osu! to osu!taiko conversion leads to mistimed hits

[Flan-Fan]

Type

Game behaviour

Bug description

There is a certain difficulty of a map (link that when played as a convert in taiko, the majority of notes seem to be mistimed. I've tested converting this beatmap to mania and catch, but they play fine.

This is not a lazer-only bug, as this also happens in stable (and is known within the convert community)

Screenshots or videos

No response

Version

2022.319.0

Logs

database.log
network.log
performance.log
runtime.log
updater.log

[bdach]

I am not sure much can be done about this. Looking at the map involved, sliders are being converted wonkily to hits, and as such the issue would have to be located in the part of the conversion algorithm concerned with converting sliders to hits, which is notoriously finicky and sensitive to floating point errors on stable and was attempted to be reproduced as closely as possible in lazer:

osu/osu.Game.Rulesets.Taiko/Beatmaps/TaikoBeatmapConverter.cs

Lines 148 to 150 in d681643

	// DO NOT CHANGE OR REFACTOR ANYTHING IN HERE WITHOUT TESTING AGAINST _ALL_ BEATMAPS.
	// Some of these calculations look redundant, but they are not - extremely small floating point errors are introduced to maintain 1:1 compatibility with stable.
	// Rounding cannot be used as an alternative since the error deltas have been observed to be between 1e-2 and 1e-6.

Changing anything there may change conversion results across many other beatmaps in a backwards-incompatible manner. Moreover I checked that lazer matches stable on the particular map you've linked 1:1, so this may be considered a "feature-not-bug".

[peppy]

Now that we have classic mod, we could potentially change the conversion strategy when the mod is not applied.

[smoogipoo]

I don't understand how the classic mod changes any of the above.

[peppy]

My thinking is that we can fix issues like the said map where conversion is objectively wrong (but we match it to support backwards compatibility). ie. introduce the breaking changes when classic mod isn't applied – use more correct conversion algorithms – but still maintain backwards compatibility on scores.

I migth be missing something though.

[smoogipoo]

Turns out I misunderstood the above issue, it's just mistimed hits and not incorrect conversion. Unsure whether the conversion algorithm should be tied to the classic mod, because it makes it very hard to change. Would prefer it being tied to beatmap versions instead, meaning that this map would not be fixed, along with a separate mod that can override the conversion algorithm version.

[Genjurowo]

Basically what is happening is slider ticks getting converted to circles in taiko which is intended behavior. Now the reason why the notes seem mistimed is because the mapper used slider tick rate 3, which is reserved for songs that primarily use 1/3 rhythms (example as this snaps the slider ticks on the 1/3 grid. The only real issue here is the map getting ranked with these settings

[bdach]

Based on the above explanation I think this can be closed. Not much we can do there, I'd say.