xtc/README.md

# xtc — a lightweight, modular DAW

`xtc` is a new, energyXT-inspired digital audio workstation project. It is not a clone and contains no energyXT source code or assets.

## Design decisions

- **Modular engine first:** sequencer, instruments, effects, mixers and I/O are nodes in one processing graph.
- **C core:** project model, graph, DSP and audio engine are implemented in C.
- **FLTK/C++ GUI:** C++ is confined to the graphical interface and calls the core through a C API.
- **Linux first:** keep backend-specific details behind an interface.
- **Small increments:** build and test each milestone before adding features.

## Current status

This repository is a starter scaffold, not a production DAW. It currently provides:
- a small C library/API;
- a mono graph model with port validation, cycle rejection and topological ordering;
- compiled offline plans with preallocated buffers, sine oscillator, audio source, gain, meter and output nodes;
- C tests for deterministic rendering, routing, validation and lifecycle;
- an optional JACK-compatible backend with mono input and mono/stereo output with start/stop, routing and status;
- safe control/audio plan handoff and concurrent replacement tests;
- an optional FLTK shell with engine controls, view switching and backend status;
- a modular graph editor with transactional edits and live plan adoption status;
- versioned project save/load and a timeline for tracks and clips;
- sample-counted transport, selection, move/trim, timeline zoom and scrolling;
- WAV import/graph playback, bounded recording and missing-asset relinking;
- MIDI clips, a sine instrument, JACK MIDI input and a basic piano roll;
- stereo track/bus gain/pan/mute/solo, dBFS peak meters and gain/pan automation lanes;
- bounded undo/redo with keyboard shortcuts;
- configurable boundary fades, gain ramps and graceful GUI playback transitions;
- native C processors, deterministic source packaging and staged install/uninstall;
- architecture, format, GUI, roadmap, and decision documents.

The JACK backend has passed software-loopback testing; physical-device playback
and capture are unverified. MIDI recording remains deferred. Bounded LADSPA
hosting supports the compatible mono processors documented in
[PLUGIN_HOSTING.md](docs/PLUGIN_HOSTING.md).

## Build

Requirements: a C compiler, a C++ compiler, GNU Make, and `pkg-config`. FLTK is optional for the core and tests.

```sh
make
make test
```

`make` also builds `build/xtc-check`, a headless core startup/shutdown
check. Use `make debug` for a separate debug build and test run. See
[docs/BUILD.md](docs/BUILD.md) for the inspected toolchain and baseline limits.

Build the optional FLTK GUI if FLTK is installed:

```sh
make gui
```

Run the GUI:

```sh
./build/xtc
```

See [the minimal music-making workflow](docs/WORKFLOW.md) for creating, saving,
reopening and playing a project.

The GUI opens JACK and offers Play/Pause/Stop/To start/Reconnect, backend status and view
switching. The initial empty graph is silent. Modular Graph supports adding,
moving and deleting oscillator/audio/instrument/gain/meter/output nodes and connecting ports.
Import WAV (Ctrl+I) creates playable clips; Add region creates silent placeholders.
Record captures JACK input to a chosen WAV; Stop finalizes and adds the take.
Save the project after recording. External asset paths must remain available;
select a missing clip and use File/Relink selected audio to repair it.
Add MIDI clip on an existing track, then open Piano roll (Ctrl+4) to draw notes.
Connect a MIDI source to the JACK `midi_in` port for live playing; Panic/F9
silences held notes. See [MIDI workflow and limits](docs/MIDI.md).
See [audio workflow and limits](docs/AUDIO_FILES.md).
Mixer (Ctrl+2) selects a track for gain/pan/mute/solo and automation editing.
Ctrl+Z undoes; Ctrl+Shift+Z or Ctrl+Y redoes up to 32 edits.
The GUI now exposes left `output` and `output_right` JACK ports; route both
explicitly for stereo. See [mixer workflow and limits](docs/MIXER.md).
Use Add track/Add region, drag regions or their edges, and Zoom +/-; scrollbars pan.
Ctrl+N/O/S creates, opens or saves a project; Save As chooses another path.
Arrangement edits stop playback; graph edits remain live.
The ruler seeks while stopped. Stop pauses; Reconnect and project load reset position. F5 starts, F8 stops, Space toggles, F6 reconnects, and Ctrl+1/2/3
switches views. Ctrl+Q closes the client and window. No physical ports are
connected automatically. In Modular Graph, drag output to input to connect;
select a node or wire and press Delete to remove it. Invalid edits leave the
active graph intact; queued changes are labeled until the engine adopts them.
See [GUI documentation](docs/GUI.md).
For Linux installation, routing and CLI options see [LINUX.md](docs/LINUX.md);
for native effects/instruments see [NATIVE_API.md](docs/NATIVE_API.md).
`make release`, `make dist`, `make test-install` and `make test-release` provide
release preparation; see [RELEASING.md](docs/RELEASING.md) for exact guarantees.
With JACK development files and an existing JACK-compatible server, run the
isolated software-loopback test with `make test-jack` and the record/reopen/play
acceptance test with `make test-jack-audio` and MIDI acceptance with
`make test-jack-midi`. It connects only test
clients. See [engine documentation](docs/AUDIO_ENGINE.md) for configuration,
routing, ownership and recovery.

