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Old 05 August 2012, 16:18   #1
Dunny
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Need explanation of a demo effect - screen zoom/rotate

Hi all -

There were a few demos back in the day that used this effect. It appeared to be random, and a 50% dither was employed. The screen would rotate and gradually expand, creating swirls of colour as it did.

I kind of got the idea that it was rotating the screen and pasting it back in a feedback loop, but I'm not so sure.

Anyone know how it was done? I can't recall any of the actual demos that did this, but one that sticks in my mind used pink and a kind of light green colour for the effect.

Thanks,

D.
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Old 05 August 2012, 17:36   #2
Galahad/FLT
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Are we talking the blitter tornado effect as seen in Stardust and the following Prestige cracktro?

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Old 05 August 2012, 22:15   #3
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I have wondered for years how this was done. Amazing effect. Used to stare at that Prestige cracktro for ages...
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Old 05 August 2012, 22:35   #4
pmc
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Never made one but I know roughly how it's done:

Push random pixels into the centre of the display (watch the effect and look closely at the centre of the screen, you'll see it)

Blitter copy the bitmap data around and out from the centre to the edges.

The random pixels coupled with the way the blitter copies are done gives the "fractal" looking spirals.
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Old 06 August 2012, 01:49   #5
Dunny
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Quote:
Originally Posted by Galahad/FLT View Post
Are we talking the blitter tornado effect as seen in Stardust and the following Prestige cracktro?

[ Show youtube player ]
That's the one!

Quote:
Originally Posted by pmc View Post
Never made one but I know roughly how it's done:

Push random pixels into the centre of the display (watch the effect and look closely at the centre of the screen, you'll see it)

Blitter copy the bitmap data around and out from the centre to the edges.

The random pixels coupled with the way the blitter copies are done gives the "fractal" looking spirals.
Indeed. I experimented with a simple zoom instead of the blitter copy, and it didn't look good. I'd love to know how the copy is actually performed.

D.
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Old 06 August 2012, 07:59   #6
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Ah, but to know that is to take away the magic.

Experiment with various ways of copying and see what happens. My guess would be that was exactly what the original coder of the effect did.

Original is in the 40kb intro Bananamen by Stellar if I remember rightly.
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Old 06 August 2012, 08:25   #7
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Quote:
Originally Posted by pmc View Post
Original is in the 40kb intro Bananamen by Stellar if I remember rightly.
That's the first good looking feedback effect of this kind coded by Dweezil and most known. The original effect was coded by Tizzy and appeared in Shining's 40k intro released at TP'92.
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Old 06 August 2012, 09:04   #8
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OK, nice one Stinger

I'll have to check that one.
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