Are there any hacks where 2 player gets their own view?

To be honest, I don't think anyone's bothered making a hack like this. The reason the water palette gets in the way is because you can only have it change once, as in, you can only have two halves of the screen, one using the water palette, the other using the air palette. You could either display water on the bottom screen and not the top, or you could display water on the top screen, but cause the entire bottom screen to have the water palette regardless of how much area of the bottom screen actually contains water.

 

Technical limitations aside, it'd be a bitch to test, and there would be much more to keep in mind when designing levels. Some of the vertical wrapping bits of S3K would be downright impossible to use, if it includes any racing then you'd have to keep a close eye out for balance issues (nothing like items making a lead too easy to keep), single-use switches or drops that would need re-enabled for the second player, etc. All around, there are just too many extra hurdles that nobody really wants to worry about.

That being said, a Sonic hack in the same vein as Four Swords would be awesome if it could be pulled off. But I don't think anybody wants to put in the effort.

 

Since Sonic 2 loads every object in the vertical column the screen is at, wouldn't using the Sonic 3 method of loading objects make things much faster?

 

Definitely, and it's the only way to make a busy level such as Metropolis even work at a decent rate. I think flamewing had to implement the Sonic 3 object manager because of the increased overhead of having three characters at the same time in Sonic 2 Heroes. But I'm pretty sure that in 2P mode, the game would still slow down when somebody loses all of their rings, gets invincibility, etc, regardless of whatever tricks you pull.

As for the original game and its odd pick of levels, it actually makes more sense when you think about the ones they left out:

• Chemical Plant has water (in Act 2, anyway), which is problematic due to the mid-scanline pallete switch trickery, as noted above.
• Aquatic Ruin has water too.
• Hill Top does a lot of crazy things with the background layer to simulate moving ground and lava.
• Oil Ocean... well, I can't think of anything but the oil at the bottom of the screen, which may very well be a non-issue.
• Metropolis is a vertically-wrapping level, which would likely require specific code to work correctly in 2P mode.

Emerald Hill, Casino Night and Mystic Cave aren't so much random picks as they are "safe" choices, with not much in the way of nonstandard level gimmicks.

 

It's possible to change the palette as many times as you want, provided you have enough access slots (in H40 mode, there are 18 writes every scanline outside vblank), and you don't mind CRAM dots (I.e. garbage color on screen when it's writing outside hblank).

The real issue here is that the raster effect code isn't designed to handle water and split screen at the same time, plain and simple. Doing that requires writing new code.

 

A co-op Sonic hack would be interesting. If it was down to me, I'd actually do it like Sonic 3's co-op, but have certain areas impossible to progress without a second player and have that as the main focus.

 

It's actually possible to play any Sonic 2 level in 2p mode thanks to hacking or Game Genie codes (as well as take out water so aformentioned levels can work) however the experience is still barely playable due to garbage graphics covering both screens and the 2P screen often suffering delay. Also as mentioned not as many objects load in split screen which can lead to important platforms or springs, etc being absent preventing you from progressing any further.

Hill Top suffers the least graphic problems and thus is nearest to playable, however it still suffers due to earthquakes and doors not activating for Tails and an important spring not appearing in Act 2.

 

There is only one game to date that I know for a fact uses seperate screens for it's 2-Player mode, and that's Zero Tolerance. It relies off using a specialized double-ended "link" cable that's simply two Mega Drive/Genesis joypad connections that's been rewired to send input/output through each console. The schmatics are still available on Technopop's website.

http://www.technopop.net/

The only thing that needs to be worked out is the "code" to get both systems to see each-other as well as know the input/output method. It shouldn't be that difficult given the fact we have a lot of bright coders here who would take the challenge.

 

And two TVs =P

Alternatively, two Nomads. I swear, considering how it handles the 2P port, that'd make it a perfect fit - it literally becomes a link cable. I wonder if anybody played Zero Tolerance like this. It'd be nice to know if there's a way to detect a Nomad though =/

 

It goes from player 1's second port to player 2's first port, then?

I can see how that would be an issue.

 

Huh, I thought it was 1P port for the joypad and 2P port for the link cable on both systems (because, you know, you need to plug in the second joypad somewhere...). Unless it's some hardware incompatibility and not that (like with Decap Attack, which doesn't work on Nomads because its joypad routine does something it shouldn't apparently).

EDIT: Tiido says it works fine with Nomads...

 

It would be interesting to play the normal game in co-op using two nomads for sure. It would get rid of the water issue. only thing with the actual game that would need modification (aside for the link cable code) would be to enable tails to smash monitors, activate switches and the like. Would be fun.

 

Actually, you need to ensure they stay in sync if one of them slows down for whatever reason (not to mention that eventually they will go out of sync because oscillators aren't perfect). Also, since you have two separate consoles, you may as well modify the object manager to let them handle two completely different set of objects when players are far enough from each other.

EDIT: also the fact that even if the oscillators were perfect, you can't know what is each VDP doing. One of them could be in vblank while the other could be in the middle of the screen, for example =P

 

If it hasn't been mentioned, why not a hack that completely re-designs 2P vs mode from scratch [or near scratch] so instead of working with the existing system, you [whoever that would be] would be making a new system that could fully take advantage of, push the Megadrive hardware to the limit?

 

Didn't the Mega Collection version of Sonic 2 use some sort of different rendering for split screen?

 

Implying SEGA could possibly have been bothered to do this when the rest of the collection was entirely emulation.