Clean generated files:

```sh
make clean
```

## Suggested first agent task

Read `AGENT.md` and `docs/ARCHITECTURE.md`. Inspect the existing implementation, run `make test`, and report gaps before adding the next feature. Do not jump directly to plugin hosting or a full sequencer.

## License

The project is scaffolded under the MIT License; see `LICENSE`. Review the licenses of any future dependencies before distribution.

Audio timing, transitions, latency limits and listening previews are described
in [docs/AUDIO_QUALITY.md](docs/AUDIO_QUALITY.md). Human listening acceptance
for the Phase 12 transitions remains pending.

Phases 13–15 add no-clobber recording/recovery, parameterized native C processors,
and trusted in-process LADSPA hosting with persisted identity/control values.
See [RECOVERY.md](docs/RECOVERY.md), [NATIVE_API.md](docs/NATIVE_API.md) and
[PLUGIN_HOSTING.md](docs/PLUGIN_HOSTING.md) for commands and limits.

For everyday use see [USER_MANUAL.md](docs/USER_MANUAL.md),
[KNOWN_LIMITATIONS.md](docs/KNOWN_LIMITATIONS.md) and
[MAINTENANCE.md](docs/MAINTENANCE.md). `xtc-check --diagnose` reports build features;
`make test-package` checks a local system-linked Linux binary archive.
Phases 16–20 add effect automation/controllers, editing commands, v7 project-folder
media paths, performance baselines and release/installation checks.

Phase 22 adds non-destructive audio splitting, clip gain/fades and cached timeline
waveforms, with undo and v8 persistence (reading v1–v7). See
[AUDIO_FILES.md](docs/AUDIO_FILES.md#phase-22-non-destructive-clip-editing).
`make test-audio-editing` checks source preservation and exact boundary output.
Time stretching and independent pitch shifting remain deferred.

Phase 23 adds signal-flow graph layout, routing diagnostics, direction/role
indicators and atomic unity-gain insertion into a wire. See
[ROUTING.md](docs/ROUTING.md); `make test-routing` verifies the C routing contract.

Phase 24 adds one-level mix buses, routing, coherent track/bus peaks and master
clipping indicators, persisted in v9 (reading v1–v8). See [MIXER.md](docs/MIXER.md).

Phase 25 adds LADSPA descriptor browsing, an identity/parameter editor with
reset, transactional replacement and insertion into graph wires. See
[PLUGIN_HOSTING.md](docs/PLUGIN_HOSTING.md) for compatibility and lifecycle limits.

Phase 26 adds common parameter targets, Linear/Hold mixer automation and saved
per-channel live MIDI CC bindings. Project v10 reads v1–v9. See
[CONTROL.md](docs/CONTROL.md) for timing, precedence and qualification limits.

Phase 27 reserves undo storage before edits/publication, groups completed takes,
preserves surviving editor selections and improves context menus/focus feedback.
See [EDITING.md](docs/EDITING.md) for the workflow audit and failure boundaries.

Project troubleshooting: `xtc-check --validate PROJECT.xtc` reports metadata
errors with the expected record and syntax line. `xtc-check --inspect PROJECT.xtc`
lists resolved media/module paths and plugin identities without executing plugins
or starting JACK. Exit codes: 0 = valid metadata and available files, 2 = missing
or unreadable references, 1 = metadata/I/O error. File availability does not
certify WAV contents or plugin compatibility. See [PROJECT_FORMAT.md](docs/PROJECT_FORMAT.md)
for the compatibility and relocation policy.