midigrid/README.md

# MIDI Grid — accessible quick MIDI entry for REAPER

A grid / step-sequencer entry mode for REAPER's MIDI editor, built for
keyboard-and-speech use with [OSARA](https://osara.reaperaccessibility.com/).

Left and right walk the timeline one grid cell at a time. Up and down walk the
pitch axis **by scale degree**. Enter toggles a note in the current cell.
Everything you land on is spoken and sounded, so you can hear what is already
there as you move.

It is **not** a replacement for the MIDI editor. It is a fast way to block out
a clip; switch grid mode off and OSARA's normal editing is right there,
unchanged, on the same cursor.

## Requirements

- REAPER
- **OSARA** — for speech output
- **SWS** — for the note-naming octave preference

No other extensions. No ReaPack, no js_ReaScriptAPI, no ReaImGui.

## Install

Clone or download this repository anywhere you like, then:

1. **Close REAPER completely.** It rewrites `reaper-kb.ini` when it exits and
   will throw away anything written while it is running.
2. Run:

   ```powershell
   powershell -ExecutionPolicy Bypass -File install.ps1
   ```

3. Start REAPER, select a MIDI item, press **`Alt+Shift+G`**.

You should hear something like *"Grid mode on, C major, grid 1/16, hold off,
C5, 1.1.00"*.

To remove it again: `powershell -ExecutionPolicy Bypass -File install.ps1 -Uninstall`

The installer backs up `reaper-kb.ini` to `reaper-kb.ini.midigrid-backup`
before its first change, and is safe to re-run.

### Why not "Import key map"?

`MidiGrid.ReaperKeyMap` is included for reference, but **importing it does not
reliably work**, and the way it fails is silent and confusing: REAPER accepts
the file, registers the script actions, and then converts every key binding it
cannot resolve into a `No-op (no action)` entry. The keys appear bound in the
action list but do nothing.

The cause is that a `KEY` line must reference the *named command* — the `SCR`
id with a **leading underscore** (`_RSmidigrid_open`), not the bare id
(`RSmidigrid_open`). `install.ps1` writes the underscored form directly.

If you would rather not run a script, you can bind the ten `MIDI Grid:`
actions by hand in Actions → Show action list. That always works.

## Keys

**Main section**

| Key | Action |
|---|---|
| `Alt+Shift+G` | Open selected item in grid mode |

**MIDI editor section**

| Key | Grid mode ON | Grid mode OFF (passes through to) |
|---|---|---|
| `Left` / `Right` | Cursor back / forward one grid cell | OSARA previous / next chord |
| `Up` / `Down` | Pitch up / down one scale degree | OSARA higher / lower note in chord |
| `Enter` | Toggle note at cursor cell | Edit: Event properties |
| `L` / `Shift+L` | Lengthen / shorten note by one cell | Edit: Lengthen / shorten notes one grid unit |
| `Alt+J` | Join a run of repeated notes into one | — |
| `Alt+3` | Toggle diatonic triad on cursor pitch | — |
| `Alt+7` | Toggle diatonic seventh chord | — |
| `Alt+Shift+Up` / `Alt+Shift+Down` | Velocity up / down | — |
| `Alt+G` | **Toggle grid mode on/off** | — |
| `Alt+H` | Toggle hold mode | — |
| `Alt+A` | Repeat current cell (speak + sound) | — |
| `Alt+S` | Set root and scale | — |
| `1`–`9` | Grid size — REAPER's own grid actions | same |

`Alt+Shift+G` **opens** grid mode; it does not close it. Use `Alt+G` inside
the editor to toggle back off.

## How it integrates

- **Grid size is REAPER's grid.** Read via `MIDI_GetGrid()`, so whatever you
  already have bound to the MIDI editor's grid actions (by default `1` = 1/1,
  `2` = 1/2, `4` = 1/4, `6` = 1/16, `8` = 1/8, `3` = 1/32) drives this too.
  Nothing new to learn.
- **The cursor is REAPER's cursor.** Time is the native edit cursor; pitch is
  the MIDI editor's `active_note_row`. No private cursor state exists, so grid
  mode and OSARA cannot drift out of sync — you can switch between them
  mid-phrase.
- **Turning grid mode off restores everything.** Each bound key forwards to
  what it did before, so nothing is permanently taken away.

## What gets spoken

- **Left / right** — cell position and everything sounding in it:
  `"3.2.00, C5, E5"`, and those notes are sounded together.
- **Up / down** — the note name, plus `"on"` if this cell already holds that
  pitch: `"E5, on"`.
- **Enter** — `"E5 on, added"` or `"E5 off, removed"`.

## Hold mode

With hold **off**, toggling adjacent cells at the same pitch gives separate
repeated notes.

With hold **on**, a new note touching an existing note of the same pitch joins
it into one sustained note. Toggling a cell off in the middle of a sustained
run splits it in two; at either end, it shortens it. So you can draw a long
note by arrowing right and pressing Enter across several cells.

