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07 — Roadmap

Each phase ends with something runnable on your phone. No phase depends on future phases to be testable.

Phase 0 — Project skeleton (½ day)

  • Create the Android project: Kotlin, Compose, min SDK 26, package com.felipeftn.magnusorgue.
  • Add NDK/CMake setup and the Oboe dependency; a native lib that just logs "hello".
  • Empty main screen with the app name.
  • Done when: ./gradlew installDebug puts a launchable app on the phone.

Phase 1 — Audio engine core (1–2 days)

  • Oboe stream (LowLatency/Exclusive, float, native rate).
  • Voice (sine only, fixed pitch) + envelope; VoiceManager with the 32-voice pool.
  • Lock-free event queue + the 7-function JNI bridge.
  • Temporary debug button in the UI: press = noteOn(60), release = noteOff(60).
  • Done when: pressing the debug button produces a clean, click-free tone with obviously low latency.

Phase 2 — On-screen keyboard (1–2 days)

  • KeyboardView in Compose Canvas: layout, hit testing, multitouch.
  • OrganController wiring touch → engine; pressed-key highlighting.
  • Octave shift buttons; landscape orientation; keep-screen-on.
  • Done when: you can play chords on the screen with both hands, no stuck notes, no clicks.

Phase 3 — MIDI over OTG (1–2 days)

  • MidiInputManager: enumerate devices, hotplug callback, open output port.
  • MidiMessageParser (+ unit tests: velocity-0, running status, multi-message packets).
  • Note events → controller → engine; MIDI-pressed keys light up on screen.
  • Status chip in the top bar; release device's notes on unplug.
  • Done when: plugging your MIDI keyboard via OTG plays notes with zero configuration, and unplug/replug works. This is the heart of the app — test hard here (see 08-testing.md).

Phase 4 — Organ voicing & stops (1–2 days)

  • Additive harmonics in Voice; define the 4 stops (Principal 8', Flute 8', Strings 8', Tutti).
  • Stop selector in the top bar; master volume slider with smoothing.
  • Panic button; audio focus handling; pause/resume engine with Activity lifecycle.
  • Done when: the 4 stops sound distinct and organ-like; 10-finger chords stay clean.

Phase 5 — MVP polish (1 day)

  • App icon, dark theme colors, MIDI-connected snackbar.
  • Error banner for audio-start failure; edge cases from 03-architecture.md.
  • Release build config (minify, signing for personal use).
  • Done when: a signed release APK you'd happily keep on your phone. 🎉 MVP shipped.

Post-MVP (P1) — in rough order

  1. Sustain pedal (CC 64).
  2. Settings screen + persistence (DataStore): velocity toggle, labels, channel, reverb.
  3. Simple fixed reverb (e.g., Freeverb port in the native layer).
  4. Glissando on the touch keyboard; note labels.

Future (P2) — ideas parking lot

  • Sample-based voices (swap Voice implementation) / SoundFont support.
  • Stop combination (multiple stops at once, drawbar-style).
  • Multiple MIDI devices as multiple manuals; BLE MIDI.
  • Foreground service for background audio; transposition; tremulant; historical temperaments.
  • Play Store release (privacy policy, store listing, screenshots).

Estimated total for MVP

~6–9 working days of focused effort (phases 0–5), heavily dependent on how much latency/device tuning Phase 1 needs.