
Scrolling on the Amiga - ingve
https://uridiumauthor.blogspot.com/2017/12/scrolling-on-amiga.html
======
kleiba
OMG! This is the blog of Andrew Braybrook, author of Paradroid and one of my
childhood heroes! How cool is that!

Some years back, I found his journal online from when he developed Paradroid.
I felt like being in heaven finding that treasure.

If I recall correctly, I read somewhere that he completely withdrew from the
games development scene and now works for some non-game related IT company in
the UK, but my memory on that is vague.

~~~
SyneRyder
Was that the Paradroid journal? He kept a diary for Zzap!64 magazine called
Birth Of A Paradroid:

[http://www.zzap64.co.uk/zzap3/para_birth01.html](http://www.zzap64.co.uk/zzap3/para_birth01.html)

He also wrote a diary for his Morpheus game:

[http://www.zzap64.co.uk/mentalprocre.html](http://www.zzap64.co.uk/mentalprocre.html)

~~~
pan69
Very interesting to read, but I can't seem to find a "year" when it was
written. The Mental Procrastination has a publicised issue date of 1987, but I
guess it was written before then?

Both remind me a bit of Jordan Mechner's "The Making of Prince of Persia".

~~~
SyneRyder
Probably would have been written in 1987, just a couple of months delayed.
Zzap used to publish development diaries while a game was being produced,
which meant the diaries would sometimes end midway when a game was cancelled
(thinking of the Batman Returns [1] game diary in that case).

[1] [https://www.gamesthatwerent.com/gtw64/batman-
returns/](https://www.gamesthatwerent.com/gtw64/batman-returns/)

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bitwize
The TI-99/4A had no hardware scrolling registers. Smooth horizontal scrolling
for _Parsec_ was achieved by putting the display into bitmap mode and having
the CPU manually shift the background bit patterns in a fast inner loop. This
trick (actually more like brute force) was possible because the CPU was a fast
16-bit CPU and had access to (only 256 bytes of!) fast SRAM to do the work in.
And I don't think it was able to update the character pattern tables every
frame (bitmap mode worked by having three active character pattern tables per
frame, one for each 1/3 of the screen).

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cmrdporcupine
The Sharp X68000 would outdo both the Atari ST and Amiga in this comparison.

It basically had arcade machine class video hardware. It came later to market,
but creamed the Amiga completely in specs, and they ended up shipping 25
different models of them, up to really high clock rates.

Unfortunately only really sold in Japan (though due to population size of
Japan, it actually sold a _lot_ of units and a lot of games were ported to
it).

It's really too bad it never really made it to Europe and North America

~~~
to3m
Thread about porting X68000 games to the Atari Falcon: [http://www.atari-
forum.com/viewtopic.php?t=24111](http://www.atari-
forum.com/viewtopic.php?t=24111) (bullet hell shoot-em-up video on page 19)

(Atari Falcon:
[https://en.wikipedia.org/wiki/Atari_Falcon](https://en.wikipedia.org/wiki/Atari_Falcon)
\- it's quite a lot better than the original ST, but still doesn't have
sprites or multiple playfields)

~~~
cmrdporcupine
Falcon is great. I have two ;-) And an X68000, though I'm not sure why I spent
the money to have the latter. It's a hassle to work with (5 1/4" floppies with
soft eject, hard to get parts/boards, non-standard SCSI, no decent floppy
emulators, Japanese OS, hard to get software, 15khz frame rate video output on
some games) and the PSU will self-destruct any day now given the crappy caps
in them.

------
bryanlarsen
I believe I've done smooth vertical scrolling for games on the Tandy Color
Computer, which is basically the same hardware as the Dragon 32. That was 30
years ago, so my memory is a little rusty.

I believe I used the "Can we start the screen memory on any address in video
RAM?" mechanism from the article.

There was definitely some sort of boundary limitation: IIRC I couldn't get
horizontal smooth scrolling to work, but I'm fairly sure I got vertical
scrolling working.

If anybody has an archive of the disks from T&D software they can double check
my assertion...

