questshock/AGENTS.md

# AGENTS.md

Guidance for AI coding agents (and new contributors) working on Questshock.
README.md is the user-facing build/usage guide and CONFIG.md documents the
configuration file; this file covers how the code is organised and the rules to
follow when changing it.

## 1. What this project is

Questshock plays the 1994 game System Shock on a standalone VR headset (Meta
Quest 2 is the tested device). It wraps [Shockolate](https://github.com/Interrupt/systemshock),
a cross-platform port of the original engine, in an Android app that:

- runs the unmodified 2D engine (software or OpenGL renderer) and shows its
  frame on a head-tracked virtual screen (an OpenXR quad layer);
- shows a menu and an on-screen keyboard as separate OpenXR quads, operated by
  a laser pointer from either controller;
- maps controller inputs to game actions through a configurable binding layer;
- persists settings in `/sdcard/questshock/questshock.config.json`.

A desktop (Linux/Windows) build of the same engine exists for development
without a headset; it has none of the Android/OpenXR code.

## 2. Hard rules

These come from the maintainer. Follow them without being asked again.

1. **Never commit.** Do not run `git commit` (or amend, rebase, push), even if
   asked to commit. Draft the commit message and show it; the maintainer runs
   the commit. Mention any new untracked file that has to be `git add`ed
   (typically a new patch under `android/engine-patches/`).
2. **Do not build.** Do not run `make apk`, `./gradlew`, or `make android-studio`
   to check that a change compiles. The maintainer deploys from Android Studio.
   `make apk` and `make android-studio` overwrite `android/engine.properties`
   with container-only paths and break an open Android Studio project. What you
   can do is dry-run patches (section 6) and run static consistency checks
   (section 12). Say plainly in your report that the change was not built or
   tested.
3. **`engine/` and `android/gl4es-src/` are never edited.** They are vendored
   snapshots. Every change to them is a numbered patch under
   `android/engine-patches/` or `android/gl4es-patches/`, applied to a scratch
   copy at build time. (`engine/` is GPLv3, see README section 6.)
4. **Patch numbers stay contiguous** (`01`, `02`, ... with no gap). When you
   insert or delete a patch, renumber the rest and update every reference to
   the numbers (README patch reference, code comments).
5. **Comments and documentation describe the current state and why it has to be
   that way.** No history or narrative: no "used to", "originally", "no
   longer", "now", "this was fixed", "confirmed on device", incident stories or
   dropped alternatives. History belongs in commit messages. A comment that
   would read oddly to someone who never saw an earlier version should be
   rewritten or cut. Default to one or two lines. (README section 5.5, the
   debugging notes, is the one deliberate exception.)
6. **Standalone headset only, OpenXR first.** No feature may need a host PC
   (no PCVR, tethering or streaming). Prefer OpenXR APIs over vendor-specific
   ones (Meta's Oculus Mobile SDK and the like) so the port can run on other
   Android OpenXR headsets. Flag a request that would break either rule
   instead of quietly doing it.
7. **Do not bump `build-image/VERSION`** just because `build-image/Dockerfile`
   changed. Bump it only once a build with the current number has succeeded
   end to end (for example a CI run). Ask if unsure.
8. **Keep docs in sync with behaviour.** A user-visible change updates
   README.md and/or CONFIG.md in the same change; a new or renumbered engine
   patch updates the README patch reference (section 5.4).

## 3. Repository layout

| Path | What it is |
|---|---|
| `engine/` | Vendored Shockolate source. Read-only for us. |
| `android/engine-patches/` | Numbered `patch -p1` files applied to a scratch copy of `engine/`. |
| `android/gl4es-src/`, `android/gl4es-patches/` | Vendored GL4ES (desktop GL to GLES) and its patches. |
| `android/app/src/main/cpp/` | First-party native code (section 4). |
| `android/app/src/main/java/de/ladkau/questshock/` | First-party Java (section 4). `org/libsdl/app/` is vendored SDL2 glue (zlib). |
| `android/app/build.gradle` | Gradle project; the `stageEngine` task stages the patched engine. |
| `android/force-rebuild.sh` | Stops Gradle daemons and wipes staged/build output for a fully fresh native build. |
| `build-image/` | Docker build environment (`Dockerfile`, `VERSION`, `prepare-android-project.sh`, `build-apk.sh`, engine build scripts). |
| `res/` | Bundled resources: `questshock.config.default.json`, `controller_profiles/` (JSON + PNG per controller), `assets/` (where the user's own game data goes, git-ignored), `run.sh`/`run.bat`. |
| `Makefile` | `engine`, `dist`, `package`, `apk`, `android-studio`, `clean`, ... (see README section 2). |
| `README.md`, `CONFIG.md`, `NOTICE.txt` | User docs, config reference, license notice. |

