Atari ST games with smooth scrolling - how?

[rothers]

Originally Posted by Coagulus

I think there is confusion between push scrolling and constant scrolling. Both of these can be done in hardware or software. The giveaway on Ghosts'n'Goblins was that the score disappears while the screen scrolls. Scrolling just means a screen display moves not whether it follows a player or does it in bursts. Hardware scrolling is when this scrolling is achieved with the hardware and not by redrawing the screen in software.

Also isn't this thread about the ST?

The CPC thing comes up quite a lot. It can scroll and has various ways of doing it both push (which was used back in the day a lot) and real scrolling which was not used until the 90s for whatever reason.

[Tigerskunk]

Originally Posted by Coagulus

I think there is confusion between push scrolling and constant scrolling.

Never heard of these "categories".

Originally Posted by Coagulus

Both of these can be done in hardware or software.

This is true.

I think we are having two different discussions here.

One is about hardware registers existing that shove the screen n pixels to the left. The other seems about if that happens in one pixel steps or not.

[Galahad/FLT]

Originally Posted by Tigerskunk

Never heard of these "categories".


This is true.

I think we are having two different discussions here.

One is about hardware registers existing that shove the screen n pixels to the left. The other seems about if that happens in one pixel steps or not.

Push scrolling was more common on Atari ST. Quite often there wouldn't be constantly scrolling, it would only scroll when character got near to edge of screen, then game would halt briefly as it scrolled on the next part of the level, obviously character would be scrolled back to opposite side.

Enchanted Land did a slightly more refined version on ST which for some inexplicable reason was duplicated on Amiga.

Personally, I have no problem with push scrolling if its not a fast action game

[Bruce Abbott]

Originally Posted by Marce

the amstrad cpc was very buggy computer even the spectrum scroll 100x better than the amstrad

Only 100x, are you sure?

look at ghouls and ghost in the spectrum then look at the cpc version
the speccy version scroll is perfect is far better, idem for GNG etc

The ZX Spectrum has no hardware scrolling capability. It's only saving grace is a 256x192 1 bit per pixel bitmap, which can software scroll faster than the Amstrad because there is less data to move (6kb vs 16kb).

The Amstrad CPC has hardware scrolling via the 6845 CRTC chip. It is normally limited to 'character' scrolling, which is 8 pixels horizontally in hires (640x200), 4 pixels in medium res (320x200), and 2 pixels in lores (160x200). The scrolling distance is always the same (1 hires character width) so to make it look smooth it has to be scrolled fast. There is a way to get smaller scroll steps by adjusting the width of the horizontal sync pulse, but this only works properly with some monitors.

Many CPC games were ported from other platforms with either no hardware scrolling or incompatible hardware, so software scrolling was often used in a reduced screen area. Even worse, some Spectrum ports emulated the Spectrum's 1 bit per pixel graphics in a medium res (4 color) screen using only half the available colors, complete with color cash! This could make the CPC scroll half as fast or worse (not 100x worse though).

[roondar]

On the topic of ST games, I've seen a bunch of ST games that use smooth vertical scrolling (Paradroid 90 springs to mind). Is this what they call 'Sync Scrolling'?

I've always wondered how that works, as it doesn't seem to be a HW supported feature.

[chb]

Originally Posted by roondar

On the topic of ST games, I've seen a bunch of ST games that use smooth vertical scrolling (Paradroid 90 springs to mind). Is this what they call 'Sync Scrolling'?

I've always wondered how that works, as it doesn't seem to be a HW supported feature.

Not sure about P90, but a quite good explanation can be found here:
https://www.atari-forum.com/viewtopi...p=39325#p39325


In short, usually you can only set the STs display address in 256 byte increments, but by switching between 50 Hz and 60 Hz modes in the right places, some ddfstop-like comparisions are disabled and the graphic chip can be tricked into fetching "too much" data, thus ending up on an arbitrary (even) address. So there are some (black) lines at the start of the frame needed to prime the display.

[Tigerskunk]

I have the highest respect for the ST coders, and the shit they have to put up with...

[roondar]

Ah, that's quite interesting, thanks. Always nice to see some proper HW banging going on to utterly confuse the poor built-in chips and get the results you want

[vulture]

@DanScott

yup, 25/30

[Keops/Equinox]

Syncscroll on the ST is a demoscene thing, it was the next logical step after the fullscreen technique. Basically, it's all about managing to have different formats of lines at the beginning of the frame, instead of the regular 160 bytes per line in low res, which results in faking a new screen address, hence making the entire screen scroll.

Those tricks rely on perfect beam synchronization, with resolution and screen frequency changes at perfect timings in the frame, many times per scanline.

For the fullscreen technique, it means that any code you have has to be cycle constant and precisely integrated in your fullscreen routine each line.

The syncscroll technique was used in very few ST games made by demomakers (Enchanted Lands, Lethal Xcess, No Buddies Land, Leavin' Teramis)

Paradroid 90 did not use that technique, whatever they used was probably just regular brute force 68000 scrolling with movems.

Coding on the ST is actually very fun, it makes you work with constraints and come up with crazy ideas and techniques such as the syncscroll trick. That's probably how Leonard came up recently with the fastest mod player ever on the Amiga, he used a trick similar to what we used to play soundchip tunes on the ST in fullscreen.

