# Development guide

## Prerequisites

- Rust stable (1.90+). Add the web target with `rustup target add wasm32-unknown-unknown`.
- macOS, Windows or Linux. Linux needs `libxkbcommon-dev libwayland-dev libx11-dev libxrandr-dev libxi-dev libgl1-mesa-dev libgtk-3-dev`.

## Build and run

```sh
cargo run --release -p photocraft -- path/to/image.psd      # desktop app
cargo run --release -p photocraft -- --control 7878 --control-token-file .private/control.token img.jpg
cargo test --workspace                                     # everything
cargo xtask ci                                             # fmt + clippy + tests + layers + wasm
cargo xtask stats                                          # tests and lines per crate
cargo xtask parity                                         # Photoshop menu coverage -> docs/parity.md
```

Image code is slow at `opt-level 0`, so the workspace profile builds dependencies at `opt-level 2`. Use `--release` for anything interactive.

## Environment variables

| Variable | Effect |
|---|---|
| `PHOTOCRAFT_CONTROL_PORT` | Same as `--control <port>` |
| `PHOTOCRAFT_CONTROL_TOKEN` | 64-hex bearer token for control TCP (avoid on shared systems where environment inspection is possible) |
| `PHOTOCRAFT_CONTROL_TOKEN_FILE` | Read, or create for a server, the control bearer-token file |
| `PHOTOCRAFT_CPU_CANVAS=1` | Force the CPU canvas path instead of the wgpu shader canvas |
| `PHOTOCRAFT_GPU_TILE=2048` | Force GPU canvas tiling (tests tile seams) |
| `PHOTOCRAFT_FX_NOCACHE=1` | Bypass the CPU layer-effect map cache (`compose::effect_maps`) |
| `PHOTOCRAFT_CPU_COMPOSE=1` | Keep the wgpu canvas but composite on the CPU (compare GPU vs CPU renders, e.g. with the snapshot example) |
| `PHOTOCRAFT_FX_TRACE=1` | Print the CPU time spent on GPU effect shapes and distance fields per rebuild |
| `PHOTOCRAFT_THEME_FILE=tokens.json` | **Debug builds only:** live design-token overrides, re-read on change |

### Live design tokens

```json
{ "card": "#323232", "tab_strip": "#262626", "accent": "#378ef0", "radius": 4 }
```

Keys are the field names of `theme::Tokens` (`crates/ui-egui/src/theme.rs`). Edit and save the file while the app runs to see changes immediately, with no recompile. This is compiled out of release builds.

## Driving the app programmatically

Start the app with a private token file. It then accepts authenticated JSON lines on `127.0.0.1:7878`:

```sh
TOKEN=$(tr -d '\r\n' < .private/control.token)
printf '%s\n' "{\"id\":\"auth\",\"method\":\"auth\",\"params\":{\"token\":\"$TOKEN\"}}" \
              '{"id":1,"method":"engine.execute","params":{"command":"layer.newAdjustmentLayer.hueSaturation","params":{"hue":30}}}' \
              '{"id":2,"method":"ui.screenshot","params":{"path":"/tmp/shot.png"}}' | nc 127.0.0.1 7878
```

See `docs/control-protocol.md` for every method. Tips:

- **macOS does not render occluded windows.** `ui.screenshot` raises the window first (`focus: true` by default). Use `ui.focus` before other visual checks.
- **Capture only our own window.** For native captures (to see the real title bar and traffic lights), capture by window id (`screencapture -l <CGWindowID>`), never a screen region, which can grab other apps.
- **Pointer gestures:** `ui.pointer` takes events in *document* coordinates and runs them through the same tool state machine as the mouse.

## Headless CLI

`apps/photocraft-cli` builds the binary `photocraft-cli`:

```sh
cargo run -p photocraft-cli -- convert in.psd out.pcraft               # any supported format -> any
cargo run -p photocraft-cli -- info out.pcraft                          # JSON: size, mode, depth, layer tree
cargo run -p photocraft-cli -- run in.png --cmd layer.new.layer --params '{"name":"Ink"}' \
                                          --cmd filter.blur.gaussian --params '{"radius":3}' --out out.psd
cargo run -p photocraft-cli -- run --new '{"width":800,"height":600}' --cmd document.inspect
cargo run -p photocraft-cli -- batch --actions actions.json --in photos/ --out done/ --format jpg
cargo run -p photocraft-cli -- commands --filter blur                    # the command registry
```

`actions.json` is `[{"command": "<id>", "params": {…}}, …]`, which is the same shape as a recorded action. `run` prints one JSON line per command result.