`build/`, `dist/`, `dist-win/` and `res/assets/ss_ee/` are generated or
proprietary and git-ignored. `registry.env` holds local registry settings; do
not print it or commit it.

## 4. Android app architecture

### 4.1 Native modules (`android/app/src/main/cpp/`)

| File | Role |
|---|---|
| `xr_session.c/.h` | OpenXR instance and session lifecycle, frame loop, composition layers (game quad, menu, keyboard, laser beams). |
| `xr_swapchain.c/.h` | Swapchain creation, acquire and release, per-image FBOs. |
| `xr_overlay.c/.h` | Generic "off-screen Android `View` rendered into an OpenXR quad" module, hit-tested by a laser pointer. The menu and the keyboard are two instances. |
| `xr_input.c/.h` | Controller input: OpenXR actions, raw-input layer, action bindings, capture-mode rebinding, key injection into the engine, free view, cyberspace scaling, snap-turn/smooth-move of the player's position, pointer rays. The largest file. |
| `xr_mouse.c/.h` | Injects mouse motion and clicks into the engine. |
| `qs_config.c/.h` | Configuration: JSON parse, apply, write; screen profiles; menu-driven requests; cheats; menu-triggered pause. |
| `questshock_native.c` | JNI exports and small native helpers (`nativeChdir`, `nativeSendPrintableChar`, ...). |

### 4.2 Java classes

| Class | Role |
|---|---|
| `QuestShockActivity` | `SDLActivity` subclass. Creates `/sdcard/questshock/`, extracts bundled files, blocks engine start until the game data exists. |
| `OverlayPanel` | Base for the off-screen panels: builds the view tree, renders it to a texture, turns ray hits into touch events. |
| `MenuOverlay` | The menu: Main Menu, Video Options, Controller Options and Cheats tabs. Singleton. |
| `KeyboardOverlay` | The on-screen keyboard. |
| `Strings` | All menu and keyboard text in English, French and German. |

### 4.3 How the pieces fit

- The engine's present path is redirected (engine patch 11) so that
  `SDLDraw()` submits into the OpenXR game-quad swapchain. The per-frame
  entry point of `xr_input.c` is `xr_input_sync_and_draw()`, called from the
  frame path in `xr_session.c` on the engine's own thread.
- The engine's own log output goes to logcat (patch 08); Java and native
  first-party code log under the tag `QuestShock`.
- Bindings, config and menu state are owned natively. Java only displays and
  requests.

### 4.4 Threads and cross-thread requests

- Engine state (player struct, game loop, cheats, config apply) must only be
  touched on the engine thread.
- Menu code calls native functions through JNI. Anything that changes engine
  state must be enqueued, not executed inline: the JNI export calls a
  `qs_config_request_*()` function, which pushes an SDL custom event
  (`SDL_RegisterEvents`); `qs_config_handle_event()` handles it on the engine
  thread (it is called from `pump_events()`, engine patch 21). To add a new
  request, add an event type, the `qs_config_request_*()` enqueue function and
  a branch in `qs_config_handle_event()`.
- Getters that Java calls (`qs_config_cheat_unlimited_mask()`, binding-name
  getters, ...) must be plain scalar or string reads that are safe from any
  thread.
- Per-frame work that must run on the engine thread (such as
  `qs_config_frame_tick()`) is called from `xr_input.c`.
- JNI symbol names must match the Java `native` declarations exactly
  (`Java_de_ladkau_questshock_<Class>_<method>`). A mismatch only fails at
  runtime, so check it (section 12).

