What is "sync scrolling"?

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What is "sync scrolling"?

Postby Total Eclipse » Fri Aug 13, 2004 9:08 am

Can anyone explain to me exactly what sync scrolling is? I know it's been used in countless demos, and some games (mainly Thalion games from demo coders I expect).

I know that TCB are considered some of the first coders to really put it to some use, and that it's meant to be able to scroll entire screens in a handful of scanlines, but I can't seem to find any more information than that!
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Postby Marcer » Fri Aug 13, 2004 10:08 am

Sync Scrolling = hardware scroll

reason for the name "sync scrolling" coz the guys from Sync said they invented this kind of scrolling 1st on atari.

But if they were first with this kind of scroll can we talk alot of. since.. some say TCB was first with hardscroll on Atari.

And as you might know.. there is not so big deal with hardscrolls nowdays. since even STe have in built in.. no cpu time when you do this..

it was harder to code this on ST..

one screen you should check out for a good example of an Hardscroll(sync scroll).. is Grodan kvack kvack demo screen by TCB. you will find it in So Watt Demo.

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Postby leonard » Fri Aug 13, 2004 1:07 pm

Well, I'm not sure where comes the name "sync-scrolling" but to me, that's related to the demo crew "Sync". to me ( maybe i'm wrong), it comes from "Synchro" scrolling, because that method use perfect synchro with electron beam ( same as fullscreen technic).
"Harware-Scroller" is the other name of that technic, simply because at the end, that technic "emulate" the hardware low byte screen adress ( register $ff820d of STE machine).
Hardscroll is quite easy to enderstand when you have invented the "fullscreen". Fullscreen use perfect "synced" routine to open borders of line. Using that method you can produce rasterline of length 230 bytes (more in real life but just note this for the moment). A normal line is 160bytes on atari. Now what append if you set the first line to 230 bytes and the 199 other at 160 bytes ? The screen appairs shifted 70 bytes to the left. ( 230-160). If you combine several fullscreen lines, you can get all combinations to emulate the low adresse registers. Of course you don't have the correct bitmap display on these 230 width lines, so simply keep the colors black during that period.
The TCB Groddan screen in Sowat demo removes the top border, but keep the lines black, so you think it's a classic 320*200 screen but in reality this is a 320*234 screen high.
In real life, you have many differents lines such as 204,158,54,80 etc.. Combin ing these lines you can do an hardscroller or 6 lines only. ( hey ULM had a 5 lines hardscroller just because they used the first synchro line :-))
hope you had answer to your question !
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Postby leonard » Fri Aug 13, 2004 1:08 pm

oh god what a lamer.... In my previous post, of course read:

"to me that's NOT related to the demo crew "Sync"" :P
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Postby Total Eclipse » Fri Aug 13, 2004 2:08 pm

Right, I think I understand that.

I remember that although the intro to Enchanted Lands appeared to scroll the entire screen, the game itself used a horizontal flip/scroll. Is this because hard scrolling requires careful timing and wouldn't leave enough CPU time for the actual game mechanics?

If not, would a plain STfm be able to run a Shadow Of The Beast 2-type game, with 8 way scrolling?

That's one of the games that really caught my attention on the Amiga (my friend had a copy), and I was quite looking forward to the ST conversion. After seeing something like the Cuddly Demos, with fullscreens and smooth scrolling, SOTB2 on the ST was such a disappointment. I know that demos use a lot of techniques to give the impression a lot more is happening than should be possible, so although something like (for example) the Cuddly main menu has a smooth scrolling screen with a parallax background, could that be used as the basis for a full game?
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Postby leonard » Sun Aug 15, 2004 9:04 am

Hum; Enchanted Lands is not Rick Dangerous ! It has PERFECT multi-directional scrolling, in 1 frame. ( that's the ONLY ST game featuring a multidirectional hardscroller). The horizontal scroll speed is 4 pixels, which make things a bit harder.

For SOTB, the ATARI SyncScrolling only emulates low byte of screen adress. That is, the best thing you can do with that is a vertical scroll of 1 pixel, but an horizontal scroll of 16 pixels ! For less pixel scroller ( say 4 ), you have to trick a lot (using many memory). That's why Enchanted Lands is very technic: it runs on 512Kb machine and uses many screens. To keep some memory, sprites are displayed on the showed screen. To avoid flickering, sprites are draw, sorted to the electron beam. What a mess ! :-)

And the last feature an ATARI can't do is multi-plane scrolling using sync-scrolling. Syncscrolling scrolls the whole screen (4 bitplanes). (on the AMIGA you can scroll the bitplan you want). The parallax scroller is cuddly menu, or in Darkside of the spoon, or in my nostalgic-o-demo uses the same trick: look at the second layer of these demos: it always a 8 pixel width bitmap !!! ( that's related to the horizontal speed scroller of 4 pixels). So you can't have a large bitmap for a parallax ( and 8 pixels bitmap is a bit short for a game :-))