## Native format (.pcraft)

`crates/format` defines the lossless native bundle. It is either a ZIP of STORE entries or a directory with the same layout:

- `manifest.json`: the versioned document tree, with migrations in `format/src/migrate.rs`.
- `tiles/<blake3>.zst` and `blobs/<blake3>.zst`: zstd-compressed objects, content-addressed by the BLAKE3 hash of their uncompressed bytes.
- `thumb.png` and `composite/preview.png`: previews.

Keep one `PcraftWriter` per open document: re-saving then only compresses and writes tiles that changed, and directory bundles garbage-collect unreferenced objects. `format::Autosaver` writes snapshots into a recovery directory on a background thread. `list_recovery` / `recover` / `discard_recovery` implement crash recovery.

`photocraft-io` routes `.pcraft` through this crate in `import`/`export`, detecting it by magic or by extension.

## MCP (agents)

`photocraft-cli mcp` serves MCP on stdio using `crates/automation`, which is built on `rmcp`:

- **Headless:** `photocraft-cli mcp`. It drives an in-process engine session.
- **Live app:** start `photocraft --control 7878 --control-token-file <private-path>`, then run `photocraft-cli mcp --bridge 127.0.0.1:7878 --control-token-file <private-path>`. See `docs/control-protocol.md#mcp-bridge`.

Tools:

- `session_list`
- `doc_open`, `doc_new`, `doc_save`, `doc_export`, `doc_inspect`, `doc_render_preview` (returns a PNG image), `doc_select`, `doc_close`
- `command_list`, `command_run`, `command_batch` (several commands per call)
- bridge only: `ui_inspect`, `ui_screenshot`, `ui_pointer`, `ui_menu_invoke`, `ui_set`, `control_call`

Claude Code (`.mcp.json` in the repo root, or `claude mcp add`):

```json
{
  "mcpServers": {
    "photocraft": {
      "command": "/path/to/photocraft/target/release/photocraft-cli",
      "args": ["mcp"]
    },
    "photocraft-live": {
      "command": "/path/to/photocraft/target/release/photocraft-cli",
      "args": ["mcp", "--bridge", "127.0.0.1:7878", "--control-token-file", "/private/path/photocraft-control.token"]
    }
  }
}
```

```sh
cargo build --release -p photocraft-cli
claude mcp add photocraft -- "$PWD/target/release/photocraft-cli" mcp
```

`doc_inspect` (and the engine command `document.inspect`) reports the layer tree with kinds,
bounds, masks, selection, effects (`effects.items[].kind`), smart filters (`smartFilters[]`), type
text, adjustment settings, channels and history, so agents can verify what they did without a
screenshot. `crates/automation/tests/agent_tasks.rs` is the reference: ten realistic edit tasks
(title card, colour grade, undo/redo, editable smart blur, masks, saved selections, align, layer
export, resize/crop, CMYK + native save) driven purely over MCP.

Without MCP, `photocraft-cli serve [--port N]` keeps a headless session open and answers JSON lines
(see `docs/control-protocol.md#headless-server`).

A typical agent loop:

1. `doc_open {path}`
2. `command_list {filter:"blur"}`
3. `command_run {id:"filter.blur.gaussian", params:{radius:4}}`
4. `doc_render_preview` to check the result
5. `doc_save {path:"out.pcraft"}`

## Colour management

`crates/cms` is our own pure-Rust ICC engine (v2/v4 parsing, matrix/TRC and LUT profiles, all four
intents, black point compensation). It ships CC0 built-in profiles, including a synthetic
"Photocraft Coated CMYK", because Adobe's CMYK profiles are proprietary (see `crates/cms/README.md`).