### 4.5 Off-screen views (`OverlayPanel`, `MenuOverlay`, `KeyboardOverlay`)

The view tree is built and drawn from native code and is never attached to a
window. Consequences that shape the UI code:

- Only `ACTION_DOWN`/`ACTION_UP` touches arrive (the laser trigger). There is no
  drag, fling or multi-touch. Scrolling is done by a self-drawn scroll bar
  (`ScrollBarView` in `MenuOverlay`), not by the framework.
- `View.post()` never runs, so anything that defers work through it does not
  work. `ProgressBar` and `SeekBar` are unusable for the same reason.
- Hover and hit-testing use `OverlayPanel.absoluteBounds()`, which subtracts
  ancestor scroll offsets.
- Toggling a child's visibility needs an explicit re-measure and re-layout
  (see `relayoutAndRedraw()`).
- All user-visible text goes through `Strings.get(key, language)` with an
  English, French and German entry, and is re-applied in `applyTranslations()`
  when the language changes. "OpenGL" is a brand name and is not translated.

## 5. Configuration system

- `qs_config.c` holds one parsed struct per group (`video_options`, `general`,
  `player_position`, `player_controls`), a parse function, an apply function,
  and the writer `qs_config_write_file()`. Groups are tagged live-appliable or
  restart-required (`QS_*_REQUIRES_RESTART`).
- Load order at startup: `questshock.config.json`, else
  `questshock.config.default.json` (bundled, refreshed on every launch), else
  the engine's own `prefs.txt` behaviour. Save is only ever an explicit menu
  action.
- Invalid values are logged and skipped individually; unknown keys are ignored.

**Adding an option:** parsed-struct field, parse, apply (with validation and a
`WARN` on invalid input), write in `qs_config_write_file()`, restart flag,
`CONFIG.md`, and (if it should have a shipped default) `res/questshock.config.default.json`.

The virtual screen has two profiles, "initial" (splash, cutscenes, main menu)
and "game", switched by `qs_screen_profile_notify_loop_mode()` from engine
patch 22. `s_screen_profile_is_game` in `qs_config.c` doubles as "a game is
running" and gates the cheats and the menu pause.

## 6. Engine patches

Rules:

- Guard every engine change with `#ifdef __ANDROID__` so the desktop build is
  unaffected, and keep hunks minimal.
- Patches are applied in filename order with `patch -p1` from the engine root
  (paths look like `a/src/GameSrc/hkeyfunc.c`). Patch N is generated against
  the tree with patches `01..N-1` applied.
- Some engine files use CRLF line endings (for example `mouselook.c`). Edits
  and generated patches must preserve them byte for byte; check with `file`
  or `cat -A`. An editor or script that rewrites line endings produces a
  whole-file diff.
- Do not hand-edit hunk headers. Regenerate the patch from a scratch copy.

Creating or changing a patch:

1. Make a scratch copy of `engine/` (for example under the session scratch
   directory) and apply patches `01..N-1` to it (`patch -p1 -d <scratch> < ...`).
2. Copy the target file(s) to a second location, edit them in the scratch copy.
3. Produce the patch with `diff -u` using `a/` and `b/` path prefixes relative
   to the engine root, and save it as `android/engine-patches/NN-android-<topic>.patch`.
4. Dry-run the whole series on a fresh copy of `engine/`
   (`patch -p1 --dry-run`, or apply for real on the copy) and confirm every
   patch applies cleanly, with the patched file byte-identical to what you
   edited.
5. Keep numbering contiguous, and update the README patch reference (5.4) and
   any code comments that cite patch numbers.

Gradle's `stageEngine` task re-stages and re-patches on build, but it can wrongly
report `UP-TO-DATE` when a **new** patch file appears. If a native change does
not show up on the device, tell the maintainer to run `./gradlew --stop`, or
`android/force-rebuild.sh`, or delete `build/android-engine`, before assuming
the change is wrong.

Engine symbols used from first-party code (for example `game_paused`,
`pause_game_func`, `toggle_giveall_func`, `qs_cheat_refill`,
`qs_in_cyberspace`) are declared `extern` next to their use in `qs_config.c` or
`xr_input.c`, with a comment naming the engine file and patch.

