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2) How is the smooth scroll achieved in ZX-Spectrum converted games? IMHO the best ones are Commando Tracer and Desperado.

Simple, most (almost all) games do the scroll as zx spectrum do. they change only the routines needed to copy the hiiden buffer of ZX to ZX VRAM in a way that the ZX buffer is adapted, real time, during copy to vram to the different vram layout.

Here is the problem! Instead on rewrite the entire routines to achieve more speed in the different vram layout of msx they only perform the conversion when writing to vram. this result in slow speed.

Take a look, every converted game runs almost twice fps in ax than in msx. This is due to the slow convertion when writing in vram, because when doing that conversion they cannot use ldir commands as they do in ZX to copy the backbuffer to vram.
They cannot use neither otir. The vram physical corrispondence between pixels and memory addresses is too different...

Thanks, PingPong. And about scrolling like Pippols and Exoide-Z?

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Thanks, PingPong. And about scrolling like Pippols and Exoide-Z?

Exoide: not known.
Pippols. They waste a huge set of charaters. they have a charater set not scrolled, a charater set scrolled by 1 pixel down, a charater set scrolled by 2pix down and so on until reach 7. So 8 different charater sets.

During scrolling they 'print' the correct charater set...

@PingPong
actually we were discussing about scrolling in scr4 (on MSX2)
in case your original question was about msxdev competition,
I have to stress that all the methods discussed here
http://www.msx.org/forumtopic6415.html
are for msx2

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@PingPong actually we were discussing about scrolling in scr4 (on MSX2) in case your original question was about msxdev competition, I have to stress that all the methods discussed here http://www.msx.org/forumtopic6415.html are for msx2

Thx, for precisations, but my only scope was to use the 'distributed' knowledge among msx people to get an idea how what are the ways already used to overcome msx1 limits and to stretch the old msx1 to its limits.

So, if anyone know more games that have interesting work around on those scrolling limitations i will be interested to learn of . (But please no speccy convertions, they are on different hw, thus they do not stretch msx to its limits)
Actually i consider best the GROG's REVENGE/Moon patrol do you know? If no, get those from anywhere, and watch.

A floating idea:
In SCREEN 1 we can store up tp 8 tilesets in VRAM

Let's say that :
one tileset position is spent for sprite definition
one tileset position is for PNT (768bytes) + SAT (128bytes) + tiles colors (32bytes)

This imply that in screen1 you can have 6 tilesets

I think that 4 of them could be sufficient for a smooth horizontal scrolling

while 2 of them could be used for extra sprites or for extra tiles

Does anyone know if Theseus or any other game used this tecnique (multiple tilesets stored in VRAM) ?

Unfortunately scr1 offers limited color support, but in scr2 you cannot have multiple tilesets even when the room in vram is available

I don't remember how smooth Bosconian was exactly, but I'm surprised nobody here has mentioned Pitfall II yet. It also had quite a smooth vertical scroll.

Yes! the pitfall series!

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A floating idea: In SCREEN 1 we can store up tp 8 tilesets in VRAM

IIRC, the same addressing restrictions from sc2 also apply to sc1. So while you can store them, you can't activate them without copying.

No, in scr1 you should have complete use of the registers
and the tables can be moved by steps of 2K

Look at the VDP manual, AFAI can see there is no restriction

What kind of strange beast is the VDP if restrict the granularity of the addressing based on the display mode?

A cheap chip
:-)

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A cheap chip :-)

Sometimes i would like to know the vdp engineers to shake them the hands...

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Avenger is quite smooth as well, iirc, also from Gremlin Graphics. And of couse Bosconian, but you can hardly call that a scroll, as it's just sprites moving.

same with Hype, I guess? That game is really smooth, but the background's just a bunch of stars....

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Sometimes i would like to know the vdp engineers to shake them the hands...

We gotta love these old systems for what they are, flaws and everything. If we hate something about the machine we program for so much, maybe that means we shouldn't be doing it! =)

I think of little details that could be different all the time (with the VDP in the MSX1 and the PPU in the NES, mostly - in fact, if those 2 were combined it could be great!), but in the end there is no way, we gotta like'em for what they are.