Background

A rhythm game is a genre of video game that focuses around the game playing a song, and having the player react in some way in time with the beats of the song. For example, some well-known rhythm games are Dance Dance Revolution, Guitar Hero, and Rhythm Heaven.

One rhythm game that has risen to infamy in recent years is osu!, pronounced "oss", rhymes with "moss". osu! has four game modes: "osu!", where the player aims at and clicks circles to beat (the most popular mode by far), "osu!mania", where the player presses keyboard keys in time with vertically scrolling notes (the next most popular mode), "Taiko", where the player hits different parts of a virtual drum in time with horizontally scrolling notes (not popular), and "catch", which involves moving a basket left or right to catch falling fruit (not popular).

In this post I will only be discussing osu!mania since it is the mode that I play.

Vertical scrolling rhythm games

osu!mania is a fairly typical VSRG (vertical scrolling rhythm game). The notes fall from the top of the screen towards the bottom, staying within their lanes. At the bottom are the receptors. When the note lines up with the receptor (in this screenshot, when it lines up with the blue-grey area) you press the key on your keyboard that corresponds to that receptor. In the screenshot there are 8 receptors, and so there are 8 keyboard keys associated with them.

Generally the timing of when you press the key is in time with a beat, syllable, or sound effect in the song.

For every note you are awarded a score depending on how accurately you hit it. In the screenshot, the number 300 is visible, which is the score of the note that was just hit.

The person who creates a beatmap for a song decides how many keys they want it to be played with, and then they time and map notes for those keys.

I would consider myself to be good at this game. I used to be ranked around #3500 in the world and placed #12 of 24 players in an Australia/NZ tournament back when I played the game more seriously. My complaints do not come from a place of salt because I am bad at the game.

Online rankings

osu! is online. Whenever you complete a song, your score is submitted, and you are ranked against every person who has played that map so you can see how you did against the world. Pretty standard feature.

A less standard feature - in fact, the only other rhythm game I know of with a similar feature is Quaver - is the performance points system. The PP system enables players to compare their skill without having to have played the same songs as each other. This means that you can see your overall ranking in the entire world, without having to have played the same songs as the entire world. So how does it work?

When you complete a song, an algorithm takes several factors about your play to decide how many pp your play was worth. These factors include:

• What was your score? Higher scores get more pp.
• How difficult was the map? Harder maps have a higher pp ceiling. Map difficulty is automatically calculated by the game, and is called "star rating".

Then, all of your plays ever that have earned pp are arranged from most pp to least pp, and are weighted as such:

• #1: pp x 1 = final pp
• #2: pp x 0.95 = final pp
• #3: pp x 0.9 = final pp

And so on.

Finally, all of the "final pp" values are added together, which makes your total pp for your account.

If you replay a map, and get more pp than before, your new play overwrites your old play in the chart.

If you play a new map and do very well, and it gets #1 on your pp chart, all your other plays get shifted down one spot to accommodate it.

Now you know the concepts. I'll talk more about this system in a bit.

Why is osu! popular?

osu! is accessible. It is free to play. It runs on Windows PCs and has very low system requirements. Hundreds of thousands of beatmaps (beatmaps are songs + timings + beat locations: a playable song in game) are freely downloadable from the official game website. It has an easy to use interface. All of this means that anybody can easily get into the game and hopefully somewhat enjoy themselves.

This is in stark contrast to the competition: most other VSRGs are either optimised for dance pads, are only available in Japanese, have a small song library, or have a bad user interface. Sometimes multiple of the above. Unfortunately none of the names of those games come to mind at the moment.

(Quaver is looking pretty good - hopefully it shakes up the situation and makes it so that there's finally another viable VSRG.)

So what's the problem?

osu!mania has a lot of weirdness and a lot of bad design going on. My personal theory is that the game's creator went to university for UI design, then tried to get a job as a UI designer, and couldn't. So they decided, "fuck it, let's make a rhythm game. Pretty simple concept. How hard could it be?" having never played a rhythm game before, and not knowing what makes one good.

