Sonic 2: S3 Edition

I still can't seem to get level select to work. I've put in 1-9-8-2, pressed start, then hold a+start [that *is* how it's done, right? haven't used it for so long! - ie. haven't needed to]

 

I just have a question..

Could you update the link?

It leads me to a blank page.

 

Hint: Alrightyman, put the working link in the first post, be a dear.

Have there been any other updates recently?

 

I found the link on the 2nd page. Silly me.

The hack has a weird bug that freezes the game sometimes after an act is completed.

Just for reference.

 

This isn't exactly correct, or at least it wasn't clear what you meant. All the graphics are the same size as they are in the normal levels. What's happening is that Sonic 2 is using the Genesis' double-resolution mode, which will output graphics as if the resolution were doubled. In other words, when it grabs the graphics data in VRAM, it interlaces those graphics into the final 8x8 cell. This is what causes the squished effect in the 2P mode. The thing is, since the Genesis *still* has to maintain it's 8x8 cell structure when displaying graphics on screen, it has to treat every two tiles in VRAM as a single cell while in double-res interlaced mode. The top four lines of the cell are interlaced from the first VRAM tile, while the bottom four are interlaced from the second tile. WHat this also means is that the way the tiles are referenced by the nametable is completely different. Also note that even though it's called "double res" mode, this isn't technically the case. The nametable structure is still exactly the same, the main difference being that each 2-byte tile reference in the nametable will draw the "equivalent" of 16 pixels vertically instead of 8. For the record, this is why this routine exists in S2:

Code (Text):

1.     lea (Block_Table).w,a1
2.     move.w  #$BFF,d2
3.  
4. loc_E41A:
5.     move.w  (a1),d0
6.     move.w  d0,d1
7.     andi.w  #$F800,d0; filter for upper five bits
8.     andi.w  #$7FF,d1; filter for lower eleven bits (patternIndex)
9.     lsr.w   #1,d1; dunno what this is about
10.     or.w    d1,d0
11.     move.w  d0,(a1)+
12.     dbf d2,loc_E41A

(found in loadZoneBlockMaps if you're using the newest disasm)

Since in double-res mode every two tiles in VRAM is treated as a cell, the patternIndex counts by every TWO tiles instead of one. So if patternIndex were 4, it'd be referencing the eighth tile in VRAM, not the fourth as normal. Thus, when playing a 2-player stage in Sonic 2, it has to go through the 16x16 blocks and divide the patternIndex part of the word by 2.

As for the 16x8 blocks you referred to? The original 16x16 blocks are basically just a list of four nametable entries arranged as a square (or "block", thus the name), with each entry drawing an 8x8 tile. However, as I said, in double-res mode each nametable entry uses two tiles for a cell, arranged vertically (turning an 8x16 "tile" into an 8x8 cell). This means that for a given 16x16 block, you only need to put two nametable entries instead of 4 to produce an equivalent 16x16 tile on screen (or, since it's been interlaced, a 16x8 tile in the end). The game just so happens to use the first two nametable entries in a given 16x16 block. Obviously, this also changes the way the game updates the nametable as you move, but that's a relatively minor change and not hard to understand if you examine LoadTilesAsYouMove closely.

The last question is then how the graphics are displayed properly if the game simply ignores half of a 16x16 block definition? They arranged the VRAM tiles in a way so that it would work of course. Look at a sheet of the EHZ tiles, either in VRAM or TLP or wherever. Visualize every two tiles as a single 8x16 tile, both tiles being stacked on top of each other. What you visualize is exactly what the Genesis draws interlaced for every cell definition in the nametable. This is also why if you change and reorganize the EHZ tile sheet it'll look like a mess in 2P mode. You'll find a similar pattern in MCZ and CNZ.

Sorry for the long-winded explanation, although really I'm just explaining stuff that people before me already figured out. In fact, I think someone else made a much better explanation of this some time ago on these forums, though I can't remember when.

 

It was Nemesis, though most people here can't see his post.

 

Oh yeah that's done it for me, thanks alot

 

Is there a debug code, or is it the same as sonic 2?

 

Great hack! However I did notice a few problems.

Firstly, when I completed the EHZ Act 1 Boss sonic kept on walking on air and took a while to go back to normal. Secondly I can't get past ARZ Act 1. The first time when I passed the signpost the game froze, and the second time it just sat there as if nothing had happened (except it stopped the timer) and didn't bring up the score card.

 

brilliant!

I especially love the little detail of how the Electric Shield deflects the crab's claw in Metropolis.

 

Wow, this is fucking awesome!
You've seriously worked on this hack and I love how you ported the GHZ Boss and used it as a miniboss, in fact there hasn't been any minibosses in a Sonic 2 hack as far as I know. I attempted it but failed, as usual...
Anyway, great work! Looking forward to see your next work.

 

Very cool although was I the only one expecting to see sonic 2 sprites and visuals just running on the sonic 3 engine? This is the first time I seen this topic so my mistake.

 

Nice. I have a small problem in Genesis Plus (Mac Emulator) though. If I jump after hitting the first sigpost in Emerald Hill Zone, he plays his end of Act pose in mid-air, and then I can run on an invisible path in the air until I jump.

EDIT: Actually, I have a bigger problem. The transition between Aquatic Ruin 1 and 2 crashes the game. That is incomplete, right?

 

<!--quoteo(post=266262:date=Jan 11 2009, 05:46 AM:name=synchronizer)--><div class='quotetop'>QUOTE (synchronizer @ Jan 11 2009, 05:46 AM)

 

The GHZ mini-boss can still hit you when he's exploding.

When you're at the top, chemical plant's background glitches as seen in this vid: http://www.megaupload.com/?d=RRA9FZ7M (it's just over 1.3mb)

 

Awesome work, as always. Nice improvements since the last beta you sent me.