# SP-404MK2 layers

A combo trainer for the Roland SP-404MK2, wrapped as a sideloaded Android APK.

**Phase 1 (current):** the original single-file web app, wrapped in Capacitor as-is.
**Phase 2 (next):** port to React + TypeScript via Vite — data and pure logic with
tests first, then UI, then multitouch input.

## Layout

```
reference/     The original working web app. FROZEN — this is the spec.
               Never edit it. Behaviour, data and styling are all defined here.
native/        Native-only additions (native.css, native.js). Not in reference.
scripts/       install-android-toolchain.sh, sync-www.sh
www/           GENERATED by sync-www.sh. Never edit by hand, never committed.
android/       Generated by `npx cap add android`. A few files are hand-edited
               (see "Hand-edited native files" below).
```

## Commands

| Command | What it does |
|---|---|
| `npm run sync:www` | Rebuild `www/` from `reference/` + `native/` |
| `npm run sync` | The above, then `npx cap sync android` |
| `npm run apk` | Sync, then `./gradlew assembleDebug` |
| `npm run install:apk` | `adb install -r` the debug APK |
| `npm run run:android` | Build + install in one go — the usual loop |
| `npm run logcat` | Tail Capacitor + web console output from the device |

APK lands at `android/app/build/outputs/apk/debug/app-debug.apk`.

The Gradle build needs these in the environment (persisted to `~/.zshrc` by the
install script):

```
JAVA_HOME=/usr/lib/jvm/java-21-openjdk-amd64
ANDROID_HOME=$HOME/Android/Sdk
```

## Driving the device

**Launch through `scripts/device.sh`, never a bare `am start`.** TCL denies the
WebView renderer in the window just after `adb install -r`, and the app then
comes up blank with no crash, no JS error and an empty `document.title`. The
failure is sticky for the life of the process, so the app must be force-stopped
and started again — which is exactly what the helper retries.

Keep the phone unlocked while working. That is not what causes the denial (see
Device notes), but nothing on screen can be verified through a lockscreen and
`input keyevent` will not reach the app.

`scripts/device.sh` handles this so it cannot be forgotten:

| Command | What it does |
|---|---|
| `npm run device:keep-awake` | Stay awake while charging. Do this at the start of a session. |
| `npm run device:launch` | Check awake/unlocked, force-stop, start, wait for the page to actually parse |
| `npm run device:awake` | Just the check — prints a loud warning if locked |
| `npm run device:sleep-normal` | Revert the stay-awake setting when finished |

`device:launch` waits for the page, not merely for the activity: the activity
starts fine even when the renderer was denied. On failure it prints the
`AppBootManager` denial lines rather than leaving a blank window to puzzle over.

It also reads the pid *after* starting the app. `adb install -r` kills the
running process, so a pid captured earlier points at a dead process and the
devtools socket lookup fails while the app itself is healthy — that produced one
false "page never loaded" during Phase 1.

To attach Chrome DevTools by hand: `chrome://inspect`, or
`adb forward tcp:9333 localabstract:webview_devtools_remote_$(adb shell pidof dev.ncode.sp404layers)`
and open `http://127.0.0.1:9333/json`.

## Toolchain (verified, do not bump blind)

Pinned against Capacitor 8.5.2's `capacitor/build.gradle`:
`compileSdk 36`, `targetSdk 36`, `minSdk 24`, Java 21.

- JDK **21** — required by Capacitor 8; `openjdk-21-jdk` from apt
- cmdline-tools **15859902**
- build-tools **36.1.0** — pairs with compileSdk 36
- platforms **android-35**, **android-36**

`sdkmanager` prints a deprecation warning pointing at the newer `android` CLI.
It still works, and it writes the `licenses/` directory that Gradle checks. The
replacement downloads itself on first run and gates on an interactive ToS, which
is worse in an idempotent install script. Revisit if it actually breaks.

## Decisions

**`reference/` is never edited.** It is the Phase 2 spec, so it has to stay
byte-for-byte comparable. Everything native-specific is either an additive file
or one of three removals applied by `sync-www.sh`, which asserts each anchor
exists and fails loudly if the reference ever changes shape.

The three removals:
1. **Service worker registration** — would cache `index.html` and serve a stale
   app after an APK update. Assets are already local, so it buys nothing.
2. **Web manifest link** — the APK's own manifest governs the app.
3. Nothing else. `native.css` and `native.js` are *injected*, not substituted.

**Haptics needs no reference change.** `buzz()` is a `const` and cannot be
reassigned, but it calls `navigator.vibrate`, which can be overridden. `native.js`
redefines that to dispatch to `@capacitor/haptics`: scalar → `impact`, array →
`notification({type:"SUCCESS"})`, `>15` → `notification({type:"ERROR"})`.

**Storage mirrors rather than migrates.** `localStorage` stays the synchronous
source of truth so `load()`/`save()` keep their signatures. `save()` is wrapped
to mirror into `@capacitor/preferences` (SharedPreferences), which survives a
"clear app data" wipe. On boot, if `localStorage` is empty but Preferences is
not, it restores and re-renders. A full async port was rejected as a refactor of
code about to be rewritten in React anyway.

**Back button** is owned by `native.js`: sheet open → close it; otherwise not on
Explore → go to Explore; otherwise exit. Registering a listener suppresses
Capacitor's default history navigation.