So, even on STE where the 1 pixel speed scrolling is possible because of the hardware, I don't think you can do a SOTB like on ATARI. Anyway, the "best" SOTB-like screen in the intro of Enchanted Lands, featuring multi parallax, large bitmaps, colors etc. That screen is *full* of tricks and uses 100% of CPU. You can't add other game stuff. There is a "big SOTB graphics" screen too in "Vodka Demo" by Equinox, but features less parallax scroller.
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Postby Gunstick » Thu Aug 19, 2004 6:43 pm

leonard wrote:hey ULM had a 5 lines hardscroller just because they used the first synchro line :-)


Sencond half of the first line to be extremely precise.
Noone else did that? Would be surprising to me.

Georges

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Postby bodkinz » Thu Aug 19, 2004 7:01 pm

personally i thought ULM did some of the best fullscreens... Dark Side Of The Spoon was one of the best Megademos i've seen... the fullscreen scroller with distorting background is one of my all-time favorites.. I still load that demo/screen up from time to time.. nice sample too.. makes the hairs on the back of my neck stand on end and gives me goose pimples...

nice one

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Postby Gunstick » Thu Aug 19, 2004 9:45 pm

bodkinz wrote:personally i thought ULM did some of the best fullscreens... Dark Side Of The Spoon was one of the best Megademos i've seen... the fullscreen scroller with distorting background is one of my all-time favorites.. I still load that demo/screen up from time to time.. nice sample too.. makes the hairs on the back of my neck stand on end and gives me goose pimples...

Bodkinz


Hmm, I should do an MP3 of the full song. It's "You" from Boytronic. I actually bought the LP (in a cheap sale) just to get the song I recorded from radio so I got something good quality in the demo.

Maybe someone can find the MP3... so I don't need to digitize it (it's on vinyl, and I don't have a player anymore).

Georges

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Postby bodkinz » Fri Aug 20, 2004 10:50 pm

Oh by the way i have a fully cracked copy of Dark Side Of The Spoon..

I knew a person that used to crack any megademo i wanted... he cracked the cuddly demos as well.. but i'm not sure i have that disk anymore :lol:

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Postby Gunstick » Sat Aug 21, 2004 2:09 pm

bodkinz wrote:Oh by the way i have a fully cracked copy of Dark Side Of The Spoon.


Whahahaahaaa :lol: :lol: :lol:

I have the full source code of DSOTS :wink:

Georges

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Postby ggn » Sat Aug 28, 2004 12:20 pm

Gunstick,

I also have a couple of sources too (Main menu and another one I don't remember now :)), found on various ftp sites. Haven't had the stomach to look at them yet though ;)

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Postby Gunstick » Sat Aug 28, 2004 4:10 pm

The sources are a bit non-explaining, so anyone will have quite a headache to figure out what's going on.

If I ever find the time, I will expand the DSOTS website with techincal explanations, how all this works.
time... hmm, now that's a problem!

Georges

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Postby ggn » Sat Aug 28, 2004 10:21 pm

Well, that would be fun :) Of course, demystifying some tricks takes a lot of that mythical status ("how the f..k does he do it???") one creates in his mind for some screens!

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Postby Gunstick » Sun Aug 29, 2004 12:33 am

I quote from the scroller of the parallax distorter:
do you want to know how i manage to shift all the scrollings??? well
the dma chip can serialize data. by programming it in a special way
(reading and writing the same time)
the dma sends the data back, but shifted by one bit

well ok, not really.
Those who believe that, don't understand how the ST works :-)

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Postby ggn » Sun Aug 29, 2004 12:32 pm

Well, I claim to be stupid on occasions, but not that much :)

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Postby leonard » Thu Sep 02, 2004 7:35 am

bodkinz wrote:personally i thought ULM did some of the best fullscreens...


Have to admit the paralax distorter is one of my favorite screen on ST. If you ask to do the same to an AMIGA programmer he has to really think about it.
That screen has all: 1 VBL, fullscreen, hypnotic sample sound, amazing large moving area.
Older but one of my fave fullscreen is the famous "Fullscreen" of cuddly demos ! 4 pixels multi-scrolltext, oldskool at its best ! :-)
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Postby ggn » Thu Sep 02, 2004 12:39 pm

Both quite brilliant fullscreens you mention there, although your spinning cube in fullscreen wasn't bad as well :)

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Postby simonsunnyboy » Thu Sep 02, 2004 5:24 pm

Gunstick wrote:I quote from the scroller of the parallax distorter:
do you want to know how i manage to shift all the scrollings??? well
the dma chip can serialize data. by programming it in a special way
(reading and writing the same time)
the dma sends the data back, but shifted by one bit

well ok, not really.
Those who believe that, don't understand how the ST works :-)


Already guessed that this was a joke. But actually I'm wondering what the real trick is about...more of this perverse 50/60Hz switching?

