rosu-pp-js

Library to calculate difficulty and performance attributes for all osu! gamemodes.

This is a js binding to the Rust library rosu-pp through Wasm. As such, its performance is much faster than a native js library. Since Wasm is used as intermediate layer, Rust doesn't even need to be installed.

Usage

The library exposes multiple classes and interfaces:

Beatmap

Class containing a parsed .osu file, ready to be passed to difficulty and performance calculators.

The constructor takes an object of type Uint8Array | string representing the content of a .osu file and throws an error if decoding the beatmap fails.

⚠️WARNING⚠️

Due to current JavaScript oddities, Wasm is not always able to track down objects' lifetime meaning it is possible that memory of unused instances might not get cleared automatically. Hence, to not risk leaking memory, it is recommended to free Beatmap instances manually when they're no longer needed with the free(): void method.

To convert a beatmap use the convert(GameMode): void method. To check whether difficulty and/or performance calculation on a beatmap should be avoided, use the isSuspicious(): void method.

Beatmap provides various getters:

• ar: number
• bpm: number
• cs: number
• hp: number
• isConvert: boolean
• mode: GameMode
• nBreaks: number
• nCircles: number
• nHolds: number
• nObjects: number
• nSliders: number
• nSpinners: number
• od: number
• sliderMultiplier: number
• sliderTickRate: number
• stackLeniency: number
• version: number

Difficulty

Class to calculate DifficultyAttributes, Strains, or create gradual calculators.

The constructor takes optional DifficultyArgs

{
    // The type must be either
    //   - an integer for bitflags (see https://github.com/ppy/osu-api/wiki#mods)
    //   - a string for acronyms
    //   - a single mod object as described below
    //   - a sequence of types that deserialize into a single mod
    //
    // Types that deserialize into a single mod are
    //   - an integer for bitflags
    //   - a string for an acronym
    //   - a mod object
    //
    // A mod object must have an `acronym: string` property and an optional
    // `settings?: Object` property.
    mods?: Object,
    // Custom clock rate between 0.01 and 100
    clockRate?: number,
    // For osu!standard and osu!mania it's important to specify whether calculations
    // are for lazer or stable scores.
    lazer?: boolean,
    // Custom approach rate between -20 and 20
    ar?: number,
    // Whether given `ar` should be used as is or adjusted based on mods
    // i.e. `true` means "given ar already considers mods".
    fixedAr?: boolean,
    // Custom circle size between -20 and 20
    cs?: number,
    fixedCs?: boolean,
    // Custom drain rate between -20 and 20
    hp?: number,
    fixedHp?: boolean,
    // Custom overall difficulty between -20 and 20
    od?: number,
    fixedOd?: boolean,
    // Amount of passed objects for partial plays, e.g. a fail
    passedObjects?: number,
    // Adjust patterns as if the HR mod is enabled on osu!catch maps
    hardrockOffsets?: boolean,
}

The following methods are available:

• calculate(Beatmap): DifficultyAttributes: The difficulty attributes for the given parameters
• strains(Beatmap): Strains: The strain values for the given parameters, suitable to plot difficulty over time
• gradualDifficulty(Beatmap): GradualDifficulty: A gradual difficulty calculator
• gradualPerformance(Beatmap): GradualPerformance: A gradual performance calculator

Performance

Calculator of PerformanceAttributes whose constructor takes PerformanceArgs

{
    // ... same fields as for `Difficulty` but also:

    // Accuracy between 0 and 100
    accuracy?: number,
    // The max combo of a play
    combo?: number,
    // The amount of gekis (n320 for mania)
    nGeki?: number,
    // The amount of katus (tiny droplet misses for catch, n200 for mania)
    nKatu?: number,
    // The amount of n300s
    n300?: number,
    // The amount of n100s
    n100?: number,
    // The amount of n50s
    n50?: number,
    // The amount of misses
    misses?: number,
    // Legacy total score for osu! scores on stable
    legacyTotalScore?: number,
    // The amount of "large tick" hits.
    largeTickHits?: number,
    // The amount of "small tick" hits.
    smallTickHits?: number,
    // The amount of slider end hits.
    sliderEndHits?: number,
    // Whether good or bad hitresults should be generated to fit the given accuracy
    hitresultPriority?: HitResultPriority,
}

Its method setHitresultGenerator takes a HitResultGenerator and GameMode and defines what the focus of hitresult generation should be, e.g. performance or speed.

Its only other method calculate(DifficultyAttributes | PerformanceAttributes | Beatmap): PerformanceAttributes produces the performance attributes. The method's argument must be either the attributes of a previous calculation or a beatmap.

Note that if a beatmap is given, difficulty attributes have to be calculated internally which is comparably expensive so passing attributes should be prefered whenever possible.

However, be careful that the passed attributes have been calculated for the same difficulty settings like mods, clock rate, beatmap, custom ar, ... otherwise the final performance attributes will be incorrect.

GradualDifficulty

Class to calculate difficulty attributes after each hitobject.

Its constructor takes a Difficulty and a Beatmap, it has a getter nRemaining: number, and the methods

• next(): DifficultyAttributes | undefined: Process the next hitobject and return the difficulty attributes (or undefined if the last object has already been processed)
• nth(number): DifficultyAttributes | undefined: Process the next number - 1 hitobjects, i.e. nth(0) will process one, nth(1) will proces two, ...
• collect(): DifficultyAttributes[]: Collect all remaining difficulty attributes into a list

GradualPerformance

Class to calculate performance attributes after each hitresult.

