How To Create a Screen Saver in Visual Basic

[ben2ong2]

PRODUCT :Microsoft Visual Basic for Windows
PROD/VER:4.00
OPER/SYS:WINDOWS
KEYWORDS:kbprg kbcode

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The information in this article applies to:

- Standard, Professional, and Enterprise Editions of Microsoft
  Visual Basic, 16-bit, for Windows, version 4.0
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SUMMARY
=======

You can create a Windows screen saver with Visual Basic by following the
guidelines listed below. However, please note that this article gives only
a very rough outline of what you should do for a robust screen saver. These
are general guidelines only.

MORE INFORMATION
================

Follow these guidelines when creating a Windows screen saver with Visual
Basic:

- In the File Make EXE File dialog, insert the string SCRNSAVE: (in
   upper case) at the beginning of the Application Title. For example:

   SCRNSAVE:Flying Fish.

- In the File Make EXE File dialog, specify the program file name
   extension as .SCR instead of .EXE.

- Locate the .SCR program file in the \WINDOWS directory.

- Give your form the following property settings so that it
   occupies the entire screen and does not have a title bar:

      Caption     = ""     (no caption)
      ControlBox  = False
      MaxButton   = False
      MinButton   = False
      WindowState = 2      (maximized)

- Add code to all MouseMove, MouseDown, and KeyDown event handlers
   that exit the program. Because Visual Basic may invoke the MouseMove
   event when the form is first loaded, you must write code to ignore
   the first MouseMove event. The following MouseMove code avoids an
   artifact event that occurs when the application is first activated or
   when the application is running and another instance starts (causing
   loss of focus) and then quits (restoring focus):

      Private Sub Form_MouseMove (Button As Integer, Shift As Integer, _
         X As Single, Y As Single)
         Static count As Integer
         If count > 2 Then
            End
         Else
            count = count + 1
         End If
      End Sub

   This gives you a bit of slack when it comes to artifact MouseMove
   events. You will want to do something similar with the MouseDown and
   KeyDown events.

Preventing Multiple Launches
----------------------------

Windows usually launches the screen saver program multiple times. To
prevent more than one copy of your screen saver from running, add the
following statements to the Form_Load event handler, or Sub Main if used:

   Private Sub Form_Load ()
      If App.PrevInstance Then
         End
      End If
   End Sub

There is no reason to attempt to restore the previous instance of the
screen saver as the active window because it will become the active window
when the new instance ends. All you have to do is terminate when you see
another instance running.

To prevent multiple instances of the application from running as well as to
keep the application running, you should move the code from the Form_Load()
to a Sub Main(). Then set the project's Startup Form Option to Sub Main().
Setting the project to begin processing at Sub Main is done on the Project
tab which is part of Options... under Tools menu. For example:

   Public Sub Main ()
      If App.PrevInstance Then   ' If already running, end the application.
         End
      Else
         You are not allowed to view links. Register or Login 1             ' Show the screen saver form.
      End If
   End Sub

Launching the Screen Saver
--------------------------

Windows takes care of launching the Screen Saver. It keeps track of system
idle time and launches the screen saver program. You can use a timer
control to periodically draw graphics on the form.

Screen savers are selected and configured from Windows Control Panel in
the Desktop dialog. The screen saver section of this dialog has a button
labeled Setup that invokes the screen saver program with the command
line option /c. When your program is invoked with this option, you can
display a configuration form to allow the user to select settings such
as speed, number of objects, colors, and so on. Detect the /c command line
parameter by checking the Command$ function. For example:

   Private Sub Form_Load ()
      If Command$ = "/c" Then
         frmConfig.Show   ' Display configuration form.
         Unload Me        ' Bypass regular form.
      End If
   End Sub

When Windows launches the screen saver, it usually specifies the command
line option /s.

Possible Improvements
---------------------

You may also want your program to appear on top of all other windows by
making it a TOPMOST window.

For additional information, please see the following article(s) in the
Microsoft Knowledge Base:

   ARTICLE-ID: Q84251
   TITLE     : How to Create a Topmost or Floating Window in Visual Basic

Also, you can find two example programs and a complete explanation showing
how to write your own screen savers in Visual Basic in the following book:

   "Visual Basic Workshop 3.0" by John C. Craig, published by Microsoft
   Press.

This article is a rough outline of what you should do for a robust screen
saver. For example, you might want to have the startup be a Sub Main() in
which you check for a previous instance and End if there is one. This would
avoid the form load totally if there were already an instance running. It
might also avoid the artifact MouseMove problem.

Additional reference words: 4.00 vb4win vb416
KBCategory: kbprg kbcode
KBSubcategory: APrgOther


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