PROGRAM PITSTOP
Your Sinclair, October 1991

The world's a strange place. It's full of people trying to sell
you things and telling you to cheer up. JONATHAN DAVIES knows
how to stay sane, so here are his listings ...

Blimey - it's time for another exciting foray into the world of
Program Pitstop, the bit of YS where you send in any programs you've
written and, if they're any good, I print them.

Now I'm sure you remember Mark Turner. He featured extensively in
August's Pitstop (under various pseudonyms - oops) and looks set to
become a bit of a star. He's completely taken over Pitstop this month
too, with no less than three programs. First is Screen Wrap-A-Round,
then Double Scroller and finally Interference Simulator. As they're
all so unimaginatively titled, any further explanation is rendered
useless.

So I'll let you get on with it, then.

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SCREEN WRAP-A-ROUND
by Mark Turner

It might (to the untrained ear) sound a bit boring, but type in Mark's
first program and you're sure to go into spasms of rapturous joy. What
it does is take the middle third of the screen and spin it round as if
it's drawn on a cylinder. Useless? Maybe. Jolly good fun all the same?
Definitely.

As with all this month's programs, getting it going involves the
time-honoured routine of typing in the first Basic section, saving it
onto a blank tape and then using the Hex Loader to enter the hex part,
which is then saved after the Basic. Hopefully there's room for a copy
of the Hex Loader this month as I don't think it's appeared for a
while. Remember that you only want to type in the letters and numbers
in the hex dumps (not the spaces which are only there to make things
clearer) and when you reach the end press Symbol Shift and A to stop.

When you reload the program its built-in demo routine will show you
exactly what's going on. Study it closely and you'll see that you need
to repeatedly RANDOMIZE USR 64750 to get the scrolling to work. (It's
in Line 100 - see?) The program sets aside 2048 bytes of memory to
store the bit of screen being scrolled. This is initially at address
62050, but you can change it by POKEing 64990 with something else.

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DOUBLE SCROLLER
by Mark Turner (again)

Single scrollers are old hat, let's face it, but this has to be
Pitstop's first ever double scroller. It's a bit like a single
scroller, only twice as good! As well as scrolling a normal,
double-height message across the middle of the screen, it also
superimposes a massive, huge great one over the top of it that's eight
characters high and completely different contents-wise.

There's a full demo when you run the program to indicate its potential
and show you how to get your own messages scrolling across the screen.
Note that the addresses of the two messages need to be POKEd into
64365 and 64372, and the messages themselves then need to be POKEd in
at these addresses. All should be made clear if you examine lines 35
to 70 of the program. The simplest way to achieve all this is
obviously to delete Mark's messages from the program and replace them
with your own.

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INTERFERENCE SIMULATOR
by Mark Turner (a third time)

I've printed some pretty dodgy-sounding programs in Pitstop in my
time, but this one has to take the biscuit. It simulates your Spectrum
being switched off, and the resulting fuzzy black and white dots that
appear on the screen. What's this? Has old Jonathan finally gone off
his chump? Most certainly not! The thing is, you see, that you can
restrict this effect to a certain area of the screen. Obviously this
makes the program handy for doing special effects here and there.
Great, eh?

Having typed everything in and run it you'll once again be presented
with a demo displaying the program's full capabilities. Impressive
stuff, I'm sure you'll agree. To create a bit of interference of your
own you need to POKE 63056 with the x co-ordinate, 63057 with the y
co-ordinate, 63054 with the width and 63055 with the depth of the
block you want the effect to appear in. All these values are in
character squares, of course. Then repeatedly RANDOMIZE USR 63000 for
as long as you want the effect to last. Line 1300 produces a suitable
sound effect if you've got a 128K Speccy, and 1310 turns it off again.
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