Unusually, I'll write this post in approximate order of what I believe to be the most critical flaws to the least critical flaws.

No key count rankings split

• first hour: understand what you are seeing, learn to press the keys well
• next several hours: recognise common patterns in maps, learn them, and hit them out when you see them
• afterwards: how fast can you physically move your fingers?

With 7k, the skills needed that hold players back go something like this:

• unknown amount of time: correctly read the chart and press the correct keyboard key in response to a note
• I have not gotten past that barrier in 7k so I can't tell you what comes next, but it seems like a pretty big barrier

In short, being good at one key count does not help you at all in the other key counts.

So what any sane game would do is divide off the different key counts from each other. Select in the menu your preferred key count, and the game will only show maps for that key count, and when you earn pp your account has different numbers for all the different key counts.

osu!mania does NOT DO THIS.

In the song selection, all songs are shown in the same list, no matter their key count, so you have to pick through them and find the kind that you want to play, unless you know the secret code to type into the search bar, key=4, which filters by key count. It isn't explained in game that you can do that.

In online rankings, you have one pp number for the entirety of osu!mania. Earned some pp in 4k? It goes towards the global leaderboard. Somebody else earn pp on a 7k map? It goes towards the same global leaderboard.

YOU ARE COMPETING AGAINST PEOPLE WHO ARE PLAYING DIFFERENT GAMES.

Thank you, osu!mania.

Star rating and pp calculation

Star rating is the game's automatically calculated rating of how difficult a map is. This star rating is used to give your a heads up before you select the song, so that you don't have to play something that's far too easy or far too hard.

It's also used in pp calculation. The harder the song is, the higher the pp ceiling for plays on it.

This would be fine if the star rating calculation was good. It is not.

As far as I can tell, since I don't believe the algorithm is published, star rating is purely based on the highest number of notes per second in the map. From a naive perspective, this is reasonable - more difficult maps will have the player pressing more keys per second. Unfortunately, this idea ignores both (a) how music design works (b) how the human hand works.

How the human hand works:

Let's assume we're playing with 4 keys. Each finger would have a dedicated key in a horizontal row on the keyboard. It's sensible to play with your strongest fingers: left middle finger, left index finger, right index finger, right middle finger.

Now, imagine playing this pattern. X indicates a note to hit, - indicates the receptors, | indicates the gap between lanes.

| X |   |   |   |
| X |   |   |   |
| X |   |   |   |
| X |   |   |   |
| X |   |   |   |
| X |   |   |   |
| X |   |   |   |
| X |   |   |   |
|---------------|
| ^   ^   ^   ^ |

You would have to hit all of those notes with the same finger. How fast can you tap one finger?

|   | X |   |   |
|   |   | X |   |
|   | X |   |   |
|   |   | X |   |
|   | X |   |   |
|   |   | X |   |
|   | X |   |   |
|   |   | X |   |
|---------------|
| ^   ^   ^   ^ |

Assume that these notes fall at the same speed as in the above chart. This means that you can alternate hitting them with either hand: left index, right index, left index, right index. This means that the strain on each individual finger is halved. Halving the effort of something is a big deal.

Measured in notes per second, you can hit twice as many notes per second when they're arranged across both hands.

And the star rating calculator operates based on peak notes per second.

Consider long notes are relatively difficult to hit, especially when there are long notes falling in all columns at the same time, which must be pressed and released with different times. It's a less rarely used skill, and it requires a great deal more coordination. (If you don't believe me, try it yourself!) Comparatively, long notes are underrated in difficulty by the star rating algorithm.

Also underrated is so-called "technical maps", which are maps that have irregular timings of beats. They are still in time with the song, but the song is erratic, and the map matches it. Compare with a repetitive drum & bass rhythm. Songs like these allow the mapper to create something unusual, unique, and difficult to play. Tech maps unfortunately tend to be underrated in difficulty by the algorithm.

