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Demos Amiga Demoscene Archive Forum / Coding / The Blitter tornado effect: How to do it ?

 

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krabob
Member
#1 - Posted: 17 Dec 2004 14:18
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Hello again all.
Hey i'm wondering how could work an oldschool effect seen in a lot of A500/A1200 demos:
I will call it the tornado effect, I thing it was done using the blitter for copying bitmap with masks.

It can be seen in "chaosland" from fairlight:



But also at the end of "fullmoon", in the dreamdealer toothbrush serie,there's a fabulous enhaced one in "arte", the fabulous "darkroom" 40kb, etc...

It must be more or less done like this:

- adding pixels as a generator in the center of the screen.
- displacing the pixels using multiple blitter masks.
- swapping a double buffer.

So my problem is: what the fuck did they used as masks ?
It is zooming and rotating, so I guess they (more or less ?)
divided the screen like a pie, in 4 or 8 pieces, and made masks with that,
and then each pass would displace all screen pixels with the (8?) masks...

Anyway, I never tried at the time i was still doing hardware codes, but I like a lot this effect (simple, intelligent), and to my mind there's a lot to do with it again.

Can some one show an image of the masks used ? Or am i totally wrong ?
Cyf
Member
#2 - Posted: 17 Dec 2004 16:22 - Edited
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take a look at the prestige cracktro (Mortal Kombat 2) by Stelios/Scoopex :
- after doublebuf, bltcon0/bltapt/bltdpt address computed, the pattern is traced with CPU in work screen. (with bset and bclr ". . . . ." set or clr x4 xNbplane something like that) and bplcon1 shift
here is the shape of pattern. (in this case, it's the same for 4 bitplanes)
- n pieces 32x48 are blitted from work screen to dest screen with computed shift and minterm for bltcon0, and new computed pos for source and dest. the mask is -1

in Darkroom, the mask is used.
now, I havent the full algo.
krabob
Member
#3 - Posted: 24 Dec 2004 10:31
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well I will build a totem for any * source * related to this effect :-)
Cyf
Member
#4 - Posted: 24 Dec 2004 16:36 - Edited
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the 7 patterns used in Chaos Land : 32x32 :
Cyf
Member
#5 - Posted: 25 Dec 2004 00:06 - Edited
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source code here (for purpose of education only)
still some bugs, but works
dalton
Member
#6 - Posted: 25 Dec 2004 00:50
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are there more where that came from?
krabob
Member
#7 - Posted: 3 Jan 2005 14:31
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yeah thanks cyf !!! really !!! i'll study that !!!
Cyf
Member
#8 - Posted: 3 Jan 2005 14:51 - Edited
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are there more where that came from?

no (I splitted the pattern 4 in 2 differents patterns, no more with 2 planes)

i'll study that !!!

please find the algo ;)

 

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