Its constructor takes a Difficulty and a Beatmap, it has a getter nRemaining: number, and the methods

• next(ScoreState): PerformanceAttributes | undefined: Process the next hitobject and return the performance attributes (or undefined if the last object has already been processed)
• nth(ScoreState, number): PerformanceAttributes | undefined: Process the next number - 1 hitobjects, i.e. nth(0) will process one, nth(1) will proces two, ...

ScoreState is an object like

{
  maxCombo?: number,
  misses?: number,
  n100?: number,
  n300?: number,
  n50?: number,
  nGeki?: number,
  nKatu?: number,
  osuLargeTickHits?: number,
  osuSmallTickHits?: number,
  sliderEndHits?: number,
  legacyTotalScore?: number | null,
}

BeatmapAttributesBuilder

Class to calculate BeatmapAttributes for various custom parameters.

Its constructor takes BeatmapAttributeArgs

{
    // Start off with the given beatmap's attributes, mode, and convert status
    map?: Beatmap,
    // Specify a gamemode
    mode?: GameMode,
    // Whether the map is a convert, only relevant for mania
    isConvert?: boolean,
    mods?: Object,
    clockRate?: number,
    ar?: number,
    fixedAr?: boolean,
    cs?: number,
    fixedCs?: boolean,
    hp?: number,
    fixedHp?: boolean,
    od?: number,
    fixedOd?: boolean,
}

Its only method is build(): BeatmapAttributes.

Setters

For the Difficulty, Performance, and BeatmapAttributesBuilder classes, each field of their constructor's argument object is also available as a setter afterwards which takes either a value of the field's type or undefined to unset the previously set value.

import * as rosu from "rosu-pp-js";

// Either given in the constructor
let difficulty = new rosu.Difficulty({ clockRate: 1.23 });

// Or adjusted afterwards
difficulty.mods = 8;

// Or even reset entirely
difficulty.clockRate = undefined;

Examples

Calculating performance

import * as rosu from "rosu-pp-js";
import * as fs from "fs";
// or if you're using CommonJS:
const rosu = require("rosu-pp-js");
const fs = require("fs");

const bytes = fs.readFileSync("/path/to/file.osu");

// Parse the map.
let map = new rosu.Beatmap(bytes);

// Convert the beatmap to a specific mode for optionally given mods.
map.convert(rosu.GameMode.Mania, "6K");

// Whereas osu! simply times out on malicious maps, rosu-pp does not. To
// prevent potential performance/memory issues, it is recommended to check
// beforehand whether a map is too suspicious for further calculation.
if (map.isSuspicious()) {
    process.exit();
}

// Calculating performance attributes for a HDDT SS
const maxAttrs = new rosu.Performance({ mods: 8 + 64 }).calculate(map);

const perf = new rosu.Performance({
    mods: "HDDT", // Must be the same as before in order to use the previous attributes!
    misses: 2,
    accuracy: 98.4,
    combo: 567,
    hitresultPriority: rosu.HitResultPriority.BestCase,
});

// For hitresult generation, use the `setHitresultGenerator` method.
// The 'Closest' hitresult generation may be significantly slower but provides
// hitresults that match the given accuracy as close as possible.
perf.setHitresultGenerator(rosu.HitresultGenerator.Closest, rosu.GameMode.Osu);
// Especially for mania, 'Closest' might be too slow in general so let's use
// 'Fast' instead (which is the default anyway for all modes if unspecified).
perf.setHitresultGenerator(rosu.HitresultGenerator.Fast, rosu.GameMode.Mania);

// Calculating performance attributes for a specific score.
const currAttrs = perf.calculate(maxAttrs); // Re-using previous attributes to speed up the calculation.

console.log(`PP: ${currAttrs.pp}/${maxAttrs.pp} | Stars: ${maxAttrs.difficulty.stars}`);

// Free the beatmap manually to avoid risking memory leakage.
map.free();

Gradual calculation

import * as rosu from "rosu-pp-js";
import * as fs from "fs";

const content = fs.readFileSync("/path/to/file.osu", "utf-8");
const map = new rosu.Beatmap(content);

// Specifying some difficulty parameters
const difficulty = new rosu.Difficulty({
    mods: 16 + 64, // HRDT
    clockRate: 1.1,
    ar: 10.2,
    fixedAr: true,
    od: 4,
    fixedOd: false,
});

// Gradually calculating *difficulty* attributes
let gradualDiff = difficulty.gradualDifficulty(map);
let i = 1;

while (gradualDiff.nRemaining > 0) {
    console.log(`Stars after ${i} hitobjects: ${gradualDiff.next()?.stars}`);
    i += 1;
}

// Gradually calculating *performance* attributes
let gradualPerf = difficulty.gradualPerformance(map);
let j = 1;

while (gradualPerf.nRemaining > 0) {
    // Need to pass the current score state
    const state = {
        maxCombo: j,
        n300: j,
        n100: 0,
        // ...
    };

    console.log(`PP: ${gradualPerf.next(state)?.pp}`);
    j += 1;
}

map.free();

Installing rosu-pp-js

$ npm install rosu-pp-js

or

$ npm install https://github.com/MaxOhn/rosu-pp-js/releases/download/v4.0.1/rosu_pp_js_nodejs.tar.gz

Note that apart from the *_nodejs version, the release page also includes *_web and *_bundler versions.

Learn More

• rosu-pp
• Rust
• Wasm