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Visdom by JAC! [web]

>>> Visdom Demo by JAC! in 1991 <<<

This was my very first real demo. The idea of the demo was to port my favorite
C64 intro (cracktro actually) by the "Hotline" crew to my machine because I
simply loved the style and the "smooth criminal" tune. Since I never was into
composing sounds and didn't know much about creating sounds I had a problem.
But there was an Atari Basic listing for a tune named "Honkey Tonkey" in some
printed computer magazine that I bought in the super market and so I ported
the replayer and the DATA statements into assembler. Maybe one day I'll find
out the original author and send him some regards. See the Atari version versus
the C64 version below.
  
The second part of the "Visdom I" demo was the result of a "coding battle".
I already had an Amiga 500 at that time and some friends of mine, who also were
coders, had started to create demos on that machine. So the group "Visdom"
was an Amiga group of 5 people and I was the "one man Atari division". We had
meetings every 3 or 4 weeks where the guys showed their progress in their
Amiga Demos and the latest stuff they had received from other groups. Well,
and I always tried to port their achievements to the Atari XL until the next
meeting. And I won this "competition" quite often and it really was fun (and
beer). One day they presented the new Megademo from the "Royal Amiga Force"
in 1989. I was amazed by the demo and immediately tried to port is to my Atari.
And since most of the other guys came from C64, they were stunned by the large
waving logo and any distortion effects with more than 4*8 pixels. So I decided
to create a demo that could not be done an C64 and looked like this part of
the RAF demo. The first version actually had an "RAF" logo, but I changed it
(since R.A.F. is the short form of a former German terrorist group ...) as
soon as I had designed my own logo in DPaint.
  
The final version was done for our on meeting 04-05-91. Because I didn't have
any other Atari contacts at that time I decided to send that version including
a small note intro to the "Disk Line" disk magazine from PPP (Power per Post)
but I don't remember that I ever got any feedback.

Despite of this, people from all over the world contacted my years later
because they had somehow received that demo. That was really funny to me.
Some weeks ago I came across an article by Heaven the the ABBUC Magazin 46
where he wrote about coding scrollers in the demo corner. There he mentioned
the "Visdom" demo for having a graphics 0 scroll with single pixel resolution
and that this probably is an example of heavy bit shifting. To be honest,
this single pixel scroll takes no more additional cycles for the single pixel
effect. Every 8 pixels, the screen memory is shifted. Every 2 pixels the
HSCROLL position is changed and for the single pixel resolution, I exploited
that every 8x8 charset is actually a 7x7 or 7x8 charset, at least for all
normal characters like letters or digits. Otherwise adjacent characters would
stick to each other. So the initialization simply creates a second charset
which is shifted 1 bit to the right and this charset is used for the odd
pixel positions. Resulting in about 10 additional cycles for this in the DLI. 

Meanwhile I also found some minor bugs in the demo and its successor.
To be honest all bugs amount to the same root cause: I only had a quite bad
color TV set at that time, so some flaws were simple not visible. But todays
emulators and screens are merciless in this regard and I don't want to be
blamed for a dutch color scheme after all these years ;-) 

This archive contains the fixed version which also runs properly on NTSC
with correct colors and allows any key to proceed to the second part.

JAC! 2012-03-13
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