4-15-93

This program is for demo purposes only, I do not want you to send me
any money.  I just want to share a program I had fun writing.  This
program was fun to me in that it was possible to do a windows 3.1
screen saver entirely in visual basic and windows calls without
additional DLLs required.

This is a screen saver written in visual basic 2.0 (standard
edition).  The program actually cycles between several different
screen savers within the same program to give quite a bit of
variety.  This program is based on an example in "Learn Programming
and Visual Basic 2.0" by John Socha and Sybex Inc.

Most of the savers work by starting at random positions with zero
velocity and acceleration vectors.  Then each time through a random
acceleration is added to the velocities.  When an object gets to the
edge of the screen the velocities sign is set to bring it back into 
screen which then looks to the user as if the object bounced off the
edge of the screen.  Also when the velocity reaches a certain limit,
the velocity is set to zero to prevent things from getting too out
of hand.

The grabbing of the desktop pixels was based on Jonathan Zuck's 
screen-capture utilities in the November issue of Windows Tech 
Journal.  The desktop animation is done by using the windows DLL
'BitBlt' and experimenting using the BC++ reference guide (not the
best source).

Disclaimers:    I have no idea what the side effects of this program
may be on your system.  The program is provided as an example at no
charge.  I am not a windows expert, and the program is provided as is
without any warranties or obligations.

This program was developed on a 386/40MHz clone with a JDR VGA 1024+ 
card (ET4000 based) using Visual Basic 2.0 (therefore the saver needs
VBRUN200.DLL to run).  The line drawings are fast enough on this
machine, but the screen rolling tends to be jerky at the faster
speeds.

Lessons Learned:

Application Title must start  with 'SCRNSAVE' and has maximum length
     that is recognized.

I was using a VB clock program that while minimized would change 
     caption to show time.  For some reason changing the caption
     would prevent windows from calling the screen saver.

In the windows desktop, I set timeout interval before saver is called 
     to 1 minute for testing.  I found that the display got slower 
     and slower.  Then when I would move the mouse, the display
     would change many times before returning to windows.  It seems
     that windows was calling another instance of the program every
     minute.  I don't know why this is, but to fix the problem the
     program now checks for previous instances when it starts up,
     and then quits if another instance is already running.

PS -- even though I have Borland C++ and am a C programmer, I much
     prefer the visual basic development environment for forms,
     debugging, etc.


     Bruce McLean
     800 S. HW. 1417 #1214
     Sherman TX 75090
     CIS: 71413,2664