# ScanSlicer (fork) — Project Guide

Purpose of this file: give any LLM working in this repo enough context to be
effective without re-reading everything. Keep it current as the code changes.

## What this project is

ScanSlicer is a desktop Qt application (Python/PySide6) that detects multiple
photos in a flatbed scan image, lets the user correct each box manually, then
exports perspective-corrected crops. Inspired by
[PhotoSlicer](https://github.com/francescovannini/photoslicer) (Francesco
Vannini). Runs on Linux over Wayland or X11.

This repo is a **local fork** of
[macrodev8/ScanSlicer](https://github.com/macrodev8/ScanSlicer) (upstream owner
inactive). License: GNU GPL v3 (must be preserved). Attribution: keep upstream
credit and the "inspired by PhotoSlicer" note.

## Goals of this fork

1. Fix the mirrored-export orientation bug and add an explicit left/right
   orientation workflow (implemented, see below). This is the primary patch.
2. Keep the app usable on the maintainer's own photo scans; afterwards only
   minimal maintenance is expected.
3. Push to the maintainer's Forgejo instance at `code.dgerdesmann.de` (no
   GitHub fork). Keep licensing, attribution, and repository description proper.

The maintainer is primarily an R user and new to Python/Git. Changes should be
small, self-checked, clean, and secure; do not assume the maintainer can vet
Python code.

## The orientation fix (implemented)

The bug: exported slices could come out mirrored (left/right swapped). Root
cause is `PhotoSlice.normalize_top_left()` (in `slices.py`), which re-derives
"top" from geometry — it picks a top-left corner and resolves winding so edge
0→1 is the "most horizontal" top edge. That inference is ambiguous, and because
`squarize()` and `reset_rotation()` both re-run `normalize_top_left()` at the
end, any manual correction was silently overwritten.

The fix adds an explicit left/right orientation workflow:

- `PhotoSlice.swapped` — persistent flag (default `False`): "user has explicitly
  mirrored left/right".
- `PhotoSlice.swap_left_right()` — toggles `swapped` and reindexes the corners
  `[TL,TR,BR,BL] -> [TR,TL,BL,BR]` (i.e. `bbox[[1,0,3,2]]`), a pure left/right
  mirror that keeps the top (edge 0→1) and bottom edges in place. NOTE: the
  earlier `[0,3,2,1]` reindex was wrong — it rotated the quad 90°.
- `normalize_top_left()` applies the same `[1,0,3,2]` reindex when `swapped` is
  true (after its geometric inference), so manual orientation survives
  `squarize()` / `reset_rotation()`.
- "Swap L/R" toolbar button (`ui_builders_preview.py`) ->
  `CanvasStateMixin.swap_active_slice_left_right()` ->
  `ScanSlicerCanvasActionsMixin.swap_active_box_left_right()`.
- Visual indication in `CanvasRenderMixin.paintEvent()` (`canvas_render.py`):
  corners color-coded left = orange, right = cyan; edges colored red = top
  (0→1), green = right (1→2), orange = bottom (2→3), and the left edge (3→0)
  follows lock state (blue locked / lightgreen unlocked).

## Key implementation facts

- `PhotoSlice.bbox` is a 4×2 numpy array in the order
  `[top-left, top-right, bottom-right, bottom-left]`.
- `Autoslicer.save_slice()` (in `autoslicer.py`) builds the perspective
  transform assuming the `[TL,TR,BR,BL]` order. Do NOT change that contract
  without updating every consumer.
- `PhotoSlice.squarize()` and `reset_rotation()` call `normalize_top_left()` at
  the end; the `swapped` flag makes that safe for manual orientation.

## Repository structure

```
scanslicer/                 application source (package)
  entry.py                  CLI parsing, Wayland/X11 backend selection
  main.py                   QtScanSlicer main window, theme, app bootstrap
  controller*.py            UI action handlers (status, canvas, detection,
                            image I/O, params)
  ui_builders*.py           widget construction (controls, preview, shared)
  canvas*.py                interactive canvas (interaction/render/state mixins)
  slices.py                 PhotoSlice geometry model + polys_iou
  autoslicer.py             detection/export engine wrapper (save_slice)
  autoslicer_detection.py   detection pipelines, contour→box extraction
  autoslicer_feedback.py    auto-tune profiles, scoring, feedback persistence
  params.py                 parameter model, defaults, presets
packaging/appimage/         AppImage recipe + build scripts (preferred deploy)
Dockerfile                  container runtime image
docker-compose.yml          GUI container wiring
pyproject.toml              package metadata + dependencies (uv.lock pinned)
docs/                       user-guide, architecture, parameters, autotune,
                            runtime-config, appimage, development
```

## Architecture in brief

- `QtScanSlicer` (`main.py`) is a `QMainWindow` composed from UI builder mixins
  and controller mixins.
- `QtSlicingCanvas` (`canvas.py`) = interaction + render + state mixins; holds
  the image, zoom/pan state, and the list of `PhotoSlice` objects.
- Background work (detection, auto-tune) runs on a single-worker `QThreadPool`;
  results are delivered back to the UI via Qt signals.
- Export flow: `save_all()` (`controller_image_io.py`) loops over locked slices
  and calls `Autoslicer.save_slice(bbox, path, params)` for each.

## Run / build

```bash
uv sync --frozen
uv run scanslicer /path/to/scans     # or: python -m scanslicer
```

- AppImage (preferred): `bash packaging/appimage/build-appimage.sh`
- AppImage via Docker: `bash packaging/appimage/build-appimage-docker.sh`
- Docker runtime: `docker compose up --build`
- Dependencies (from `pyproject.toml`): PySide6, opencv-python-headless, numpy.
- Python >= 3.10; dev env is Python 3.12 in `.venv`.

### AppImage build: Docker context gotcha

The maintainer's Docker points at Docker Desktop (`desktop-linux` context). Its
bind-mount filesystem forbids `chown`, but `appimage-builder` needs root
ownership while extracting `.deb` packages, so the build fails with
`dpkg-deb ... Cannot change ownership to uid 0, gid 0: Operation not permitted`.

Workaround: run the Dockerized build against the native daemon (or switch
context with `docker context use default`):

```bash
DOCKER_HOST=unix:///var/run/docker.sock bash packaging/appimage/build-appimage-docker.sh
```

Output lands in `appimage/dist/ScanSlicer-<version>-x86_64.AppImage` (the
`appimage/` dir is git-ignored).

## Config / persistence

Runtime files live in `~/.config/scanslicer/` (or `$XDG_CONFIG_HOME/scanslicer/`)
by default: `defaults.json`, `presets.json`, `autotune-feedback.json`,
`status.log`. Paths are overridable via `SCANSLICER_*_PATH` env vars. In the
Docker setup these land in `./.scanslicer/` on the host.

## Notes

- No automated test suite exists; validate changes by running the app on sample scans (startup, detection, save, auto-tune).