Vulgus RE progressing a little better than I initially expected!

Back from holidays (boo!) and although I haven't posted again, I've made quite a lot of progress over the last couple of weeks.

First I'll admit I haven't gone back to look at the map decoding - there was plenty to do in the rest of the disassembly that kept me occupied. Some of the aforementioned numerous variables have been identified, though there's quite a lot that I still haven't deduced, as many of them are only used in one or two places, and likely for enemy AI - they're always the most difficult!!!

Having said that, a huge portion of the code has at least been commented to a degree, if still missing some key elements of data. Aside from the map data, there appears to be a homogenous 16-byte 'object' data structure for every, well, object in the game, from the player ship, to bullets & bombs, and aliens. I've figured a few of those bytes out, and hoping I can focus on the rest now that I'm at home and have access to larger & multiple screens, notepads etc.

There's a not-insignificant amount of code for a few unobtainable self-test screens, which I've been able to see run via patching a few bytes. They threw me for a bit as I couldn't reconcile what the code was doing with what I've experienced in the game. TBH they're nothing more than a curiosity and not worth in-depth RE.

Speaking of non-insignificant amounts of code; the 'instructional' sequences showing the point scoring system is quite a chunk in its own right. I've identified the state machine responsible for the attract mode sequences and have documented parts of it, but not all of it.

Part of the instructional sequence - quite a lot of code required

My overall impression is that the code isn't exactly the best I've come across; Xevious was far neater and more efficient. There seems to be quite a bit of duplicated code, and routines called from multiple places when you wouldn't expect they would need to be. I think some of the logic is a little hap-hazard in the way it was put together. And the game actually looks a little un-finished, though those more familiar with the game probably won't be surprised to hear that. Aside from evidence in the gameplay, things like branches between different routines that are identical tend to support this theory.

And finally for this post; there's the debate over whether collection of the letters 'E', 'S' & 'D' actually help or hinder the player. I've found the code that handles this, though I haven't completed the RE so I won't say anything more just yet other than to note that initially, I thought them completely benign! That was because the code that 'collects' them doesn't actually do anything (as opposed to the code that collects the 'POW' pickups). However further analysis revealed that the code actually tallies how many you've MISSED, rather than how many you've collected!!!

My immediate focus will probably be on deducing all the elements of the 16-byte 'object' data structure - that should help identify some of the outstanding data variables. As I said, I have a few worked out thus far, and have guessed a few others, now it's time to nail them all down!