ZX Computings - OpenLibra

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