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Th» simple little program, quite apart from enabling one to draw pretty picture* on the screen of one's ZX80, shows how you can control on-screen movement. You can change the symbol in use and the direction in which you are moving st any time during the program execution. Instructions and Variables When the program is RUN an asterisk (star) it displayed on the screen. To alter the symbol in use press '5' then 'NEWLINE' followed by the code of the required symbol and 'NEWLINE'. Changes in the direction of movement can be made by keying the desired direction code ( see Fig. 1.) and the inevitable 'NEWLINE' The program uses the following variables: D C A I - Position on-screen of current symbol. Code of displayed symbol. Direction code. Dummy variable. Games zx Drawing Board Sample Program 1 REM "5KETCHPPD 5 FR5T 6 FOR N =0 TO 63 7 PLOT N., 4-3 8 PLOT N,O 9 NEXT N 10 FOR P =0 TO 4-3 11 PLOT 0.P 12 PLOT 63,P 13 NEXT P 15 5LOU 20 LET X = 32 30 LET Y = 22 40 GOSUB 500 50 UNPLOT X,Y 60 PLOT X J Y 70 GOTO 4-0 80 GOSUB 500 90 GOTO 80 100 GOSUB 500 110 PLOT X,Y 120 UNPLOT X,Y 130 GOTO 100 500 IF INKEY*= «« ^ M 510 IF INKEY $ = ** 2 " 520 IF INKEY%= 530 IF INKEY$= "0" THEN 540 IF INKEY $ = " 5 " THEN 550 IF INKEY$= "6" 560 IF INKEY%- *A M 570 IF INKEY "Q" 590 RETURN Try the following data string, the '/* represents the NEWLINE. A) 5/128/8/4/2/2/4/4/2/2/2/2/6/6/2/6/8/6/6/6/6/6/ f 6/2/6/8/6/6/8/4/8/8/8/8/8/6/8/4/4/4/2/2/2/4/4/ £ 4/4/4/4/8/8/8/5/8/9/9/9/9. qq 4 + 6 GOTO 40 GOTO GOTO 600 GOTO 100 LET X = X — THEN LET Y=Y- THEN LET Y =Y + THEN LET X=X + 10 70 80 90 100 110 120 130 140 150 160 170 LET D = 310 LET C = 20 FOR I = 1 T.O 640 PRINT" "; NEXT I 50 FOR N=0 TO 100© POKE PEEKH6396) + 256'PEEK( 16397) + D,C INPUT A IF A= 1 THEN LET D = D + 32l IF A = 2 THEN LET D = D + 3S IF A = 3 THEN LET D = D + 34 IF A = 4 THEN LET D = D-1 I IF A = 6 THEN LET D = D + 1 IF A = 7 THEN LET D=D-3if IF A = 8 THEN LET D = D-33| IF A = 9 THEN LET D = D -321 IF A = 5 THEN INPUT C GOTO 60 From Kowloon, Hong Kong. H. Hugh McAllum show* ut a few tricks with the ZX printer H.H.H.1982 M T * = J W T tRND*22) +10 70 LET Y=INT IRND*22) 80 IF X +Y
Etchasketch This very short program allows you to use the keys "5", "6", "7" and "8" to move the PLOT blob around the screen, drawing pictures of your choice. Once you've got it running, try and modify it to (a) give you a choice of starting position; and/or (b> 'turn off' the blob from time to time tomove it to a new position on the screen without leaving a trail. 10 LET FI=URL "1" 20 LET B 30 LET fi$=INKEY$ 4-0 IF = THEN GOTO 30 60 LET (fl$="7")- 70 LET B=B + (P$ = "8") 80 PLOT 100 GOTO 30 Keep this handy reference guide to aid you when programming your ZX81 Symbol Code How obtained 0 • or • SPACE 1 0 shifted 1 2 0 shifted 2 3 0 shifted 7 4 0 shifted 4 5 0 shifted 5 6 0 shifted T 7 0 shifted E R=5H •••••••• m 10 8 128 129 130 131 132 0 shifted A 0 shifted D 0 0 shifted S SPACE 0 shifted Q 0 shifted W 0 shifted 6 shifted 0 R O H 133 Symbol Code How obtained 0 shifted 8 134 0 shifted Y 135 0 shifted 3 136 0 shifted H 137 0 shifted G 138 0 shifted F 91
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j Summer Britain's Biggest Magazine
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ZX 80/81 HARDWARE/SOFTWARE ZX KEYBO
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ZX Computing is published quarterly
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16K-byte RAM pock for massive add-o
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The @*?$1!&£@ RAM pack Dear ZX Com
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I u < o •0 8 & £T © Benchmarks
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1 1© L" 20 30 IN5 5 0 60 80 9C 100
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The Explorer's Guide to the ZX81 IF
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Orbit S M King from Bristol takes y
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Page 93 and 94: meant the addition to its repertoir
Page 95 and 96: SYSTEM/MULTIFUNCTION COMMANDS BREAK
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Page 99 and 100: Make sure you get every issue of ZX
Page 101 and 102: ZX80 Programs ZX80 fights back Musi
Page 103 and 104: Catch Avoid being trapped by your s
Page 105 and 106: Software Orwin strikes again Casset
Page 107 and 108: ZX81 Software LARGE CHARACTERS REM
Page 109 and 110: Moving graphics Getting into the Mo
Page 111 and 112: Specialist Book§ i Choosing progra
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Page 131 and 132: ZX Users' Club JOIN YOUR USERS' GRO
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