Q146907: HOWTO: Create a Screen Saver in Visual Basic
Article: Q146907
Product(s): Microsoft Visual Basic for Windows
Version(s): WINDOWS:4.0
Operating System(s):
Keyword(s): kbsetup kb16bitonly kbVBp400 kbGrpDSVB kbDSupport
Last Modified: 11-JAN-2001
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The information in this article applies to:
- Microsoft Visual Basic Standard Edition for Windows, version 4.0
- Microsoft Visual Basic Professional Edition for Windows, version 4.0
- Microsoft Visual Basic Enterprise Edition 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
Form1.Show 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:
Q84251 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 query words:
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Keywords : kbsetup kb16bitonly kbVBp400 kbGrpDSVB kbDSupport
Technology : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB400Search kbVB400
Version : WINDOWS:4.0
Issue type : kbhowto
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