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lightcraft/docs/control-protocol.md
T
Brandon ThomasandClaude Opus 5.5 103f53724f LR-FILMSTRIP: grid and filmstrip keep the user's scroll position; wheel scrolls the filmstrip
Fixes #11.

Root cause: the grid and the filmstrip remembered the last active photo in egui temp data
with mismatched types (inserted `Option<PhotoId>`, read back as `PhotoId` because of the
`let last: Option<PhotoId> = get_temp(..)` annotation), so the read always missed, "the
active photo changed" was true on every frame and both called `scroll_to_rect` on the
active photo every frame. Any wheel or scroll-bar scroll was undone as soon as the user
stopped (the animated scroll back read as a delayed snap).

- `grid::follow_active` (shared by grid and filmstrip): scroll to the active photo only
  when it changed since the strip was last drawn, or when the strip was not drawn on the
  previous pass (view switch). Time passing, finished renders, edits and a released scroll
  bar no longer move either strip.
- Filmstrip: a vertical mouse wheel scrolls it sideways (horizontal trackpad scrolling
  still works); it recentres on a new active photo only when that is off screen, so a
  click on a visible thumbnail leaves it alone.
- `ui.inspect` reports `scroll: {grid, filmstrip}`; headless tests in `tests_scroll.rs`.
- docs/parity.md (LR-VIEW-PHOTOGRID, LR-VIEW-FILMSTRIP), docs/control-protocol.md.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
2026-10-04 02:56:32 -04:00

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# Control protocol
`lightcraft --control 7980` (or `LIGHTCRAFT_CONTROL_PORT=7980`) starts a JSON-lines server on
`127.0.0.1:7980` (loopback only). One request per line, one reply per line, in order:
```text
→ {"id": 1, "method": "engine.execute", "params": {"command": "photo.rate", "params": {"rating": 4}}}
← {"id": 1, "ok": true, "result": null}
← {"id": 2, "ok": false, "error": "unknown command `nope`"}
```
Requests are answered on the UI thread between frames (timeout 60 s). The MCP server's connect
mode ([mcp.md](mcp.md)) is a thin layer over this channel. Implementation:
`crates/ui-egui/src/control.rs` (methods) and `apps/lightcraft/src/control_server.rs` (transport).
## Methods
| Method | Params | Result |
|---|---|---|
| `engine.execute` (alias `ui.menu.invoke`) | `{command, params?}` | Run any engine or UI command (see `engine.commands`) |
| `engine.commands` | — | Engine + UI commands: id, label, menu, shortcut, params doc, enabled |
| `ui.menu.list` | — | Menu entries (flat: id, label, menu path, shortcut, enabled) |
| `ui.menu.tree` | — | The menu bar as shown (File … Help): items `{id, params?, label, shortcut?, enabled, checked?}`, separators, submenus — the model behind the native macOS menu bar and the in-window menus |
| `ui.inspect` | — | UI state, window, canvas/image rects, `scroll: {grid, filmstrip}` (scroll offsets in points, `null` until drawn), active photo, selection, perf, status, memory (bytes per cache, see `library.memory`; plus stage caches and textures), `export: {running: {total, done, current} \| null, last}` |
| `ui.widgets` | `{filter?}` | On-screen widgets `{id, rect: [x, y, w, h]}` (screen points) |
| `ui.clickWidget` / `ui.dragWidget` / `ui.hoverWidget` | `{id, count?, fx?, fy?}` / `{id, toX?, toY?, dx?, dy?, steps?}` / `{id, fx?, fy?}` | Real egui input on a widget (hover: the pointer rests on it, e.g. for preset/profile previews) |
| `ui.move` / `ui.click` / `ui.drag` | `{x, y, count?, button?}` / `{x, y, toX, toY, steps?}` | Raw pointer input, screen points |
| `ui.pointer` | `{events: [{kind: down\|drag\|up, x, y}], alt?, shift?, cmd?}` | Gesture in normalized image coordinates (Detail view) |
| `ui.key` | `{key, cmd?, shift?, alt?, ctrl?}` | Key press |
| `ui.text` | `{text}` | Text input |
| `ui.scroll` | `{dx, dy}` | Mouse wheel |
| `ui.set` | partial UI state, e.g. `{"view": "detail"}` | Resulting UI state |
| `ui.dialog.confirm` / `ui.dialog.cancel` | — | Close the open dialog |
| `ui.resize` | `{width, height}` | Resize the window |
| `ui.screenshot` | `{path?, headless?}` | `{path, width, height}` once the frame (with finished renders) is captured. `headless: true` draws the UI on the CPU (no compositor needed); a windowed capture that gets no frame within 2 s falls back to headless automatically |
| `engine.execute {command: "app.export", params}` | export params (see `docs/mcp.md`), plus `preset`, `dir` / `path`, `ids`, `background` | Writes the files and returns `{files}`; with `background: true` (what the Export dialog and menus use) it returns `{background: true, total}` at once and the batch runs on a worker thread — poll `ui.inspect` → `export` |
| `ui.render` | `{id?, size?, path?}` | Render a photo (PNG to `path`), `{width, height}` |
| `app.quit` | — | Close the app |
## Headless rendering (no window, no GPU)
The egui UI can be rasterized on the CPU (`crates/ui-egui/src/softpaint.rs`, driven by
`crates/ui-egui/src/headless.rs`): same tessellation, gamma-space premultiplied blending and
scissor clipping as egui's GPU backends, so the image matches the window (minus GPU dithering).
- **In the running app:** `{"method": "ui.screenshot", "params": {"path": "a.png", "headless": true}}`.
The UI is drawn into an offscreen context from the app's logic tick, which keeps running when the
window is occluded or the display sleeps/locks. Windowed screenshots fall back to this after 2 s.
- **Without any app window:** `lightcraft-cli snapshot` runs a whole app session headlessly and
answers the same control requests (same handler) from a JSON-lines script:
```text
lightcraft-cli snapshot --demo -o grid.png --size 1600x1000 [--scale 2]
lightcraft-cli snapshot --library DIR --script tour.jsonl -o shot.png
```
`tour.jsonl` holds one request per line (`#` comments allowed), e.g.
`{"method": "ui.set", "params": {"view": "detail", "right": "edit", "openSections": ["optics"]}}`
then `{"method": "ui.screenshot"}`. Replies are printed to stdout. A `ui.screenshot` without
`path` writes `-o` (then `OUT-2.png`, `OUT-3.png`, …); `ui.settle {timeoutMs?}` waits until no
renders are in flight. Each request runs frames until it is answered and its injected input
(clicks, keys, drags) has played out. Widget ids for `ui.clickWidget` come from `ui.widgets`
(e.g. `button:upright-auto`). A 1600×1000 demo snapshot takes ~1–2 s (debug build).