- Documents carry an optional embedded ICC profile (`Document::icc_profile`); `edit.assignProfile`
  and `edit.convertToProfile` change it. Mode changes (`image.mode.*`) convert through cms.
- **Proof Colors** (⌘Y), **Proof Setup** and **Gamut Warning** (⇧⌘Y) bake a 3D LUT
  (`cms::Lut3d`) that the canvas shader applies; the document pixels never change.
- Convert colours with `photocraft_cms::transform::cached(src, dst, opts)`: transforms are cached
  process-wide and integer buffers use precomputed tables or a device link.

## Menu parity

`cargo xtask parity` compares Photoshop's menu tree (`crates/ui-egui/src/menu_catalog.rs`) with
the live command registry (`menus::is_live`) and rewrites [`docs/parity.md`](parity.md). The test
`parity::tests::parity_does_not_regress` fails if the live count drops below `parity::FLOOR`.

## Testing strategy

- **Unit and property tests** in every crate. proptest is used for tile COW, regions and codecs.
- **Format crates:**
  - synthetic generators (`psd::testgen`)
  - byte-exact round trips
  - malformed-input sweeps (truncate at every offset)
  - fuzz targets (`crates/*/fuzz`)
- **Real-file corpus** in `corpus/` (gitignored). `corpus/psd` holds MIT-licensed test PSDs, listed with their sources in `corpus/psd/SOURCES.md`, and `cargo xtask corpus --download` fetches PngSuite. Tests skip silently when a corpus is absent.
- **Composite oracle:** a PSD's embedded merged image is compared with our compositor's output. The pass rate is tracked in the roadmap.
- **UI:** unit tests for widgets and state, plus screenshot checks through the control channel.

## Performance notes

- The canvas is presented by a custom WGSL shader (`ui-egui/src/gpu_canvas.rs`): mip-mapped/nearest sampling, procedural checkerboard, pixel grid, tiling. Brush strokes upload only their damage rect.
- **The canvas composites on the GPU** (`photocraft-gpu`, driven from `gpu_canvas.rs`), layer effects included. What the planner can't express returns `Unsupported` and the canvas falls back to the CPU compositor (`photocraft-compose`, also the reference for export and tests): Multichannel documents, and documents or effect regions over the texture limit. Pieces the GPU can't derive itself are rasterised once on the CPU and cached (`compose::masks` for vector masks, `compose::shape_split` for stroked shapes with clipped layers, effect distance fields). Timings of the interactive paths: `cargo run --release -p photocraft-ui-egui --example interactive_bench`; effects: `--example fx_bench` (`--compare files…` for GPU vs CPU). Rendering fidelity: `cargo run --release -p photocraft-io --example oracle_diff -- corpus/psd` (the whole PSD oracle table in seconds). `ui.inspect` → `perf.timings.gpuFallback` names the reason (`null` on the GPU path).
- **Layer effects on the GPU** (`gpu/src/fx.rs`, kernels in `gpu/src/compose.wgsl`). Every enabled effect becomes a *map program* over the layer's effect region (shift, dilate, Gaussian blur, glow ramp, bevel height and shading, contour, stroke band), mirroring `compose::effects` step by step; the chunked composite then paints through the maps, clipped to that region, and copies the result back into the backdrop in place, so a small text layer costs only its own pixels. The layer's shape (`compose::layer_shape`) and its distance fields (`compose::effects::distance_field`: a sequential transform whose tie-breaking a parallel GPU pass can't reproduce bit for bit) come from compose on the CPU, computed in parallel bands. Everything is cached per layer state: an unrelated edit, or an effect's colour or opacity, rebuilds nothing; a brush dab recomputes the touched 256² tiles grown by the effect reach; changing one effect's geometry rebuilds that effect only. Cache budget `gpu::FX_BUDGET` (1.5 GB, least recently drawn layers evicted first). `PHOTOCRAFT_FX_TRACE=1` prints the CPU time of each rebuild.
- The canvas grows a stroke's damage rect by the effect reach of the layers around it (`canvas::effect_reach`), so effects beyond the dab refresh too (on both paths).
- **Numbers** (7360 × 4912, 8 text layers + one painted layer with drop shadow + stroke + bevel, Hue/Saturation on top; M4 Pro; `cargo run --release -p photocraft-ui-egui --example fx_bench`), CPU fallback → GPU: full refresh with warm effect maps 5.7 s → 47 ms; Hue/Saturation tweak above the effects 4.7 s → 31 ms; brush dab on a plain layer 32 → 1.7 ms; brush dab on the effect layer (its maps rebuilt around the dab) 659 → 3.7 ms; first refresh (all maps built) 6.4 s → 0.39 s. With the CPU ~14× oversubscribed by parallel builds (min of 7 runs): 8.1 s → 0.33 s, 9.9 s → 0.28 s, 28 → 2.2 ms, 1.7 s → 89 ms; moving a text layer 7 px 336 → 13 ms. `fx_bench --compare corpus/psd/…/*.psd` reports the GPU vs CPU difference on real files (30 of the 31 corpus files with effects render on the GPU, worst 0.12/255).
- On the CPU path `compose::effect_maps` caches shadow, glow, bevel and satin maps per layer state (LRU, 768 MB budget).
- Live adjustment previews on large documents use a downsampled proxy (`ui-egui/src/proxy.rs`).
- `ui.inspect` returns `perf` timings (UI ms per frame, composite ms, upload ms).
- Never scan full surfaces per frame. Cache per document revision (`PhotocraftApp::cached_bounds`). An uncached `content_bounds()` on a 36 MP layer once cost 77 ms per frame.