Hold mode governs **entry only** — it never retroactively merges notes that
are already there. To sustain what you have already written, use the length
keys below.

## Note length — sustaining notes you already entered

- **`L`** — lengthen the note under the cursor by one grid cell.
- **`Shift+L`** — shorten it by one cell. It never shrinks below a single
  cell; it says *"minimum"* rather than deleting the note.
- **`Alt+J`** — fuse an entire run of repeated notes at this pitch into one
  sustained note, in a single keystroke.

Lengthening **swallows** any same-pitch note it runs into, taking that note's
tail if it reached further. So pressing `L` across a row of repeated notes
fuses them rather than producing overlaps.

Each press reports the resulting length — *"E5, 3 cells"*, or *"E5, 2 cells,
joined 1"* when it absorbed something.

### Why not re-toggle with hold on instead?

Turning hold on and re-entering existing notes does work. But toggling a note
off and on **deletes and recreates it, resetting its velocity to the default**
— if you have shaped dynamics, that quietly discards them.

The length keys edit the note in place, so velocity, channel and note identity
survive. They also need no mode: `L` behaves identically whether hold is on or
off, so there is no state to set up beforehand and none to remember to turn
off afterwards.

## Chords

`Alt+3` stamps a **diatonic triad** on the cursor pitch; `Alt+7` a seventh
chord. Both are built by stacking scale thirds, so the quality follows the
degree automatically — in C major, `Alt+3` on C gives C major, on D gives D
minor, on B gives B diminished. There is no chord-quality table to configure
and no way to land on a chord outside the key.

If every tone of the chord is already in the cell, the keystroke removes them
all; otherwise it fills in whatever is missing. Chord tones obey hold mode,
splitting and trimming exactly like single notes.

You can also build chords by hand at any time — arrow to a pitch, press Enter,
arrow to another, press Enter. The cursor never moves horizontally when you
toggle, so stacking notes in one cell has always worked. `Alt+3` and `Alt+7`
are just the one-keystroke version.

In the chromatic scale, "stacking thirds" degenerates into stacked whole
tones. Predictable, but not musically useful — pick a real scale first.

## Velocity

`Alt+Shift+Up` and `Alt+Shift+Down` change velocity in steps of 8.

The key does one of two things depending on where you are, and says which:

- **On a note** — changes that note's velocity: *"E5 velocity 104"*, and
  replays it at the new level so you can hear the change.
- **On an empty cell** — changes the default for newly inserted notes:
  *"Default velocity 104"*.

So you can set a level and then draw at it, or draw first and shape the
dynamics afterwards, without a mode switch either way.

Set `velstep` in `ExtState` if steps of 8 are too coarse or too fine.

## Scales

`Alt+S` prompts for a root (`C`, `F#`, `Bb`…) and a scale number. Up and down
then move by scale degree, which is what makes entry fast — you cannot land on
a wrong note by accident. Pick `chromatic` for plain semitone movement.

If the cursor sits on a note outside the current scale, up/down move to the
nearest scale tone in that direction rather than getting stuck.

## Architecture notes

**The action scripts never call `reaper.defer`.** This matters. If a script is
still alive when you press its key again, REAPER interrupts you with a "script
is already running — terminate or launch new instance?" prompt, which makes
fast key repeat impossible and, if you answer "terminate" and tick remember,
permanently costs you every second keypress.

So preview note timing lives in `MidiGrid_Daemon.lua`, a single background loop
that auto-starts on first use and relaunches itself if it ever dies. Action
scripts post a request to transient `ExtState` and exit within a millisecond. A
new request cuts the previous note, so fast arrowing retriggers cleanly. The
daemon releases everything on `atexit`, so notes cannot hang.

Preview requests use **non-persisted** `ExtState` — persisting them would write
to `reaper.ini` on every keypress.

## Tunables

In `ExtState` section `midigrid`:

| Key | Default | Meaning |
|---|---|---|
| `vel` | 96 | Velocity of inserted notes |
| `velstep` | 8 | Velocity change per keypress |
| `chan` | 0 | MIDI channel (0-based) |
| `previewdur` | 0.4 | Preview note length, seconds |

## Tests

`test_lib.lua` covers the pure logic — scale stepping, note naming, grid
labels — against a stubbed `reaper` table, so it runs outside REAPER:

```
lua test_lib.lua
```

Everything touching MIDI data or the REAPER API is only exercised in REAPER
itself.

## Limitations

- Preview uses `StuffMIDIMessage`, which plays through the track's instrument
  via the virtual-keyboard input, so the track must be armed / monitored —
  exactly as with REAPER's own MIDI preview.
- The grid aligns to the project timeline (bar lines), not the item start. For
  an item starting off-grid, the first cell will be partial.
- Note octave naming follows the `midioctoffs` preference; with the default,
  note 60 reads as C5.