05 August 2012, 16:18 | #1 |
Registered User
Join Date: Aug 2006
Location: Scunthorpe/United Kingdom
Posts: 1,982
|
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. |
05 August 2012, 17:36 | #2 |
Going nowhere
Join Date: Oct 2001
Location: United Kingdom
Age: 50
Posts: 8,988
|
Are we talking the blitter tornado effect as seen in Stardust and the following Prestige cracktro?
[ Show youtube player ] |
05 August 2012, 22:15 | #3 |
Registered User
Join Date: Feb 2008
Location: warrington UK
Posts: 118
|
I have wondered for years how this was done. Amazing effect. Used to stare at that Prestige cracktro for ages...
|
05 August 2012, 22:35 | #4 |
gone
Join Date: Apr 2007
Location: completely gone
Posts: 1,596
|
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. |
06 August 2012, 01:49 | #5 | ||
Registered User
Join Date: Aug 2006
Location: Scunthorpe/United Kingdom
Posts: 1,982
|
Quote:
Quote:
D. |
||
06 August 2012, 07:59 | #6 |
gone
Join Date: Apr 2007
Location: completely gone
Posts: 1,596
|
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. |
06 August 2012, 08:25 | #7 | |
move.l #$c0ff33,throat
Join Date: Dec 2005
Location: Berlin/Joymoney
Posts: 6,863
|
Quote:
|
|
06 August 2012, 09:04 | #8 |
gone
Join Date: Apr 2007
Location: completely gone
Posts: 1,596
|
OK, nice one Stinger
I'll have to check that one. |
21 April 2023, 12:37 | #9 |
Thalion Webshrine
Join Date: Jan 2004
Location: Oxford
Posts: 14,344
|
Bumping a very old thread
I liked this effect. There was an intro/cracktro (crystal/melon/lemon.?) with this effect (and the music by Radix Paul The Penguin) Unlike the others it appeared to be more than 1bpl (i.e. it was in colour) but I can't find it |
21 April 2023, 13:10 | #10 |
ex. demoscener "Bigmama"
Join Date: Jun 2012
Location: Fyn / Denmark
Posts: 1,624
|
The Bananamen one is multicolor, but haven't looked closely enough to determine if they just repurpose an older frame for the other bitplane..
|
21 April 2023, 13:24 | #11 |
Defendit numerus
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 53
Posts: 4,468
|
This?
|
21 April 2023, 13:36 | #12 |
Thalion Webshrine
Join Date: Jan 2004
Location: Oxford
Posts: 14,344
|
Yes like that. I still can't find the exact intro I was looking for.
|
21 April 2023, 13:42 | #13 |
Defendit numerus
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 53
Posts: 4,468
|
|
21 April 2023, 14:11 | #14 |
Registered User
Join Date: Jun 2016
Location: europe
Posts: 1,039
|
2+ bpls is simple: interleaved bitmap, blit height x2+, random pixels in the middle have random colors.
Full Moon (aga) by VD/Fairlight, which kind of matches that gif's palette, has 4 bpls but it's prerendered animation. |
21 April 2023, 14:44 | #15 | |
Defendit numerus
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 53
Posts: 4,468
|
Quote:
The thing about my colors version is that I pretty much randomly picked a couple, liked them and left it here But.. what do you mean by "prerendered animation"? |
|
21 April 2023, 14:48 | #16 |
Thalion Webshrine
Join Date: Jan 2004
Location: Oxford
Posts: 14,344
|
I had noticed it repeats on a very short loop unlike others I've seen. But the "animation" is quite long 1s / 25 frames?
Last edited by alexh; 21 April 2023 at 14:54. |
21 April 2023, 14:56 | #17 | |
Defendit numerus
Join Date: Mar 2017
Location: Crossing the Rubicon
Age: 53
Posts: 4,468
|
Quote:
(what you see from my gif is a grab from winuae, for a 2 bitplanes version and it can work on base A500) EDIT: I will use it shortly in a little intro; it's nothing new, but nice to look at Last edited by ross; 21 April 2023 at 15:03. |
|
21 April 2023, 15:09 | #18 |
Registered User
Join Date: Jun 2016
Location: europe
Posts: 1,039
|
If you look in memory you'll see a whole lot of prerendered screens with that fx (it generates the animation at the start of the end-part and then plays it in a loop). "Only" the zoom scroller is realtime. I don't have the exact numbers, but let say fullscreen is 10kb *4bpl *25 = 1mb. No problem for A1200.
You can also add a watch at $dff058 in winuae and you'll see it only does 1 word wide blits (other than blit clear), tornado is typically 3 words (2 and +1 for shift) wide. |
21 April 2023, 15:13 | #19 |
Registered User
Join Date: Jun 2016
Location: europe
Posts: 1,039
|
|
21 April 2023, 18:12 | #20 |
Registered User
Join Date: Aug 2006
Location: Scunthorpe/United Kingdom
Posts: 1,982
|
Oh man it's been a minute. I managed to get this coded up - here's my BASIC interpreter running the effect in 800x480, 256 colours:
[ Show youtube player ] |
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | |
Thread Tools | |
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Metropolice Demo screen resolution problems | mfletcher | support.Demos | 13 | 15 October 2021 00:21 |
Full screen 'copper' flashing Jesus On-e' Demo only after v1.6+ | prof72 | support.WinUAE | 5 | 10 August 2010 17:05 |
Error explanation?? | ORSM T | support.Hardware | 7 | 01 June 2007 07:36 |
code explanation | BippyM | Coders. General | 19 | 01 May 2007 14:12 |
Selection-screen Global Effect | Tim Janssen | support.Games | 15 | 18 October 2002 08:33 |
|
|