• The Flashbulb - Black Lawn Finale
• A StepMania map of the same song, demonstrating irregular note timings

What does this mean? It means that you comparatively earn less pp for the more interesting tech maps, which means your global ranking is not improved by playing them, which means that the game encourages playing the same 170 bpm anime intros for eternity. Tech maps get fewer plays, which demotivates mappers who might be thinking of creating maps for those kinds of songs. It's very unfortunate.

It means that not all maps are created equal in terms of how optimised they are for effort vs payoff in advancing up the global rankings.

In osu!'s circles mode, which gets more attention, the algorithm is occasionally adjusted to make the most farm-y maps less farm-y. In osu!mania, this problem has always existed, and the algorithm hasn't changed in a long time.

Thank you, osu!mania.

Now, there's one more part to this story. Star rating is based on peak difficulty, even if the difficulty only spikes for a couple of seconds. Interestingly, the intensity of music also commonly spikes for a couple of seconds! It's called a "drop", and it's commonplace in the genres of songs that are represented in a VSRG. When going from a proverbial "verse" to a "chorus", there's a moment of intensity in the song, often lots of rapid rhythmical drum beats before it settles back into a tune.

Of course, map creators want to represent those drum beats with a more intense and regular note pattern. And there's one note pattern that almost everybody opts for in moments like these.

| X | X |   |   |
|   |   | X | X |
| X | X |   |   |
|   |   | X | X |
| X | X |   |   |
|   |   | X | X |
| X | X |   |   |
|   |   | X | X |
|---------------|
| ^   ^   ^   ^ |

Yep.

There's a song and beatmap called "Swampgator" which has 2 sections in it, each 2 seconds long, that are mapped like that during a musical drop. Just 2 seconds each. I opened the beatmap editor and removed them. The overall star rating for the map dropped from 5.69 to 4.8 as a result. That is unbelievably stupid.

If you need me to explain why this is bad, it's because the rest of the map is comparatively easy to play, allowing you to get a good score, and just tank your way through the drop sections doing your best because they're not that hard or long, and so will most likely not reduce your HP to zero.

This means that you can get a great average score because you did very well on the other 98% of the map, and those 2% inflated the difficulty. The game thinks you got a great score on a hard map and awards you all the pp in the world for it.

There are many examples of this, Swampgator is nothing particularly special.

Thank you, osu!mania.

Pausing

Oh no, there's a section of the map that's quite intense and requires a lot of physical energy to play it, but it's also 3 minutes long and you don't have the stamina to not be reduced to a quivering mess by the end! What do you do?

You pause the game and stretch your fingers for 20 seconds, then unpause the game and continue without missing a note.

Pausing is considered among rhythm game communities to be a Bad Thing, since stamina is a skill in its own that can be trained and improved, but since there's no punishment in osu!mania for pausing partway through a song, and there is great reward...

¯\_(ツ)_/¯

Other games, like Quaver, deal with this brilliantly. They mark your score as having paused, and they don't let you upload it to the online boards. This is a perfect solution, and it's something that any rhythm game developer should have thought about if they had actually PLAYED A RHYTHM GAME for more than about 2 hours.

Note scoring

In all rhythm games, hitting a note gives you a score for that note. In osu!mania, the possible scores are:

• Rainbow 300. The best possible timing. This is very difficult to get for every note in a song, but it is humanly possible.
• Gold 300. Almost the best possible timing. It's reasonable to get all rainbow/gold 300s in a song if you're extremely capable of playing the song.
• 200. Your timing was a little off. Getting all 200s or better in a song is not terribly difficult if you are consistent enough to not drop a note by accident.
• 100. Your timing was pretty bad.
• 50. Your timing was terrible, but the game's gonna give it to you anyway.
• Miss. You didn't press the button within the timing window.

So you would assume that, since the game has a numerical counter for total score, and that individual notes also give a numerical score, that... the value of the note score is the contribution towards the total score.

This is not so.

