(GG) Sonic 2 Auto Demo Prototype (1991-12-05) - Info & Download

OK, a few more notes, this time via savestates:

00B8 - 38B8 appears to be VRAM of some rights (it's where the art is, let's put it that way.
38B8 - 3FB7 is possibly chunks/blocks data for arranging the art (Might simply be plane mappings in VRAM thought VRAM 00B8 - 40B7?)
40BC - 50BC (approx) is definately layout data.

When I get back from work later tonight, I'll start writing some sort of extraction tool to read the savestate data, and dump out full bitmap images of the levels. Just so we have full clear maps of the levels.

 

Nice to see this finally in our hands, thank you everyone involved!

 

Collecting 99 rings doesn't seem to give you an extra life - it just resets the counter. Likewise there are no time overs.

 

This is all pretty exciting stuff, looking forward to seeing what other treasures surface.

Keep up the great work!

 

You can also crash (or reset in this case) the game by holding right OR holding left at the start (see the effects quicker by using a fast forward feature).

I would imagine it's something to do with Sonic going off-screen at the bottom, but the way he gets there is super bizarre. Holding left for example - Sonic runs off to the left and appears on the right a few times, but he also seems to go up imaginary hills and get stuck in imaginary walls, as if he's colliding with a level layout that isn't there. If it was a garbled mess of collision data you'd expect more erratic behaviour.

 

Bahahahaha, try going backwards through the loop in Green Hills Act 1. That probably explains why they were made to be one-way in the final game!

 

Heh. Push to youtube worked. So anyway, again, did a stream last night and we basically covered every level a few times in this. Its a bit long and messy. No commentary, but conversations in the IRC chat explain everything including which zone we're on etc etc



EDIT: Ugh. Sorry for the quality. Didn't stream it in 720p so... :/ EDIT 2: huh... nvm youtube seems to have caught up with its. 720p is a go.

 

Isn't his object warping to the other side of the map?

Also, they ended up fixing that crashing bug when Sonic falls through the bottom of the level by... filling every single hole with spikes. Makes you think.


EDIT: Hey, the skidding animation is less buggy here than in the final.

 

I quickly disassembled the sound driver. It doesn't look very different from the one used in the final version of Sonic 2 SMS (I haven't disassembled S2 GG yet), except for one additional routine that seems to load SFX.
There is only 1 song and the sound bank is pretty empty in general. Some of the PSG envelopes are different from the final. (btw: The song uses 03, 06 and 08, envelope 03 is different from Sonic 2 SMS/GG final.)
One thing is interesting: In Sonic 2 final, SFX start at ID 9A. In the demo, they start at 90. I assume they didn't have any songs finished yet.

You can download the disassemblies of the GG Demo and the SMS final here. (plain ASM files for now)

 

I dissassembled it too, there are only approximately 3 changes in total. I tried porting it to Sonic 2 SMS final, and here's what I got. It's compilable, but not working because I may have messed up some array pointers:
http://share.cherrytree.at/showfile-16410/sound_driver.asm

 

This is really neat. Found a couple of weird things.

First off, you can just walk through walls. No special trick, just keep walking in the direction of the wall until you break free to the other side of the collision. Useful for walking through GHZ2 and 3, for instance.

Secondly, the game irrecoverably crashes if you go above or below the level boundaries. Not sure if that's been mentioned yet. There's a couple exceptions though. In Sky High Act 2 (or whichever one is just a rainy background and a cliff), you don't crash. It just kind of wraps around. Maybe the crash has something to do with the (obviously) buggy collision engine?

In UGZ 1, there is lava at the very bottom of the level. It takes effort to get into, but it is there. The game behaves very erratically when you jump in it. Usually it just crashes. Other times, however, the screen turns blue and Sonic keeps falling until he decides to find land. Attempting to move at this point crahses. Once I even got it into a state where it looked crashed, but wiggling the joypad around caused to enter the blue void, followed by an immediate crash due to the fact that moving in the blue void crashes the game. I'm assuming this is because the game loads garbage data from RAM when out of bounds which causes the game to jump somewhere it shouldn't (badly programmed case-switch? Just guessing; wouldn't know where to start looking for that.) and executes random crap. Quite weird.

Screenshots of the blue void:

Spoiler

 

I noticed that in the early version of the much-maligned GHZ Act 3, the act ends with the area shown in that (likely) mockup screenshot showing Sonic fighting the GMZ boss with Robotnik flying overhead. (Of course, no boss here, just invislble loops for Sonic to run around!) There's also a S-tunnel right before it.

 

So far from what I've seen I think that originally there were going to be many more gimmicks in the game, the S-Tunnels being in many of the levels in this Autodemo. And from that video that Tanks posted I noticed that there was an area in UGZ that looks like it was going to either push in and out like a crusher or it was going to be a door that you had to find a switch for. Nothing really that new but I found it quite interesting, and I didn't really see anyone point that out.

Spoiler

EDIT: Re-uploaded the picture to be smaller, I don't know what I was thinking with that size!

 

I've just realised aspect build the engine from the ground up, for some reason I'd always assumed they would have inherited it from ancient.

I can't get over how quickly this was explored, I suppose tools, skills and understanding have come a long way since the Wai proto.

 

I've started work on a split disassembly. The repository is here here. I plan to spend most of the weekend on it.

 

I want to have a go at tidying these layouts up and forward porting them to the final build (Sonic 2 delta 8-bit =P). Those S bends could be adapted to the scrambled egg pipe "collisions" easy enough. I'm just too busy at the moment to sit down and get stuck in. Someone else will probably beat me to it.

 

Maps. If people would make maps we could add them to the wiki.

 

Did I not hear mention of a functional boss?

 

I was confused by that as well. I believe they meant a semi-complete GHZ boss level. I don't believe there's any data for badniks or bosses of any kind in the autodemo... :/

 

After playing round with this a bit last night I'd say there's barely a functional Sonic in there - I'd be surprised if there's any enemy/boss data as a result.

Very interesting that this build seems to pre-date some of the early Sky High pictures from magazines. From looking at magazines, it looks like the Zone was adapted to use the larger checkered floors that Green Hills Zone uses in the AutoDemo, then was updated again to match Green Hills when it changed to its' final Emerald-Hill-esque look. Which makes me wonder - is it possible the smaller checkers we see on Sky High in the AutoDemo are remnants of an older look for both zones, and that only the Green Hills tileset was updated at the time this demo was compiled?

Also, the Under Ground Zone Act with the forts has some seriously odd mine-cart track placement - I wonder if the mine-cart gimmick wasn't part of their initial plan for the Zone? The layout suddenly seems to make a lot more sense if you imagine all the rails replaced with bricks. Is it possible the layout was made before the mine-cart rails existed, and then the metatiles were updated when the gimmick was thought of to allow for the other Act layout shown off in the autodemo to be created?