Hello everyone,

 

The Game of Life is one of my favorite topics and is the forerunner

of modern Cellular Automation, Evolutionary Algorithms, Fractals and

Mandlebrot graphics

 

The ZX81 GAME of LIFE was based on John Conway's article in

Scientific American where he described a virtual reality of cells battling

for survival visible on a computer screen. A few simple rules cause

cells to form dynamic colonies which eat or are eaten by competing

colonies. Some colonies evolve and some are steady state. Some move

and some are static

 

The 2 rules of the GAME of LIFE state that:

 

An existing cell survives if surrounded by 2 or 3 neighbors

A new cell is born if surrounded by 3 neighbors

Under all other conditions a cell will die of either of

loneliness or overcrowding.

 

To conserve memory the ZX version of LIFE uses the screen

both for memory and display. To do this we generate two intermediate

cell states of dying and birth on the screen before executing the rule.

 

The left and right walls have fixed pattern templates, which make

life interesting and the top and bottom of the screen are stitched

together (it's a closed universe!)

 

GOODLIFE.P  is  a particularly prolific ZXLIFE pattern which

will run for 10,000s of generations. It will run right after loading

as it was captured by the Save command.

 

As the screen is used to store the pattern this is the only way to

save it. If you break the program the pattern is lost and you will

need to reseed the screen. 

 

This is the reason I have added this "S" command so that you

save a LIFE in progress (to TSLIFE.P) . Rename the file after

saving and I am still looking for the BESTLIFE pattern so let me

know if you capture a truly immortal non-repeating pattern.

 

Try using a diffuser, just a piece of translucent paper, in front of

the monitor screen, to softens the LIFE contours and it resembles a

colony of bacteria or weather patterns.

 

The ZX81 BASIC and ML program is found here: GOODLIFE.P

 

The term GOODLIFE was used in a SF by Fred Saberhagen called

Beserker Base. The Beserkers, a race of run-a-muck robots bent

on destroying all organic life in the galaxy, used that name to

identify any human or member of other organic species who in

exchange for sparing their own life were willing to cooperate.

It suggest that self perpetuating inorganic life forms may be

coerced to do the same on our behalf.

 

While running the program: adjust the speed with the 0-9 keys.

The S key saves a snapshot of the game in TSLIFE.P

The R key breaks and randomizes the screen and walls after

selecting the cell density.

 

The C key starts the COMPOSE mode controlled with the

following key functions:

 

W –white background

B – black background

5,6,7,8 - move the cursor N, S, E, W

1,2,3,4 - move cursor diagonally

9 - pen down

0 - pen up

N/L – RUN

 

Use slow emulation to control cursor speed.

 

You can break and list the BASIC program lines to view the

how the BASIC shell performs the above functions as well  

Initialization and Saving snapshots.

 

The ML program runs the Game of Life algorithm on the ZX 81

screen contents. It uses a clever scheme of marking cells a grey

color for dying and for birth as intermediate steps quite visible in

slow emulation.

 

There are different features visible at different speeds. This program

still blows me away after all these years especially when run at high

speed.

 

The key to long life are the templates on the left and right walls which

are very "prolific" and although one wall sometimes "freezes" the other

wall will fire it up again by bombarding it with it's "spawn".

 

Without these templates such a small universe would normally quickly

expire. With the right template pattern this Tiny GOL universe is capable

of infinite variation.

 

GOODLIFE  as such is not perfect and still freezes after tens of

thousands of generations when both walls stop producing simultaneously

I think four template walls would make ZX LIFE run indefinitely without

freezing.

 

The template idea is something new (I think)  and reminds me of

theories of clay  substrates forming the basis for the evolution of early

life on earth.

 

ZXLIFE runs great under EightyOne or Xtender or any other emulator

and of course runs fine but slow on the real thing.  No special video

routines are used and the resolution is typical of the ZX plot routines.

 

The annotated ML program is listed here.

 

                   ;The ZX81 GAME of LIFE by wilf rigter @ 1983

                   ;based on Conway's article in Scientific American

 

                                        ;origin is 4084h

                LD HL,(400C)      ;HL points to the top of the screen memory

                LD DE,0021        ; -/+ 33 bytes to move up/down

                LD C,14             ;22 lines

NLINE        INC HL               ;first cell

                LD B,1E             ;30 cells per line

 

NCELL        LD A,50             ;initialize cell counter in A with 50h

                CP (HL)              ;this part checks block of 8 neighboring cells

                ADC A,D             ;increments ">80h" neighbor counter in A

                INC HL               ;top middle

                CP (HL)

                ADC A,D

                INC HL               ;top right

                CP (HL)

                ADC A,D

                ADD HL,DE         ;right

                CP (HL)

                ADC A,D

                ADD HL,DE         ;bottom right

                CP (HL)

                ADC A,D

                DEC HL              ;bottom middle

                CP (HL)

                ADC A,D

                DEC HL              ;bottom right

                CP (HL)

                ADC A,D

                SBC HL,DE          ;left

                CP (HL)

                ADC A,D

                INC HL               ;middle cell

                CP (HL)

                JR NC 06            ;if middle cell is >56

                CP 55

                JR NZ 0C

                LD (HL),88         ;mark for birth

                CP 55

                JR Z 06

                CP 56

                JR Z 02

                LD (HL),08         ;mark as dying

                XOR A

                SBC HL,DE

                DJNZ NCELL

 

                INC HL               ;advance to the next line

                INC HL               ;skip EOL character

                DEC C                ;dec line counter

                JR NZ  NLINE      ;last line?

 

                                        ;now screen memory is tested for

                                        ;dying and birth marks

 

                                        ;first execute dying cells

 

                LD DE,0880        ;dying mark in D and death in E

 

MARK        LD HL,(400C)      ;top of screen

                LD BC,03B4        ;cell counter

NMARK      INC HL               ;first cell

                LD A,(HL)           ;test cell

                CP D                  ;is it marked cell? ie CHR$ 08

                JR NZ NODIE      ;skip if not marked

                LD (HL),E           ;finish the birth/death cycle

NOMRK      DEC C                ;dec cell counter

                JR NZ NMARK      ;next cell

                DEC B                ;next cell

                JR NZ NMARK      ;next cell

 

                                        ;the same routine is used for birth

                XOR A               ;now execute the birth cycle

                CP E                  ;did we already do the births?

                JR Z END            ;If birth and death done then bye

                LD DE,8800        ;birth mark in D and birth in E

                JR MARK            ;go forth and deliver

 

END          LD C,20             ;it's a closed universe

                SBC HL,BC          ;so the last line (32 chars)

                LD DE,(400C)      ;is copied to the top line

                LDIR                  ;while the top line is copied

                EX DE,HL           :to the bottom line thereby

                LD C,21             ;stitching the top and bottom

                LDIR                  ;of the screen together like

                RET                   ;a cylinder

 

 

 

 

 

 

     

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