown
    Application.Exit()
End Sub

Private Sub pnlImage_MouseMove(ByVal sender As Object, _
    ByVal e As System.Windows.Forms.MouseEventArgs) Handles _
    pnlImage.MouseMove
    Static done_before As Boolean
    Static mouse_x As Long
    Static mouse_y As Long
    If Not done_before Then
        done_before = True
        mouse_x = e.X
        mouse_y = e.Y
    Else
        If Math.Abs(e.X - mouse_x) > 10 Or Math.Abs(e.Y - _
            mouse_y) Then
            Application.Exit()
        End If
    End If
End Sub

Tip

In a program such as this one that reads command line parameters, it is handy to test the program with different parameters. In this example, you can test the program with the /c parameter.

It's a real hassle, however, to have to compile the program and then launch it from a shortcut or DOS window so you can pass it different parameters. Fortunately you can make the development environment start the program with command line parameters.

In Project Explorer, select the project. Then select the View menu's Property Pages command.

Click the Configuration Properties category and select Debugging. Enter the parameters you want to use in the "Command line arguments" text box.

Note

To install the screen saver, compile the program into an executable file. Change the file's extension from .exe to .scr and copy it into the system directory. That's all you need to do.