## 7. Controller mapping (`xr_input.c`)

Structure:

- Physical controls are OpenXR actions, suggested once against three
  interaction profiles: Meta Touch, HTC Vive wand and the core
  `khr/simple_controller`. A single wrong path makes the whole
  `xrSuggestInteractionProfileBindings` call fail, so each profile lists only
  components it really has. A failure calls
  `qs_config_report_fatal_input_error()` and aborts input init.
- The **raw-input layer** (`QsRawInput`) digitizes every physical control
  (buttons, triggers, squeezes, thumbstick clicks, and eight thumbstick
  directions with hysteresis) each frame. `QS_RAW_NONE` means unbound.
- **Actions** (`QsControlAction`) are bound to raw inputs through `s_binding[]`.
  The default bindings are `kDefaults[]`.
- Contexts: `ALWAYS`, `NORMAL` (move, strafe, turn, jump, stand, crouch, prone)
  and `CYBER` (the eleven `cyber_*` actions). The active set is chosen with
  `qs_in_cyberspace()` (patch 24). Two actions conflict only if their contexts
  can be active together (`xr_input_contexts_overlap()`).
- Capture mode (`xr_input_process_capture()`): the next fresh raw down-edge is
  assigned to the chosen action. Any other action in an overlapping context that
  held that input (or its symmetric alias) is set to `none`. The reset and the
  timeout (8 s) paths never leave a half-assigned state.
- The menu button is not a raw input and can never be bound, so the menu can
  always be reached to press **Reset to Defaults**.
- While the menu is open, `mouse_click` is always the trigger (the controller
  used to operate the menu); after it closes, the bound `mouse_click` drives
  both the keyboard and the game quad.
- While the Controller Options tab is open, the menu's own thumbstick
  snap-turn and smooth-move are disabled
  (`g_controller_options_tab_open`, set through
  `nativeSetControllerOptionsTabOpen`).
- Free view: holding a `free_*_thumbstick_view` binding turns that stick into
  the engine's mouse look (cursor forced hidden, stick direction bindings
  suspended). It uses `SDL_ShowCursor(SDL_DISABLE)` because the engine zeroes
  mouse-look velocity while the cursor is visible.
- Cyberspace pitch and bank scale with stick deflection through the globals
  from patch 25 (`qs_cyber_pitch_scale`, `qs_cyber_bank_scale`).

### Adding or changing a bindable action (checklist)

All of these lists share one order and must stay identical:

1. `QsControlAction` enum in `xr_input.c` (and append before `QS_ACTION_COUNT`).
2. `kActionNames[]` in `xr_input.c`.
3. `s_binding[]` initial values and `kDefaults[]` in `xr_input.c`.
4. If it injects a key: a `kKeyActions[]` entry (keycode, modifiers, whether it
   needs `SDL_TEXTINPUT`); add the key to the stuck-key watchdog list
   (`kWatchedKeys`) if it is held continuously.
5. `ACTION_KEYS` in `MenuOverlay.java`, and `FIRST_ROW_ACTIONS` if it should be
   listed first.
6. `Strings.java`: `action_<key>` in EN/FR/DE.
7. `QS_MAX_PLAYER_CONTROL_ACTIONS` in `qs_config.c` if the count outgrows it.
8. `CONFIG.md`: the action tables and the count in the Player Controls intro;
   README default-controls table if it has a default binding.
9. Check that no two actions that can be active together share a default input.

### Injecting keys into the engine

- Plain printable keys (letters, digits, Space, punctuation) need an
  `SDL_TEXTINPUT` event plus `SDL_KEYDOWN`/`SDL_KEYUP`. Modifier, control-range,
  F and keypad keys use `SDL_KEYDOWN`/`SDL_KEYUP` with the right `mod`.
- **Send the release on the real up edge, never in the same call as the
  press.** The engine polls movement keys once per frame before it drains
  events, so a press and release drained together are never seen and the key
  silently does nothing. Tie the release to the physical button's up edge (or
  the touch's `ACTION_UP`/`ACTION_CANCEL`).
- Held keys are tracked in the engine's `sshockKeyStates[]`; `xr_input.c`
  keeps a watchdog that clears a watched key the engine still thinks is down
  after its binding is released.
- Actions that share an engine key (for example the several ways to fire, or
  the movement keys) are handled with sibling logic in the dispatch loop
  (`wantDown[]`); do not press or release the shared key independently.

