Invaders 1978 v1.0


    ##     The Invaders march ...
   ####      Bom bom bom bom ...
  ######       Left, right, fire!
 ## ## ##        Faster, faster they march ...
 ########          Suddenly you're 11 again!
   #  #              Dodge the bombs ...
  # ## #               They're turning green ...
 # #  # #                Get them before they land!


A version of Taito's original Space Invaders(TM) for the PC

James Eibisch, June 1996

jeibisch@revolver.demon.co.uk
http://www.revolver.demon.co.uk/


********** BORING STUFF

This game is mailware. That is, it's free to use and distribute, but
I'd appreciate a quick email from you if you like it. This isn't so I
can junk mail you later (believe me, I *hate* people who do that), but
so I can gauge how well it travels.

Feel free to distribute it anywhere you like, but only on condition that
you keep the two files (INV78.EXE and INV78.TXT) together and that you
don't charge any payment for it.


********** 	PLAY THE GAME

Type "inv78" at the DOS command prompt.

Left         - Left CTRL
Right        - Left ALT
Fire         - Right SHIFT
Stop program - Esc


********** INTRO

Having tried a number of Space Invader 'clones' for the PC I decided to
write one that was actually something like the original - most of the
'clones' are not! My interest in the game is just nostalgia - playing
Taito's Space Invaders around 1979, aged 11, was my introduction to
computers. It seemed magical to me, and I was fascinated from that point
on in working out how an inanimate object comprising a bunch of
electronics, some memory, a VDU, and some input controls could offer
such unlimited possibilities. So, 17 years after first grappling with a
computer game, here's my little tribute to it and to the company who made
it.


********** REQUIREMENTS

Requires:
---------

DOS - tested with MS-DOS 6.22 and Windows 3/95. No known lower limit.
VGA - tested with ET4000 and ET6000 cards (uses screen 13: 320x200x256)

Supports:
---------

Soundblaster - tested with AWE32

Uses ports:
-----------

&H3DA - for vertical retrace

&H388
&H389 - for Adlib sound

&H3C6
&H3C8
&H3C9 - for palette setting

Uses memory locations:
----------------------

&H417 - to read the keyboard

Machine speed requirements:
---------------------------

Should run at full speed on any x86 processor.

When interpreted, rather than compiled, the program does all its work
within 15% of the vertical retrace cycle on a 486DX/66. The compiled
version should keep up with the vertical retrace on an 8086.

There's a secret key (excitement!) that will display how much of the
vertical retrace time the game takes up each cycle.

Unknown requirements:
---------------------

Base memory - tested with 479K free base memory
Memory manager - tested with himem.sys and emm386.exe


********** NOTES

1. The program does not attempt to detect a soundcard; it assumes a
Soundblaster is installed. I've tried it on one machine without a
soundcard and it worked fine, but can't guarantee it'll work on yours.

2. The player's bullet fire and explosion sound effects are pretty
dismal. I've found no information on how to use white noise on the
Soundblaster, so the program approximates with the tone channels. If you
know how to do white noise on the SoundBlaster, please let me know!

3. The attract mode is minimal. I might add the original attract and
demo modes in the future.

4. The program does not use the original rules for determining saucer
scores.

5. The program simulates a monitor 256 pixels wide, as per the original.
The background colour for this is set to a dark grey to attempt to
simulate a little bit of monitor wear and burn-in. I found the jet black
of a modern PC monitor was not quite authentic enough :-) If you cannot
see the grey background, try increasing your brightness and contrast
controls.

6. Quake it ain't. It's just a nostalgia trip.