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Loadstar 17
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game design.1
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2022-08-26
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╟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 >---