**Edge-to-edge is handled natively, not avoided.** Android 16 is API 36 and
Capacitor 8 targets SDK 36, which is exactly the combination where
`windowOptOutEdgeToEdgeEnforcement` stops working. An Android WebView never
populates `env(safe-area-inset-*)`, so `MainActivity` installs an
`OnApplyWindowInsetsListener`, converts px → dp, and pushes the values into
`--ins-t/r/b/l` via `window.__applyInsets()`. `native.css` re-points the
reference's `--sab` at `--ins-b`, so `.bnav` and `.sheet` need no changes.

The push retries on a bounded schedule (25 × 200ms) because insets typically
arrive before the page has run any JS.

**No community plugins.** Only first-party: `@capacitor/core`, `/cli`,
`/android`, `/haptics`, `/preferences`, `/app`.

**Debug signing.** The debug keystore is stable per-machine, so Phase 2's APK
installs over Phase 1's without an uninstall and drill progress survives.
`appId` is `dev.ncode.sp404layers` and must not change for the same reason.

## Phase 2 must carry these UI changes

Phase 1 fixes a strip ergonomics problem in `native/native.{css,js}` rather than
in `reference/`, which stays frozen. The React port must reproduce these, since
they will not come along with the reference:

1. **The two chip rows sit flush on phones.** The reference spaces them with
   `#strip .chips + .chips { margin-top: 6px }`, but the `.lbl` heading between
   them is `display:none` on phones and still in the DOM, so the adjacent-sibling
   selector never matches. Measured gap: 0px. Both selected chips are also
   light-filled and left-aligned, so they visually merge into one shape.
2. **Both chip rows collapse into two pickers side by side on one 44px row.**
   Only one layer is ever active, so neither the mode nor the layer needs a
   scrolling row of its own. Each opens the existing sheet. The mode sheet shows
   `CTXHINT`, which the phone layout otherwise never displays; the layer sheet
   shows each layer's function count.

   This matters for the panel, not just for tidiness: `.pads` uses
   `minmax(34px, 1fr)` rows and on this device it sits exactly at that 34px
   floor, so the SP-404 illustration clips at the bottom if anything takes more
   room. Two rows cost 96px; one costs 44px, and the 52px goes to the panel.

   The layer list is read out of the reference's own chips at render time rather
   than recomputed, so the set, ordering and counts cannot drift from what
   `renderExplore()` decided. In React this becomes shared derived state
   instead.
3. **Chip targets go from 34.9px to 44px.** They scroll horizontally, so an
   undersized target turns a mis-hit into a scroll instead of a tap.
4. **Overflowing rows get a right-edge fade.** Scrollbars are hidden, and both
   rows overflow badly (703px and 952px of content in a 360px viewport) with
   nothing indicating more content. The fade is applied only to rows that
   actually overflow.

In React this should be real component state, not a post-render DOM patch:
Phase 1 has to re-apply the collapse after every `renderExplore()` because that
function rewrites `#strip` wholesale.

## Hand-edited native files

`cap sync` does not regenerate these — keep them when recreating `android/`:

- `android/app/src/main/java/dev/ncode/sp404layers/MainActivity.java` — inset bridge
- `android/app/src/main/AndroidManifest.xml` — `android:screenOrientation="portrait"`

## Device notes (TCL 50 PRO NXTPAPER 5G, Android 16 / API 36)

**adb needs a udev rule.** The phone is USB `1bbb:0c01`. Ubuntu's
`android-sdk-platform-tools-common` matches vendor *and* product, and lists only
older TCL products, so nothing matched and the device node stayed `root:root`.
Fixed with a vendor-wide rule (product IDs change with USB mode):

```
echo 'SUBSYSTEM=="usb", ATTR{idVendor}=="1bbb", MODE="0660", GROUP="plugdev", TAG+="uaccess"' \
  | sudo tee /etc/udev/rules.d/51-android-tcl.rules
sudo udevadm control --reload-rules && sudo udevadm trigger
```

It lives in `/etc/udev` so apt upgrades don't overwrite it. The `uaccess` tag
grants the logged-in session access, so no logout is needed.

**A blank grey window means the renderer was denied — relaunch.** TCL's
`AppBootManagerService` sometimes refuses to let the app bind the WebView's
sandboxed renderer process:

```
W/AppBootManager: Type[TYPE_SERVICE];Result[false];
  Target[org.chromium.content.app.SandboxedProcessService0];
  Caller[dev.ncode.sp404layers];Reason[screen_on & caller care]
E/cr_ChildProcessConn: Failed to establish the service connection.
```

With no renderer the page never parses, so there is no crash, no JS error, an
empty `document.title`, and DevTools `Runtime.evaluate` hangs. The failure is
sticky for the life of the process — reopening from Recents keeps the grey
window. Only `am force-stop` plus a fresh start clears it.

**The trigger is the window just after `adb install -r` replaces the package.**
Every observed failure followed an install; an immediate relaunch with no
install has always succeeded on the first try. Do not trust the `Reason` string:
it reports the current screen state, and both `screen_off` and `screen_on` have
been seen denying, so screen state is not the cause. An earlier version of this
file claimed it was — that was wrong.

`scripts/device.sh launch` therefore retries the whole force-stop/start cycle up
to 3 times. This is an OEM policy, not an app bug, and it only bites when
launching over adb — tapping the icon is fine.

## Gotchas

- The reference's multitouch relies on `touch-action:none` on `.unit` plus
  per-`pointerId` tracking in a `Map`. This is the most delicate part to port in
  Phase 2 — read `exDown`/`exUp`/`drDown`/`drUp` before touching it.
- `store`, `st` and `SK` are `const`/`let` at classic-script top level: reachable
  by bare name from `native.js`, but absent from `window`. `save`/`render`/
  `closeSheet` are function declarations, so they *are* on `window` and can be
  wrapped.