## Web build

`apps/photocraft-web` runs the same `PhotocraftApp` in the browser through eframe's web runner. The renderer is wgpu: WebGPU where the browser has it, WebGL2 otherwise. It is Rust only. The only JavaScript is the glue that wasm-bindgen generates.

```sh
brew install trunk                 # or: cargo install trunk --locked
cd apps/photocraft-web
trunk build --release              # writes ../../dist/web (index.html, .js glue, .wasm)
trunk serve --release              # dev server on http://127.0.0.1:8765
```

Any static file server works for `dist/web`, for example `python3 -m http.server 8765` run inside that directory. Trunk downloads the matching `wasm-bindgen` and `wasm-opt` itself. The release `.wasm` is about 12.7 MB, or 5.0 MB gzipped. Serve it with compression.

URL flags: `?webgl` forces the WebGL2 backend, and `?cpu` forces the CPU canvas path.

How the web shell (`apps/photocraft-web/src/web.rs`) differs from desktop:

- **Open** uses `rfd::AsyncFileDialog`. The bytes arrive asynchronously in `Services::inbox`, which the app drains every frame.
- **Save / Save As / Export** trigger a browser download of the encoded bytes. The shell does this with a Blob, an object URL and a temporary `<a download>`, all created from Rust. There is no save dialog, so the suggested name becomes the download name.
- **Drag-and-drop:** `WebShell` takes the frame's `dropped_files` before the app sees them. It reads each file with `DroppedFile::bytes_async` and pushes the bytes into the inbox.
- **No control server:** browsers can't listen on TCP. To automate the web build, drive headless Chrome with `--remote-debugging-port`. `Page.setInterceptFileChooserDialog` plus `DOM.setFileInputFiles` covers Open, `Input.dispatchDragEvent` with `files` covers drops, and `Browser.setDownloadBehavior` captures downloads.
- Headless Chrome on macOS (`--headless=new --enable-unsafe-webgpu`) gets a real WebGPU adapter.


## Offscreen UI snapshots (no window)

Render the full UI headlessly with the real wgpu canvas, e.g. for design reviews or when the app
window would be occluded (macOS doesn't render occluded windows, so live `ui.screenshot` must raise
the window and steal focus):

```sh
cargo run --release -p photocraft-ui-egui --example snapshot -- \
    --out ui.png --size 1440x900 --scale 2 --open photo.jpg \
    --script '[["ui.set", {"tool": "type"}], ["ui.menu.invoke", {"id": "image.canvasSize"}]]'
```

`--script` is a list of control-protocol calls (`[method, params]`), applied in order.
Input calls (`ui.key`, `ui.type`, `ui.click`) now reply only after the app has processed the events,
so a following `ui.inspect` observes their effect.


## Rendering fidelity (PSD oracle)

`cargo test --release -p photocraft-io --test corpus -- --nocapture` compares our composite of every
corpus PSD with Photoshop's own merged image (PASS ≤ 2/255). To dig into one file:

```sh
cargo run --release -p photocraft-io --example oracle_diff -- corpus/psd/<file>.psd 0 png /tmp/diff.png
```

writes ours | