Loadstar 17/017.d81/game design.1

Text File | 2022-08-26 | 5KB | 319 lines

       ╟AME ─ESIGN ON THE 64
     ╨ART 1:  ├USTOM ├HARACTERS
          BY ╥OBERT ┴LONSO



  ╔N THIS FIRST OF A FIVE-PART SERIES,

YOU WILL LEARN HOW TO DESIGN ONE-COLOR

AND MULTI-COLOR CUSTOM CHARACTERS AND

USE THEM IN YOUR PROGRAMS.

  ├USTOM CHARACTERS ARE PERHAPS ONE OF

THE MOST NECESSARY INGREDIENTS FOR

CREATING ARCADE-STYLE GAMES ON A HOME

COMPUTER.  ╔T'S INCONCEIVABLE TO

PROGRAM A ╙PACE ╔NVADER-TYPE GAME OR

ANY OTHER SPACE GAME USING LETTERS AS

ALIENS.  ╔T WOULDN'T BE VERY EXCITING

TO PLAY OR EVEN LOOK AT.  ├USTOM

CHARACTERS ARE LETTERS THAT HAVE BEEN

REDESIGNED TO LOOK LIKE ANY TYPE OF

CREATURE OR SPACE VEHICLE THAT YOU CAN

IMAGINE.  ╘HE ├OMMODORE 64 ALLOWS YOU

TO EASILY REDEFINE CHARACTERS FOR

GAMES OR FOR JUST ABOUT ANY OTHER

PURPOSE YOU MAY HAVE IN MIND.

  ├REATING CUSTOM CHARACTERS ON THE 64

IS A MATTER OF KNOWING WHERE THE

ORIGINAL CHARACTER SET IS LOCATED IN

╥╧═, WHERE YOU WOULD LIKE TO PLACE IT

IN ╥┴═ MEMORY, AND WHERE THE POINTER

THAT ENABLES YOUR NEW CHARACTER SET IS

LOCATED.  ┘OU WILL ALSO HAVE TO TURN

OFF THE INTERRUPTS AND SWITCH IN THE

╥╧═ CHARACTER SET.  ╘HEN, AFTER YOU

COPY THE CHARACTERS TO ╥┴═, YOU WILL

HAVE TO SWITCH THE CHARACTER ╥╧═ OUT

AND RE-ENABLE THE INTERRUPTS.  ┴LL

THIS SOUNDS MORE COMPLICATED THAN IT

ACTUALLY IS, SO DON'T DESPAIR.  ┘OU'LL

ALSO NEED TO KNOW A LITTLE ADDITION,

BUT THIS SHOULD NOT BE A PROBLEM.



╘URNING ╧FF THE ╔NTERRUPTS

  ╘HE FIRST STEP IS TO TURN OFF THE

KEYBOARD INTERRUPTS.  ╘HIS STEP IS

EASILY ACCOMPLISHED BY TYPING IN THE

FOLLOWING LINE:


 10 ╨╧╦┼ 56334,╨┼┼╦(56334)┴╬─254


╘HE REASON THAT THIS IS NECESSARY IS

THAT YOU WILL HAVE TO SWITCH IN THE

CHARACTER ╥╧═ IN THE NEXT STEP AND

DOING SO REQUIRES THIS FIRST STEP AS A

SAFETY MEASURE.

  ╘HE SECOND STEP IS TO SWITCH IN THE

CHARACTER ╥╧═.  ╘HE FOLLOWING LINE

DOES IT FOR YOU:


 20 ╨╧╦┼ 1, ╨┼┼╦(1)┴╬─251


╘HE ╥╧═ CHARACTER SET IS NOW IN

MEMORY LOCATIONS 53248 THROUGH 57343.

╘HIS STEP IS IMPORTANT BECAUSE

NORMALLY THESE LOCATIONS CONTAIN THE

╓╔├ ╔╔ CHIP, THE ╙╔─ CHIP, COLOR ╥┴═,

AND THE TWO ├OMPLEX ╔NTERFACE ┴DAPTERS

(├╔┴'S).

  ╔F THESE WERE LEFT IN THEIR PLACE,

YOU WOULDN'T BE ABLE TO READ THE

CHARACTER DATA.  ╘HE ├OMMODORE 64 IS

STRUCTURED WITH 64╦ OF ╥┴═ AND 20╦ OF

╥╧═ MEMORY.  ╘HE COMPUTER'S INTERNAL

BRAIN, OR ├ENTRAL ╨ROCESSING ╒NIT

(├╨╒), IS A 6510, WHICH CAN HANDLE

ONLY 64╦ OF MEMORY AT ANY ONE TIME.

╘HE 6510 USES A SOPHISTICATED APPROACH

TO SWITCHING ╥╧═ AND ╥┴═ INTO VARIOUS

SECTIONS OF HIGH MEMORY.  ╘HE LOCATION

WHICH THE SYSTEM LOOKS AT TO SEE HOW

THE MEMORY IS ORGANIZED IS MEMORY

LOCATION ONE.  ╘HIS APPROACH AT

SQUEEZING MORE MEMORY INTO A COMPUTER

IS VERY COMPLICATED AND ISN'T REALLY

NECESSARY TO DETAIL HERE.  ┴LL WE NEED

TO KNOW IS THAT TO SEE THE CHARACTER

╥╧═, THE ABOVE LINE MUST BE EXECUTED.



╥╧═ TO ╥┴═

  ╬OW YOU ARE READY TO SWITCH THE ╥╧═

IMAGE OF THE CHARACTER SET INTO A

SECTION OF ╥┴═.  ╘O KEEP THINGS

SIMPLE, IT IS ONLY NECESSARY TO COPY

THE FIRST 64 CHARACTERS.  ╘HE SECTION

OF ╥┴═ WHICH IS OFTEN RECOMMENDED FOR

AN ALTERNATE CHARACTER SET IS THE ONE

STARTING AT MEMORY LOCATION 12288 AND

ENDING AT 12799.  ╘HE PROGRAM LINE

THAT WILL DO THIS FOR YOU IS:


 30 ╞╧╥ ╪ = 12288 ╘╧ 12799:
    ╨╧╦┼ ╪,╨┼┼╦(╪+40960):╬┼╪╘


╬OW A PERFECT MIRROR-IMAGE OF THE ╥╧═

IS IN ╥┴═ READY TO BE MODIFIED, BUT

FIRST TWO THINGS MUST BE TAKEN CARE

OF.  ╘HE CHARACTER ╥╧═ MUST BE

SWITCHED OUT AND THE KEYBOARD

INTERRUPTS TURNED ON AGAIN.  ╘HESE ARE

THE TWO CLOSING STEPS:


 40 ╨╧╦┼ 1, ╨┼┼╦(1)╧╥4

 50 ╨╧╦┼ 56334, ╨┼┼╦(56334)╧╥1


┼VERYTHING IS NOW SET FOR THE CREATION

OF GOOD-LOOKING CHARACTER FORMS.


╙ETTING THE ╨OINTER

  ╘HE REASON ALL THE PREVIOUS STEPS

WERE NEEDED IS BECAUSE IT IS NOT

POSSIBLE TO WRITE (╨╧╦┼) ONTO ╥╧═

MEMORY.  ┘OU MUST HAVE THE CHARACTER

SET IN ╥┴═ TO MODIFY IT.  ┴NY ╨╧╦┼S

TO MEMORY LOCATIONS 12288 THROUGH

12799 WILL NOW AFFECT THE APPEARANCE

OF A CHARACTER.

  ╘O SEE THE NEW CHARACTER SET (IT

WILL LOOK IDENTICAL TO THE OLD ONE),

THE FOLLOWING LINE MUST BE TYPED IN:


60 ╨╧╦┼ 53272,(╨┼┼╦(53272)┴╬─240)╧╥12


╘HIS LINE SHIFTS THE CHARACTER-SET

POINTER FROM ITS ╥╧═ LOCATION TO THE

╥┴═ LOCATION STARTING AT 12288.  ╘HE

╓╔├ ╔╔ CHIP WILL NOW GET ALL OF ITS

CHARACTER DATA FROM THE ╥┴═ AREA.  ╔F

YOU HAVE BEEN TYPING IN THE LINES AS

YOU HAVE BEEN READING AND HAVE RUN THE

PROGRAM, YOU WILL NOW BE LOOKING AT

THE NEW CHARACTER SET.  ╘O EXPERIMENT

A LITTLE, YOU CAN PLACE SOME

COMMERCIAL "AT" (@) SYMBOLS ON THE

SCREEN BY TYPING THEM ON THE SCREEN.

╬OW IF YOU ╨╧╦┼ A NUMBER BETWEEN 0 AND

255 INTO MEMORY LOCATIONS 12288 TO

12295, YOU WILL SEE THE CHANGES THAT

THE SYMBOL UNDERTAKES.  ─O THIS FOR A

WHILE AND EXPERIMENT WITH THE RESULTS.

┘OU WILL PROBABLY BE SURPRISED BY THE

CRAZY EFFECTS THAT DOING SO WILL

CREATE.  ╔F YOU WANT TO FOOL AROUND

WITH THE LETTER ┴, YOU CAN ╨╧╦┼ INTO

MEMORY LOCATIONS 12296 THROUGH 12303.

╞UN, ISN'T IT?

  ╬OW THAT THE ROUTINE PART OF THE

PROCESS HAS BEEN FINISHED, YOU SHOULD

LEARN HOW TO DESIGN YOUR OWN

CHARACTERS.

  ╘HIS SMALL EXAMPLE PROGRAM IS ON

THIS ISSUE OF ╠╧┴─╙╘┴╥.  ╔F YOU WOULD

LIKE TO EXPERIMENT WITH IT NOW, PRESS
\OAD"GAME PROG-1",8
THE '\' KEY.  ┬ECAUSE OF THE NATURE OF

THE PROGRAM, IT DOES ╬╧╘ RETURN TO

╠╧┴─╙╘┴╥.  ┴FTER RUNNING THE PROGRAM,

PLEASE TURN YOUR COMPUTER OFF BEFORE

RE-ENTERING ╠╧┴─╙╘┴╥.

--< CONTINUED IN THE NEXT ARTICLE >---