[Tigerskunk]

Originally Posted by Keops/Equinox

Coding on the ST is actually very fun, it makes you work with constraints and come up with crazy ideas and techniques such as the syncscroll trick. That's probably how Leonard came up recently with the fastest mod player even on the Amiga, he used a trick similar to what we used to play soundchip tunes on the ST in fullscreen.

Like I always say, you have to see each platform on its own.
There is no bad hardware, only challenges to get something great out of it.

That said, if i were to create something for the ST, I'd probably go for a switch screen approach like Cybernoid or Exolon.

[roondar]

Originally Posted by Keops/Equinox

Syncscroll on the ST is a demoscene thing, it was the next logical step after the fullscreen technique. Basically, it's all about managing to have different formats of lines at the beginning of the frame, instead of the regular 160 bytes per line in low res, which results in faking a new screen address, hence making the entire screen scroll.

Those tricks rely on perfect beam synchronization, with resolution and screen frequency changes at perfect timings in the frame, many times per scanline.

For the fullscreen technique, it means that any code you have has to be cycle constant and precisely integrated in your fullscreen routine each line.

The syncscroll technique was used in very few ST games made by demomakers (Enchanted Lands, Lethal Xcess, No Buddies Land, Leavin' Teramis)

Paradroid 90 did not use that technique, whatever they used what probably just regular brute force 68000 scrolling with movems.

Coding on the ST is actually very fun, it makes you work with constraints and come up with crazy ideas and techniques such as the syncscroll trick. That's probably how Leonard came up recently with the fastest mod player ever on the Amiga, he used a trick similar to what we used to play soundchip tunes on the ST in fullscreen.

Thanks for the detailed explanation. Pretty cool stuff for sure. Love hearing about tricks on other platforms from time to time

[Asman]

Originally Posted by Coagulus

I think there is confusion between push scrolling and constant scrolling.

I think that I am not fully understand what is push scrolling. I think I need some game examples. Can someone post some games or youtube links. TIA.

[kremiso]

Originally Posted by Asman

I think that I am not fully understand what is push scrolling. I think I need some game examples. Can someone post some games or youtube links. TIA.

i presume something like Addams Family ST :

[ Show youtube player ]

[Tigerskunk]

Originally Posted by Asman

I think that I am not fully understand what is push scrolling. I think I need some game examples. Can someone post some games or youtube links. TIA.

It's when you are not scrolling continously, but in "batches" of a few chars at a time.

That's how I understand it, anyhow...

[Megalomaniac]

Yikes. Any push-scrolling conversion of a game designed to have smooth scrolling must instantly be much harder than the original version. Add in diagonally-scrolling blind jumps and it must become borderline unplayable (check out ST Robocod for an example). No wonder most of the best platformers on the ST were vertical scrollers or flip-screen.

[Marce]

btw,

the amstrad cpc was so buggy that even the vertical scrolling is bad
I just was testing ikari warriors , the vertical scrolling is horrible, slow and cause partial gfx corruption, the game is colorful but slow and blocky gfx

again in this case the zx spectrum version is far better, less colorful but smooth and better resolution

[Marce]

Originally Posted by Asman

I think that I am not fully understand what is push scrolling. I think I need some game examples. Can someone post some games or youtube links. TIA.

well I think you call push scrolling for ex the game addams family st version
the Amiga version of adams family performs perfect horizontal scrolling

just play both versions then u will understand

[Havie]

Originally Posted by Asman

I think that I am not fully understand what is push scrolling. I think I need some game examples. Can someone post some games or youtube links. TIA.

Push scrolling is where the screen doesn't continuously scroll, it only scrolls when you reach a certain point on the screen (the right if you are scrolling horizontally). At this point, the game the screen scrolls left the equivalent a set amount and then the game continues.

This is different from something like a beat 'em up which may not scroll until you get to a certain point on the screen and then continuously scroll or even pause to allow a certain number of fights before then continuously scrolling to the next section.

So simply - push scrolling is when the screen doesn't scroll continuously and when you get to a certain point, the screen 'pushes' you back as it scrolls a a certain amount in one go. Obviously this is less CPU intensive as scrolling is not happening every frame or loop of the code.

The Adams Family is a good example (ST first and then the Amiga is next)

[ Show youtube player ]

[SyX]

Originally Posted by Marce

btw,

the amstrad cpc was so buggy that even the vertical scrolling is bad
I just was testing ikari warriors , the vertical scrolling is horrible, slow and cause partial gfx corruption, the game is colorful but slow and blocky gfx

again in this case the zx spectrum version is far better, less colorful but smooth and better resolution

Ikari Warriors is not using hardware scroll in the cpc and you need hardware scroll for having an smooth scroll in this machine.

IW is a typical zx port using software scroll and hidden buffer. For me, the worst thing is the use of a hidden buffer instead of double buffer, wasting even more cpu in the process of drawing the screen; and of course, making visible an annoying tearing when the screen scrolls.

If you really want to understand how the cpc hardware scroll works, I will be glad of explaining to you in all detail.

And if you want to see cpc games making use of the hardware scroll, you can take a look to games as Prohibition by Infogrames or Skateball by Titus, for example. But it is very important to see those games in a CPC using a CRT, you will not feel smooth by looking them in youtube videos.