Beatmap Editor

A React component library for editing 5-lane rhythm-game beatmaps. Ships as an npm package, a UMD bundle, and a framework-agnostic Web Component.

• Demo: https://gamewota.github.io/beatmap-editor/
• npm: @gamewota/beatmap-editor
• Source: https://github.com/gamewota/beatmap-editor

Install

npm install @gamewota/beatmap-editor

Peer dependencies: React 18 or 19.

Quick start

import { useState } from 'react'
import { BeatmapEditor, Note } from '@gamewota/beatmap-editor'
import '@gamewota/beatmap-editor/style.css'

function App() {
  const [notes, setNotes] = useState<Note[]>([])

  return (
    <BeatmapEditor
      duration={180}            // seconds
      bpm={175}
      offsetMs={670}            // ms before first beat
      snapDivision={8}          // 1/8 grid (default)
      notes={notes}
      onNotesChange={setNotes}
    />
  )
}

Click a lane to place a tap note. Right-click a note to delete it. Pick Hold, click once to set the start, click again on the same lane to set the end.

Features

• Canvas-based timeline with batched rendering (handles long songs without UI lag)
• Sub-beat grid: visible subdivisions follow the snap setting (1/1 → 1/16)
• All note placement always snaps to the grid — no off-grid notes
• 5 lanes, tap + hold notes with cross-note links
• Audio waveform display with shared zoom/scroll
• Preview SFX on playback
• Exports to a JSON schema designed for game runtimes (see below)
• Available as React component, UMD bundle, and Web Component

Beatmap JSON schema

The editor reads and writes this exact shape:

{
  "bpm": 175,
  "offset": 670,
  "charts": [
    {
      "uuid": "807c1493-05a8-46e8-ae11-e2bca474d5f1",
      "laneCount": 5,
      "notes": [
        { "uuid": "...", "songPos": 0,    "beat": 0, "label": "", "lane": 1 },
        { "uuid": "...", "songPos": 1371.4285714285713, "beat": 4, "label": "", "lane": 3 }
      ],
      "links": [
        {
          "uuid": "...",
          "startNote": { "uuid": "...", "songPos": 27428.57, "beat": 80, "label": "", "lane": 0 },
          "endNote":   { "uuid": "...", "songPos": 28800.00, "beat": 84, "label": "", "lane": 0 }
        }
      ]
    }
  ]
}

• songPos is in ms relative to offset (audio time = songPos + offset).
• beat = songPos / (60000 / bpm) (fractional values are allowed for sub-beat snaps).
• lane is 0-indexed (0 = leftmost, 4 = rightmost).
• Tap notes appear only in notes[]. Hold notes appear as two entries in notes[] plus one entry in links[] referencing them (full object copies, not pointers).

Full schema reference: INTEGRATION.md → Beatmap JSON schema.

Snap convention

The snap denominator follows music notation — it divides the whole note (1 measure in 4/4), not a beat:

Setting	Snap interval	Lines per measure
1/1 (Whole)	1 measure (4 beats)	1 — measures only
1/2 (Half)	2 beats	2
1/4 (Quarter)	1 beat	4
1/8 (Eighth)	1/2 beat	8 (default)
1/16 (Sixteenth)	1/4 beat	16

Sub-beat subdivisions are rendered as thin lines between measure and beat lines.

Docs

• INTEGRATION.md — props, types, complete examples, schema reference
• MICROFRONTEND.md — using the Web Component from non-React apps
• LIBRARY.md — building, contributing, and releasing the library

License

MIT