## 8. Cheats tab

- Buttons and switches live in `MenuOverlay.buildCheatsTab()`; ids are
  `QS_CHEAT_*` in `qs_config.c` and `CHEAT_*` in `MenuOverlay.java` (keep them
  identical).
- The engine's own cheat handlers (`toggle_giveall_func`, `toggle_physics_func`,
  `toggle_up_level_func`, `toggle_down_level_func`) are called on the engine
  thread through `qs_apply_cheat()`, and only while a game is running.
- The four unlimited switches are a bitmask in `qs_config.c`
  (`QS_CHEAT_MASK_*`: health 1, energy 2, ammo 4, items 8). Every frame
  `qs_config_frame_tick()` calls `qs_cheat_refill(mask)` (patch 26). The mask
  values must match the patch. The switches are not persisted.
- The four `cheat_*` hotkeys are deliberately not bindable in
  `player_controls`. New cheats go on the Cheats tab.

## 9. Menu pause

Opening the menu pauses a running game (`qs_apply_menu_pause()` through the
menu-visibility event); closing it resumes only if the menu did the pausing and
the game is still paused. Do not toggle pause blindly, since the pause function
toggles.

## 10. Bundled files on the device

`QuestShockActivity` extracts these into `/sdcard/questshock/`:

- shaders, the default soundfont and `GET_ASSETS_QUEST.txt` (once);
- `questshock.config.default.json` and `controller_profiles/` (every launch,
  overwriting only the bundled filenames so user-added profiles survive).

`res/controller_profiles/` and the default config are staged into APK assets by
`build-image/prepare-android-project.sh`; new staged directories must also be
declared as `inputs.dir(...)` of `stageEngine` in `android/app/build.gradle`.

The proprietary game data (`res/data/`, `res/sound/`) is never bundled or
committed. The app refuses to start the engine until it is present.

## 11. Code and documentation style

- Match the surrounding code: naming, comment density, idiom. C is plain C with
  `static` helpers and `//` comments; Java targets Android API 34 and uses only the SDK plus
  `androidx.core`.
- Keep functions and file-level constants near their use. Put magic numbers in
  named constants (see `QS_FREE_VIEW_*`, `QS_CYBER_ROTATION_*`).
- Keep the `xr_input.h` and `qs_config.h` declarations documented with a short
  comment saying which thread may call them.
- Comments: what and why, current state only (rule 5 in section 2).
- Docs: README.md is organised by numbered sections that other text cites
  ("5.5.3"); do not renumber existing sections. Add new material as a new
  subsection instead.
- English, French and German strings live in `Strings.java`; keep the three
  entries of each key on the same `put(...)`.

## 12. Verifying a change without building

Because you may not build (rule 2), check statically and say so in the report:

- **Patches:** apply the whole series to a fresh copy of `engine/` and confirm
  no rejects. Confirm the edited file matches the patched result byte for byte.
- **JNI:** every `native` method in the Java classes has a
  `Java_de_ladkau_questshock_<Class>_<method>` export with a matching signature,
  and no export is left without a Java declaration.
- **Ordered lists:** `QsControlAction`, `kActionNames[]`, `s_binding[]`,
  `kDefaults[]` and `ACTION_KEYS` have the same length and order.
- **Strings:** every `Strings.get("...")` key exists in `Strings.java`.
- **Balance:** braces and parentheses balance. `qs_config.c` reports a
  brace-count offset of +5 from character literals containing `'{'`; that is
  not a bug.
- **Docs:** README and CONFIG.md agree with the code (action counts, default
  bindings, patch list).

Then report what was checked, what was not (build, on-device behaviour), and
any device check the maintainer should do (for example a new patch that may
need `android/force-rebuild.sh`).

## 13. Commit messages

Draft only (rule 1). Use a short imperative subject (about 70 characters), a
blank line, then a body that explains what the change does and why: the
user-visible behaviour, the mechanism, and any constraint worth remembering.
Mention new files that need `git add`.