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Title Silkworm
Game Type Shoot-em-up
Players 1
Compatibility All (I think)
Submission Perks

Review
As a first time Amiga user who has acquired a 1200, together with various
software, I find the whole "Scene" rather perplexing.
So you can imagine my joy to unearth Silkworm; a blast from the past!
Now here's something I can feel at ease with (I've been here before). Back
in my youth, the distant 80's, when these games were played on Table-tops,
with a pint of Cider & Orange and a JPS in the corner of your mouth, as
your only allies. Yes this is it fast and furious, with just the one
ending ..... Blown to Buggery !
It's good to feel the adrenaline pulsing through one's body once more, with
nowhere to go, when the Game Over, pops up, you can't beat a bit of
controlled stress.. is that an Ambulance I hear?
You can keep these new adventure games, save them for the squares, and as
for the 3D stuff, I don't want my dolly-bird-mind blown just yet, thanks
all the same, in my day it was all in the wrist action.
So what's its all about Perksey, I hear you cry,
Well it's rather like that old classic Scramble, but better, as you can
choose whether you wanna be a chopper or a jeep, ripping across the
screen, or should I say," horizontally scrolling", yeh right, blasting
away, with two angles of firing lines, one stright ahead and the other
downwards. The aim, I think, is to put everything in your path TO
BED, collecting multi-shooters, temporary immunity from enemy flack by
hitting the "life mines" and gathering precious points as you travel,
searching for that next level.

Any way as I said I'm a new boy, and as yet I haven't managed to break
the hymen of the second level, though I can tell you its been a ball so
far, and as for the choice, me and my chopper will I'm sure, finally
destroy the awesome, end of level guardians and find Nirvana ....

Silkworm was one of the first games I saw on the Amiga and couldn't believe how silky smooth it was, and better than the arcade!

You really think so? Amiga Silkworm held up quite well among its contemporary Amiga games, but that says something about the state of Amiga games at the time. Arcade Silkworm on the other hand faced some really tough competition (R-Type!), and didn't do particularly well.

How long did you have to write this one?

I will have to reconstruct the sequence of events, let me think… It was my first project at The Sales Curve, and I started there in October of 1988. The Ninjas Warriors came out in 1989, and we worked on that during the summer. So Silkworm must have come out in the spring of 1989. So from October to spring… somewhere around five months or so.

Was the Amiga the lead version or were both written together?

The Amiga and Atari ST versions were written at the same time.

Silkworm features full 50 frames per second and parallax scrolling! Correct me if I'm wrong but I suspect the way you did the parallax was the main area scrolled at 1 pixel every 2 frames, the copper scrolls the game section at the bottom of the screen 1 pixel per frame, and to achieve the parallax effect you are only drawing the small hills (and any other bits that stick on top of the road) onto the screen as if they are sprites? So you only have to redraw the foreground scrolling objects every frame along with player and bullets?

You are quite right. You will notice that, as the game progresses, I need more software sprites for gameplay, and consequently the foreground scrolling objects get fewer and farther between.

The game appears to be multiplexing sprites for all the bullets, including different bullet graphics. Another guess, you put all bullets for the screen into a list, sort them by increasing y co-ordinate then x co-ordinate, and re-use the sprites in a loop?

That is correct. All hardware sprites for a frame are collected, sorted by Y (but not X) and assigned to the available sprite channels in a rotating sequence.

If that is the case, is there ever a possibility that a sprite will vanish or did you somehow make sure you'd never have more than the maximum on a scanline?

It is more than possible: it happens all the time! Especially in two player mode, with all guns powered up, and under heavy attack. But you don't notice it much, because I rotated the sprite assignments, so that every next frame, a different sprite would be dropped. The result was that when there are more than the maximum number of sprites on a line, they would only flicker, not disappear for any length of time. This is a trick that I learned while programming MSX games, which had only 4 hardware sprites.

How does the game synchronise moving the sprites around?

I'm digging around in memories from twenty years ago, so I can't guarantee accuracy. But I think this is what is going on… The sprite hardware on the Amiga has some serious limitations. If I recall correctly, to reuse a sprite channel multiple times, using the DMA hardware, the sprite position information and the bitmap must be interleaved. So the position information will be followed by the bitmap, followed by another position and another bitmap, and so on. This requires that you to create multiple copies of the bitmap in memory. Every frame, you would end up copying the sprite bitmap as many times as there are hardware sprites on the screen.

Did the various people converting each version talk to one another about how the game would work on each system or was the hardware so different that there really wasn't much in the way of code and ideas that could be shared?

The 8-bit versions were developed independently from the 16-bit versions.

Did you ever get feedback from Tecmo about your conversion? Most people seem to think the Amiga version betters the arcade!

We never had any direct contact with Tecmo. Remember that Tecmo was a Japanese company, and the Amiga was practically unknown in Japan. I imagine they didn't care much about the conversion.

It looks like you converted almost everything from the game perfectly - even the hexadecimal countdown of how many enemies before the next goosecopter! Did you consider changing that to decimal?

Of course not. We wanted to be faithful to the original.

The Atari ST version appears to run at about half the speed of the Amiga version, maybe less. Did you do any work on the Atari ST version? (It must be difficult without hardware scrolling and sprites as they were used so effectively on the Amiga!)

The Atari ST had the same CPU power, but none of the nifty blitter and copper chips that the Amiga had. All the scrolling and sprite drawing had to be done with the CPU. Full screen scrolling, in particular, is quite a heavy task for the processor. All the credit for the ST version goes to John Croudy. He made the miracle happen.

Did you ever consider adding different bosses rather than just cycling through the giant helicopter and tank? Or was the job simply to do an accurate port and not better the original by too much? :-)

We did not really have much time to add new stuff. We tried to get as close as we could to the original, and that was hard enough. And on top of that, this was my first real Amiga project - I really was learning as I was programming. I'm quite proud that we got most of the arcade game in.