I must admit the mentioned screen is not my favourite as the scroller is hard to read for me ;)
I prefer the playfield menu in DSOTS :D
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Postby bodkinz » Thu Sep 02, 2004 6:16 pm

well personally all i thought that could be used wasd the keyboard processor.. but what do i know? not a lot :)

however you managed it you did well gunstick :) :)

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Postby TME » Sat Sep 04, 2004 11:20 am

"You" from BOYTRONIC is now available on http://www.frosties.org/you.mp3. Enjoy !

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Postby leonard » Sun Sep 05, 2004 6:28 pm

Just listen the "You.mp3" tune ! Fantastic ! Sounds really poor, english accent is so bad maybe the singer is french ! :-)

Very oldskool electronic music, sometimes looks like "Alphaville" :-)

I definitivly prefer the short sample of the paralax distorter !
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Postby Gunstick » Sat Sep 18, 2004 4:25 pm

leonard wrote:Just listen the "You.mp3" tune ! Fantastic ! Sounds really poor, english accent is so bad maybe the singer is french ! :-)


Whaaa!!!!!!!!!!!!!!!!!!!!!

Nostaligca!!!!!!!

I think I'm the only one in the world who has listenend to that song about 1000 times.
First to sample it, then in the demo. For months!

I was a quite dissapointed by the LP, it's all crap and even this song was different on LP than the one I recorded from radio. So as far as I remember I finally took the radio sample anyway.
The sample on the DSOTS website is from the original sampled data I did in 1990.

More infos about that fullscreen. Development time took about 5 months. There have been 45 different source code versions. The source code is about 160K long. Biggest problem is memory, so the soundsample is realtime decompressed during playing and the font is realtime shifted. The height of the font used was determined by the available cpu time (write the screen, when finished, "order" a font of that exact size).

And there have been other samples in pre-versions before finally using the one from Boytronic.

The oldest I could find is the pre-pre-test screen to check the possibility to make this actually work.
Get it here: http://www.cpu.lu/~gkes/ulm/2DIST012.PRG
Instructions: keypad 2/8 is HWscroll up&down. 5=stop HWscroll
Push 20 times on 8 to get a lamer's fullscreen distorter. But don't run it too long as it will overwrite all memory and you get a nice crash.

Georges

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Postby leonard » Wed Sep 22, 2004 11:49 am

Very interesting historical comments ( I like demo history :-))

Well your "sample packing" is interesting, I just look at the code using SainT debbugger. Seems to be a "4bit delta" like coding. Could you explain more about it ? An 8bits value is used for two samples, but the bit 0 is cleared, so 7 bits are used for twso samples. Is the table computed to get a 3.5bits delta per sample, or is there another trick ?

Btw, I just see using the SainT cycle counter the digisound seems to be played at 7.8Khz. I always though the digit of paralax distorter was 15khz...

Arnaud
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Postby Gunstick » Wed Sep 22, 2004 7:14 pm

leonard wrote:Very interesting historical comments ( I like demo history :-))

Well your "sample packing" is interesting, I just look at the code using SainT debbugger. Seems to be a "4bit delta" like coding. Could you explain more about it ? An 8bits value is used for two samples, but the bit 0 is cleared, so 7 bits are used for twso samples. Is the table computed to get a 3.5bits delta per sample, or is there another trick ?


it's the famous (or not) high quality delta sound packer. The sample differences are encoded on 4 bits. The low bit is not cleared (at least I hope). There are 16 different delta values, each is double of the previous one (1, 2, 4, 8, 16...)
The high quality trick is that the encoder does not check for overflow (going over 255) but explicitly uses this. So to go from 250 to 4, I don't use -128 but +8 which gives the value 2, a lot closer to 4 than 122 obtained by the classic method.

"But you need 8 positive deltas, and 8 negative and zero, that makes 17 not 16"

Well, it just happens that choosing two's potenzes makes the biggest delta 128, and that is the same as -128 if you are calculating with 8 bit values. Tadaaaa! ULM rulez :)

Btw, I just see using the SainT cycle counter the digisound seems to be played at 7.8Khz. I always though the digit of paralax distorter was 15khz...

Arnaud


7.8 or 7.5 yes, and if you check closer, every second scan line where there is no digit it's not just filled with NOPs but there the font shifter is busy shifting grafics. All interleaved and optimized by hand.

There is also a digisound / bounce synchronizer because that was easier than to get the code and sample AND bouncewave exactly right.

And there is... and also... and...
I think the secret of the ULM screens is that in every screen we used almost all techniques we know. Unused NOPs were prohibited!

Georges


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