Battletoads first tunnel

[Zelex]

Battletoads has a peculiar problem where the game is emulated perfectly until the first vertical tunnel. You go down the tunnel and if your character touches the bottom pixel he disappears, and your rope disappears. You can still play the game and move left and right (and the mosters will continue to look at you), but you can't come back up. Eventually your character dies and you start back at the top, but then you can't kill any enemies and as such the level never ends. I've had problems with this tunnel in at least 2 emulators that I've written. This new emulator does better and gets further, but this tunnel is ridiculous. There has to be a simple explanation of what its expecting in terms of accuracy and what I'm not doing. Any ideas or suggestions on where to look specifically?

[3gengames]

Can you make a video of how to do the glitch? I've never heard of this glitch.

[rainwarrior]

Your character should not be able to go off the bottom of the screen, there is normally a little bounce reaction that bumps you up if you go all the way down. I can't really speculate how your emulation would fail to make that happen though.

[Dwedit]

Battletoads really doesn't like it when you press Up and Down at the same time.

[blargg]

Left and Right as well. I remember spending quite a bit of time chasing down a bug where the toad rose and stayed higher off platforms in the snake level, due to pressing left and right at the same time as I playtested.

[tokumaru]

Battletoads has a peculiar problem...

No it doesn't, your emulator does!

In all fairness, the game does have that terrible two-player mode bug that makes it impossible to complete, but that's not the one you were talking about. =)

[Bananmos]

> In all fairness, the game does have that terrible two-player mode bug that makes it impossible to complete

Just want to point out that the PAL version does not, so we European kids were saved of this disappointment if we were lucky enough to have a friend as OCD:d as us to play it in two players with. Still, the difficulty increase you get from two-player mode makes the game virtually impossible to complete anyway without game genie cheats. Though I would love to have a go at this with another skilled and infinitely patient Battletoads fan sometime...

[Zelex]

Battletoads has a peculiar problem...

No it doesn't, your emulator does!

In all fairness, the game does have that terrible two-player mode bug that makes it impossible to complete, but that's not the one you were talking about. =)

Yeah, thats what I was implying. I'm just curious as to what that tunnel does that is special, other than the parallax scrolling stuff (as that works fine).

If nobody has any ideas, np. I'll debug it and put it in this thread for future reference for future NES emu developers if they experience similar problems.

[rainwarrior]

Two of the levels disabled rendering during vblank and let it run long for extra CHR-RAM upload time, leaving a noticeable extended black bar at the top of the screen (the snake level, and the revolution). I don't know if this is the case for the turbo cables level, but maybe it runs a few lines over, unnoticeable to the eye (but would make a significant difference to the emulator of course). The game always has at least one row of black tiles at the top of the screen, perhaps sometimes rendering is actually off during those rows.

[Zepper]

Isn't related with sprite zero hits?

[Zelex]

The problem looks to be pressing left+right or up+down at the same time. Pretty sure its fixed now.

Btw, thanks to you guys for the suggestions It shortened my time to finding the problem immensely.

[Zepper]

Ah... that problem. Yes, it's weird. In a few controllers, you're able to press up+down for example. It completely messes up the gameplay.

[Gilbert]

I think a number of other games have similar problems too. Unfortunately it's hard to classify whether this is a bug of the games, as they work on the original controllers (not broken ones, at least) and you could just say this is an oversight of the possibility of using a 3rd party controller.

At least it's not as ridiculous as Karnov, in which you commit suicide when you press A and B at the same time (and that's intentional most probably).

[LocalH]

Unfortunately it's hard to classify whether this is a bug of the games, as they work on the original controllers (not broken ones, at least) and you could just say this is an oversight of the possibility of using a 3rd party controller.

If the undesired behavior appears when running on authentic hardware from an authentic cart, then I say that it's a bug in the game (or in rare circumstances, perhaps an interaction between a game and a quirk of the hardware, although I'm not sure if there are any such situations in the NES/FC library). In such cases, if emulated or clone hardware does not reproduce the bug in the same way, then I consider it to be faulty with regards to the goal of accuracy.

[Zepper]

Zelda 2 has a similar problem with left+right.