ZX Computings - OpenLibra

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Paul writes to ZX Computing:
"A short while ago I was
writing a 'space war' type of
program with a starry sky, and
moving the space ships by printing
black squares over them
which meant that as the game
progressed all the stars disappeared.
"I was trying to find a way
around this when a friend lent
me his "Programming the
Z80", by Rodnay Zaks. This
helped me to write the following
machine code program:
Id hl,7530h (300001
Id de, (d-file)
inc de
Id be, 02D6 (726)
LDIR
Ret
"This program loads what is
above memory location 30000
into the display, and by changing
over the de and hi registers it
saves the display above
30000. This meant that when I
printed out my sky I used one
routine to save it, then used the
other as a type of CLS, but
recalling the same background
zap
Paul Gausden from
Kingswood brings a little
machine code into play to
put you in the cockpit of
a biplane engaged in a
deadly battle over the
straits of Mallacash.
each time, so now the stars
stayed where they were!
"One of the programs I've
written using this routine is
ZAP. It uses the routines to
save the foreground (the interior
of the cockpit) and recalls
it each time. You are chasing
after an enemy aircraft and you
have to remember the controls
work in reverse.
"To get the GOSUBs in the
REM statements, type THEN
GOSUB and rub out the THEN."
As you can see from the
screen printout, the enemy
plane is the little thing you can
see through the cockpit. It
moves randomly around, and
you must use 5,6,7 and 8 to
move yourself into a position
where the enemy plane will be
on the cross of your sight. As
Paul pointed out, you have to
remember that you are, in
effect, moving backwards,
swinging the view of the enemy
against the sky. This may
sound complicated, but it
becomes very clear once you
RUN the program, and gives a
good impression of a dogfight.
X"
16K Games
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POKE 1 6 5 1 3 , 9 1
POKE 15539,117
1 REM 5K7 GOSUB ?£RND