GDI+

Sub Main is the entry point into our application, the first procedure that executes when the screen-saver program is run. The STAThread attribute means this application will run in a single-threaded apartment, and it’s needed for COM interoperability reasons. Windows will pass parameters to this program whenever a user is setting up the screen saver using the Display Properties │ Screen Saver property screen. The parameters will be passed in an array named args, and Windows will pass a /p, /c, or /s argument, depending on how the screen saver should behave. We’ll explain each argument in the following paragraphs.

First we need to determine whether an argument was passed and, if so, which one. A /p argument means we’re being asked to show a preview of the screen saver. We haven’t implemented the preview functionality here because it involves creating and joining threads and is beyond the scope of this sample, so we’ll simply exit the application.

<STAThread()> Shared Sub Main(ByVal args As String())
    If args.Length > 0 Then
        If args(0).ToLower = "/p" Then
            Application.Exit()
        End If

If the screen saver should offer a form for user options, Windows passes a /c, so we’ll create and display a frmOptions form, and then exit when the form is closed. If the screen saver should simply execute normally, Windows passes a /s, so we’ll create and display a screenSaverForm and then exit when the form is closed.

        If args(0).ToLower.Trim().Substring(0, 2) = "/c" Then
            Dim userOptionsForm As New frmOptions()
            userOptionsForm.ShowDialog()            Application.Exit()
        End If
        If args(0).ToLower = "/s" Then
            Dim screenSaverForm As New frmSceenSaver()
            screenSaverForm.ShowDialog()            Application.Exit()
        End If

If there are no arguments, we’ll simply execute the screen saver normally, because it means that the user double-clicked the .scr or .exe file or ran it from within Visual Studio. We know this because otherwise Windows would have passed a parameter to the application.

    Else
        Dim screenSaverForm As New frmSceenSaver()
        screenSaverForm.ShowDialog()        Application.Exit()
    End If
End Sub

When the screen-saver form is loaded, we initialize it by creating the Graphics object we’ll use for drawing, loading the user’s saved options (creating an options file if one does not exist), setting the speed based on the user-defined options, and enabling the timer. The speed setting dictates how quickly shapes will be displayed when the screen saver is active.

Private Sub frmSceenSaver_Load(...
    m_Graphics = Me.CreateGraphics()
    m_Options.LoadOptions()    Select Case m_Options.Speed
        Case "Slow"            Me.tmrUpdateScreen.Interval = 500
        Case "Fast"            Me.tmrUpdateScreen.Interval = 100
        Case Else
            Me.tmrUpdateScreen.Interval = 200
    End Select
    Me.tmrUpdateScreen.Enabled = True
End Sub

All subsequent operations are in response to events. When the timer ticks, a new shape is drawn on the screen, and this continues until a mouse button is clicked or the mouse is moved over the form.

Private Sub tmrUpdateScreen_Tick(...
    DrawShape()End Sub

The DrawShape subroutine draws a randomly colored, randomly sized shape to the screen, based on some user-defined parameters. It starts by computing the largest possible values for the screen, as indicated by the form width and height. (Remember that the form is maximized.) Note that x1, x2, y1, and y2 are coordinates for random points to be generated later, myRect is the rectangle within which the shapes will be drawn, and myColor is the color to be used to draw the shapes.

Private Sub DrawShape()
    Dim maxX As Integer = Me.Width    Dim maxY As Integer = Me.Height    Dim x1, x2, y1, y2 As Integer
    Dim myRect As Rectangle
    Dim myColor As Color

Next we generate some random numbers ranging between zero and the maximums we determined earlier, and we create a rectangle based on the generated coordinates.

    x1 = m_Random.Next(0, maxX)
    x2 = m_Random.Next(0, maxX)
    y1 = m_Random.Next(0, maxY)
    y2 = m_Random.Next(0, maxY)
    myRect = New Rectangle(Math.Min(x1, x2), Math.Min(y1, y2), _
        Math.Abs(x1 - x2), Math.Abs(y1 - y2))

We’ll select a color at random for the shape we’re about to draw. If the user wants transparent shapes, we’ll allow the transparency to be randomly generated as well. If not, we’ll set the Alpha to 255 (the maximum). Alpha, which is the first argument to the Color.FromArgb function, determines how opaque the shape will be.

    If m_Options.IsTransparent Then
        myColor = Color.FromArgb(m_Random.Next(255), m_Random.Next(255), _
            m_Random.Next(255), m_Random.Next(255))
    Else
        myColor = Color.FromArgb(255, m_Random.Next(255), _
            m_Random.Next(255), m_Random.Next(255))
    End If

Finally, we draw an ellipse or rectangle based on user-defined options.

    If m_Options.Shape = "Ellipses" Then
        m_Graphics.FillEllipse(New SolidBrush(myColor), myRect)
    Else
        m_Graphics.FillRectangle(New SolidBrush(myColor), myRect)
    End If
End Sub

When the user clicks a button or moves the mouse, we want the screen saver to quit. The following routines accomplish that. The first one simply exits if any mouse button is clicked on the screen saver form.

Private Sub frmSceenSaver_MouseDown(...
    Application.Exit()End Sub

The second one responds to a mouse movement. Because the MouseMove event can sometimes be fired by very trivial moves of the mouse, we’ll verify that the mouse has actually been moved by at least a few pixels before exiting. To do that, we store the current location of the mouse, turn on a switch that shows we’re tracking the mouse movements, and exit only if the mouse has been moved at least 10 pixels.

Private Sub frmSceenSaver_MouseMove(...
    If Not m_IsActive Then
        Me.m_MouseLocation = New Point(e.X, e.Y)
        m_IsActive = True
    Else
        If Math.Abs(e.X - Me.m_MouseLocation.X) > 10 Or _
            Math.Abs(e.Y - Me.m_MouseLocation.Y) > 10 Then
            Application.Exit()
        End If
    End If
End Sub

We want the user to be able to choose screen-saver options such as how fast shapes should be drawn on the screen, whether they should be rectangles or ellipses, and whether the shapes should be transparent. So we provide an Options form, which gets called when the screen-saver program is invoked with the /c argument.

We’ve defined a class named Options (which you can see in Options.vb) to hold the preferences as properties and provide methods for loading and saving the preferences. Creating a class makes it easy to save the options to disk in XML format by serializing the class and then later retrieving them by deserialization. (See “Application #82: Serialize Objects” for more details.)

The btnOK_Click procedure in frmOptions creates an Options object and sets its values to the user-selected values on the form. It then saves the choices to disk.

Private Sub btnOK_Click(...
    Dim myOptions As New Options()    If Me.optEllipses.Checked Then
        myOptions.Shape = "Ellipses"
    Else
        myOptions.Shape = "Rectangles"
    End If
    myOptions.IsTransparent = Me.chkTransparent.Checked
    myOptions.Speed = Me.cboSpeed.Text
    myOptions.SaveOptions()    Me.Close()
End Sub

The Form_Load event procedure of frmOptions loads the current user-defined options and sets the controls on the form accordingly. The Load method of the Options class always returns values, even if the options file doesn’t currently exist.

Private Sub frmOptions_Load(...
    Dim myOptions As New Options()    myOptions.LoadOptions()
    Me.cboSpeed.Text = myOptions.Speed    Me.chkTransparent.Checked = myOptions.IsTransparent    If myOptions.Shape = "Ellipses" Then
        Me.optEllipses.Checked = True
    Else
        Me.optRectangles.Checked = True
    End If
End Sub