ЭIИO2: Rebirth

This may not look like much, but this is the moment, after weeks of experimentation, when I was finally succeeded in editing the compressed art in the game. It might be a bit premature, but I think I've just busted the game wide open for an extensive art edit.

 

I cheated a bit. If you recognise the art, you'll know that it's the moving platform from scrambled egg zone, which is stored as compressed art in the game but it's actually 0% compressed. I copied that data to an unused spot and changed the dropped ring compressed art pointer. Sounds really simple, but there were lots of little things I had to figure out and mistakes to correct to make it work. All the info has already been discovered here, it just took me a while to get my head around it. The master system environment is a lot more hostile to hacking than the mega drive environment. One of the mistakes I learnt is that you can't have data overlapping between two different $4000 segments

 

Yeah, that's not really what I had problems with, it was more the pointer editing and rejigging the headers and the footers of the compressed art. I didn't discover anything new, I just understand it now. I plan to just store new art uncompressed though, because I couldn't be arsed compressing it, and it allows me to just edit it directly if I want to change anything.

 

You see that! That's the smiley face of victory! You're my bitch now, devil rom! Cower before your master! Mwahahahahaha!

 

<!--quoteo(post=211983:date=Jul 29 2008, 05:26 PM:name=ICEknight)--><div class='quotetop'>QUOTE (ICEknight @ Jul 29 2008, 05:26 PM)
You see that! That's the smiley face of victory! You're my bitch now, devil rom! Cower before your master! Mwahahahahaha![/quote]Good work, dude. This might also help locating any unused graphics.

Do you know if other GG Sonics share the same format?
[/quote]
I think all the unused graphics that can be found have already been found. If there is anything left to be discovered, it would be art that has been compressed but has not been loaded to vram during play. I'm not really interested in scouring through the code for any instances of that. Not at the moment anyway. Perhaps Hive has already done it when he was compiling the rom breakdown? This is more about applying the knowledge that we have to create an 8-bit sonic 2 hack.

I believe the 8-bit games do have the same format, based on this info

 

For those of you playing along at home

Compressed Art Template

01 00 NN NN PP PP [Art Data] [Compression definition]

01 00: This is the start. You need to change the pointer for the art you're inserting to the address of 01 byte
NN NN: This is the number of 8x8 tiles in your [Art Data] (in hexadecimal, of course). It is little endian, so the second byte is typically 00
PP PP: This is the relative pointer to the [Compression definition]. It is relative to the address of start and also in little endian
[Art Data]: This is the 8x8 tiles of your art. You can extract these uncompressed from a save state if you wish to edit the original art.
[Compression definition]: This defines what kind of compression is used for each tile. Each tile is defined by two bits. Uncompressed tiles are defined as 01. If all your tiles are uncompressed, the complete compression definition will be

(NN / 4) x '55'

e.g. 8 tiles will be followed by a compression definition of 08/4 = 2 bytes of 55 ie 55 55

 

BEFORE:


AFTER:


Hehe! Mappings are easy to edit too.

Special Thanks to Hive Brain, Rolken, and Ambil. All the work they have done is making this exceedingly easy for me. Why hasn't anybody tried it before?