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makedemo.doc
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1993-06-24
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HOW (NOT) TO GO ABOUT WRITING A DEMO
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If you are in the mood for making a demo, just follow these steps,
and...you will probably fail badly. Nevertheless, here they are:
Ask yourself, "is my demo going to be centred around a certain
subject?". In my 'law' there are these different types of demo:
i) One certain 'theme', eg. the whole demo is based around the stone
age. The scrolltext may be made up of bones, the doc-balls may be
boulders or rocks, there may be a giant animated dinosaur, etc.
ii) The demo mostly contains one new idea. For instance, if you had an
original idea (not likely) such as a three-dimensional sine distorter,
which not only goes up and down, and left and right, but in and out as
well, you would centre the whole demo around this, and probably throw
in a scroller and VU's as normal.
iii) The demo is made up of seperate parts. It may have a giant
scroller screen, then an infinite bobs screen, then, erm, a hardware-
scrolling screen, and so on.
iv) The demo is likely to consist of any old stuff chucked in as usual
by way of scrolltexts, distorters, VU's, no-borders, rasters, and so
forth.
Once you have decided what type of demo you want to do, you set about
doing the basic graphics for it (or most likely, hacking them!). If you
have come up with a new idea (such as the 3D-distorter) then do a brief
program of this first to make sure you can get it to work (it's no good
spending hours on a demo if the main part doesn't work!)
Next, create the 'shell' of the demo. When I mean shell, I mean the
basic 'logic=back', 'if hardkey=57 then end', 'screenswap:wait vbl'
type of things. I have a small program which I merge in at the
beginning of writing a demo, which has a part for initialisation, a
part for the main loop, a part for each routine, and a part for the
scrolltext messages or whatever. If your demos are logically set out,
they are easier to code and debug.
Make sure that you have a "DOKE $FF8240,$777 : DOKE $FF8240,0" just
before the "WAIT VBL". Use this to ensure you stay at 50 Hz, and delete
when you have finished.
Then, bit by bit, add each part of your screen into the main code. If
you are basing your demo on one item (3D-distorter) then do this first,
and see how much processor time you have left for the rest.
In any case, make sure you do your scroller (or message-displayer) near
the beginning, because you want this to be as smooth as possible.
Make sure that you are using the most optimized method of code, ie. the
FASTEST. Replace old or dodgy bits of code with newer ones. Replace
SCREEN COPY with SKOPY 4, or BLIT (Missing-link!) or whatever.
Once your code is finished, draw, or hack, the final graphics, and
compress them with the PICTURE COMPACTER.
LEAVE YOUR MUSIC UNTIL THE VERY END! If you have a section which
refuses to work, you get so p*ssed off with hearing the same music over
and over and over and over and over again, you lose the actual 'appeal'
of the demo. (what?)
SAVE YOUR CODE BEFORE YOU USE MACHINE-CODE ROUTINES, OR BEFORE YOUR
FIRST TRY. (There's not much worse than sitting waiting for a demo to
work, and realising that CONTROL-C doesn't do anything!)
MENTION 'BLACK EAGLE' IN THE GREETINGS LIST. (NB: NOT PUTTING IN A
GREETINGS LIST AT ALL IS A BETTER IDEA!)
There. If you have followed these steps correctly, you will probably
end up with something that looks like a cross between a set of traffic
lights, and a roll of green kitchen foil (what?) Still, I bet you
enjoyed it (actually, I wouldn't bet too much on that, come to think of
it...Then again, I will withdraw that bet forthwith.)
Article: BLACK EAGLE 24/6/93