Closes https://github.com/ppy/osu/issues/28369.
The reporter of the issue was incorrect; it's not the beat snap grid
that is causing the problem, it's something far stupider than that.
When the current selection changes,
`EditorSelectionHandler.UpdateTernaryStates()` is supposed to update the
state of ternary bindables to reflect the reality of the current
selection. This in turn will fire bindable change callbacks for said
ternary toggles, which heavily use `EditorBeatmap.PerformOnSelection()`.
The thing about that method is that it will attempt to check whether any
changes were actually made to avoid producing empty undo states, *but*
to do this, it must *serialise out the entire beatmap to a stream* and
then *binary equality check that* to determine whether any changes were
actually made:
7b14c77e43/osu.Game/Screens/Edit/EditorChangeHandler.cs (L65-L69)
As goes without saying, this is very expensive and unnecessary, which
leads to stuff like keeping a selection box active while a taiko beatmap
is playing under it dog slow. So to attempt to mitigate that, add
precondition checks to every single ternary callback of this sort to
avoid this serialisation overhead.
And yes, those precondition checks use linq, and that is *still* faster
than not having them.
Reported in https://discord.com/channels/188630481301012481/1097318920991559880/1221836384038551613.
Example score: https://osu.ppy.sh/scores/1855965185
The cause of the overestimation was an error in taiko's score simulator.
In lazer taiko, swell ticks don't give any score anymore, while they did
in stable.
For all intents and purposes, swell ticks can be considered "bonus"
objects that "don't give any actual bonus score". Which is to say,
during simulation of a legacy score swell ticks hit should be treated
as bonus, because if they aren't, then otherwise they will be treated
essentially as *normal hits*, meaning that they will be included in
the *accuracy* portion of score, which breaks all sorts of follow-up
assumptions:
- The accuracy portion of the best possible total score becomes
overinflated in comparison to reality, while the combo portion of
that maximum score becomes underestimated.
- Because the affected score has low accuracy, the estimated accuracy
portion of the score (as given by maximmum accuracy portion of score
times the actual numerical accuracy of the score) is also low.
- However, the next step is estimating the combo portion, which is done
by taking legacy total score, subtracting the aforementioned
estimation for accuracy total score from that, and then dividing
the result by the maximum achievable combo score on the map. Because
most of actual "combo" score from swell ticks was "moved" into the
accuracy portion due to the aforementioned error, the maximum
achievable combo score becomes so small that the estimated combo
portion exceeds 1.
Instead, this change makes it so that gains from swell ticks are treated
as "bonus", which means that they are excluded from the accuracy portion
of score and instead count into the bonus portion of score, bringing the
scores concerned more in line with expectations - although due to
pessimistic assumptions in the simulation of the swell itself,
the conversion will still overestimate total score for affected scores,
just not by *that* much.