~~~
Someone
[http://tandd.com/software/index.html](http://tandd.com/software/index.html)
is a nice URL, but not the right one :-)

[http://www.colorcomputerarchive.com/coco/Documents/Magazines...](http://www.colorcomputerarchive.com/coco/Documents/Magazines/T&D%20Software/)
gives scans of the cassettes. I guess (but haven’t fully checked) “T&D
Software.zip” in
[http://www.colorcomputerarchive.com/coco/Disks/Magazines/](http://www.colorcomputerarchive.com/coco/Disks/Magazines/)
gives a 12 megabyte download of their contents.

~~~
bryanlarsen
Thanks a lot! I haven't found the game I'm referring to yet, but I did find
the first game I ever sold: dbreak on disk 69.

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rzzzt
See the original Uridium on the C64 in action here:
[https://youtu.be/N0TfHkNpRNs](https://youtu.be/N0TfHkNpRNs)

Smooth scrolling could be achieved in character mode by making the borders
wider, hiding 2 columns or 1 row, depending on the direction. The visible area
could then be adjusted on a pixel-by-pixel basis, revealing the hidden content
gradually.

~~~
to3m
Uridium's scrolling on the BBC Micro was also somewhat interesting:
[https://youtu.be/ToTQN6dxwDw?t=243](https://youtu.be/ToTQN6dxwDw?t=243)

Multi-way scrolling was common for BBC Micro games, as the hardware directly
supported the barrel-type scrolling described in the article, though only on a
full-screen basis. Uridium programmed the CRTC in a particular way, however,
allowing the screen's base address to be set halfway down the screen, giving a
stationary area at the top and a fixed area at the bottom.

I think the only other game of the period that did anything like this was
Firetrack
([https://www.youtube.com/watch?v=8bxdd2_qrpg](https://www.youtube.com/watch?v=8bxdd2_qrpg)),
which used it to get smooth vertical scrolling.

The technique is easy to do
([http://www.cpcwiki.eu/forum/programming/rupture/](http://www.cpcwiki.eu/forum/programming/rupture/)),
but you do have to know the trick! It's know a well-known thing, and there's a
couple of modern BBC Micro games that use it.

------
ZenoArrow
Andrew Braybrook, that's a name I haven't heard in a while. Aside from his
original games, I remember he did a highly praised port of Rainbow Islands for
the Amiga.

If you like this kind of look into old school games coding techniques, you'll
probably like GameHut:

[https://m.youtube.com/channel/UCfVFSjHQ57zyxajhhRc7i0g](https://m.youtube.com/channel/UCfVFSjHQ57zyxajhhRc7i0g)

------
Zardoz84
umm ZX Spectrum 128Kb, +2 and +3 can swap memory video banks, doing a
effective double buffering.

------
xroche
Atari ST

\- Can we start the screen memory on any address in video RAM? No, limited
boundaries. \- Can we restart the screen display from another address during
the display? No

What ? It could definitely be set to any memory address (with same 16-bit
boundary as the Amiga)

~~~
to3m
The bottom 8 bits were alway zero, so all you could really do was 8 row (1280
byte) vertical scrolling. I don’t think you could change the screen base
address mid-frame either, so you’d need a double-height buffer to do a
continuous scroll.

The STe fixed both of these problems, and had variable wid5h rows and the
pixel offset thing too. That meant a setup that was roughly equivalent to a
4-bit Amiga screen, though with interleaved bitplanes (which is not
necessarily a bad thing).

~~~
cmrdporcupine
The STe Blitter was really great, but totally underutilized because it was
such a small fraction of the ST market. Atari really dropped the ball by
getting the Blitter to market so late.

Interesting the different approaches. Commodore shipped the Amiga 1000 at too
expensive a price point, and so Tramiel (who had rushed the ST to market just
before the Amiga) got in with a rock bottom priced machine that initially
looked like it would kill the Amiga (which was his intention.) But Commodore
followed up with the cost reduced Amiga 500 which ended up winning against
Atari Corp in the home gaming market (though IMHO the ST and offshoots were
still far better productivity machines than the Amiga and did well in that
market in Germany).

Going back to some of those ST games I loved, they have really crappy frame
rates and high latencies.