The maximum possible score for any song is 1,000,000 points. Yes, for any song. The number of points you get for each note is not that actual number, but it's rather weighted by some constant value to give you the exact number of points you need to be able to make it to 1,000,000.

Except also not really. See the rainbow 300? If you say that the gold 300 is really worth 300 points, then the rainbow 300 is actually worth about 320 points in comparison. Yes, really. The number 300 is not the same as the number 300.

Except that it's even worse. The number of points you get for a note is not necessarily directly proportional to the note's value, because osu!mania has a very slight, but definitely existing, internal rolling combo system, which is different from the normal combo that you see.

If you get gold/rainbow 300 for a note, the internal rolling combo increases. If you get 200 or lower, the internal rolling combo decreases. This all gets put into an overcomplicated formula which spits out the actual score for the note.

The actual formula is shown here.

And after all of that effort, the score that it spits out is so irrelevant that professional players just use the value from the accuracy meter to judge well they did instead.

Thank you, osu!mania.

Timing leniency

At high level 4k play, there are a lot of notes on screen that all need to be hit. There are so many notes on screen that the timing windows for when they can be hit begin to overlap.

Compared to the note density, the timing windows are so lenient that the game becomes less about actually pressing the correct key to the rhythm and more about how well you can spam your keyboard at approximately the right frequency.

This is a problem for all VSRGs, but osu!mania doesn't even attempt to overcome it. Other games might have your life bar decrease drastically for many poor inaccurate hits in a row, so that you fail the song. Other games make it count as a miss if you press a key when there are no notes in that column within hitting distance, so that spamming the air with disregard for the note arrangement is heavily punished. osu!mania does not do either of those things.

This takes a lot out of the fun out of the game at a certain level of play.

Note colours

In osu!mania, the colour of each note depends on its column. All notes in the same column are the same colour.

What good rhythm games do is they set the colour of the note to its timing. If a note is pressed on the main beat of a song (aligned with a 1/4 beat, in musical terms) the note is red. If the note is aligned with a 1/8 beat it is blue. If it is aligned with a 1/16 beat it is yellow.

This is good because it lets people tell the timing of a note based on its colour, rather than trying to tell the exact distances of moving objects. If you're seeing red/yellow/blue/yellow/red over and over again then you know that it's very regular timing. If you see red/yellow/yellow/red then you know that there's a 1/16 gap in between the two yellows. And if it changes from red/yellow/blue/yellow/red to red/green/green/red then you know that it's about to change from a regular beat to triplets, which have a very different timing to be hit accurately, but look similar enough while scrolling that you might not notice that it's changing until after you actually hear the music change and your hits start being mistimed.

Note colours based on timing are a subtle but extremely helpful feature for a VSRG to have.

Converts

For some reason, osu! tries to automatically convert beatmaps that were created for the circles mode into beatmaps that can be played in mania mode. These beatmaps are bad because they are created by a computer with no concept of what makes a mania beatmap fun to play. Please take my word for it.

These bad beatmaps can only be removed from the song selection list by doing one of these three things:

• Delete every circles mode map from your computer.
• Type key=4 (or another number) into the search bar. It is not explained in game that you can do this.
• Type mode=m into the search bar. It is also not explained in game that you can do this.

Searches don't save if you exit the game, so you'll have to type this in every time.

There is no reason for converts to still exist in <current year>. Nobody likes them. But they're still in the game for some reason.

Thank you, osu!mania.

Long note combo counting

After you press a long note, the combo counter ticks up continuously as you continue to hold it. This is fun, I suppose, but it starts ticking after you press the note, rather than when the note actually is. This means that people who successfully hit every note in the map (known as a "full combo" in rhythm game communities) might actually have a different final combo number at the end of the map, depending on their timing. Kind of ruins the meaning of a "full combo" if it's a different number.

Conclusion

I don't think osu!mania is a very good game. I think it could have been much improved if it was developed by a person who had actually played a rhythm game before.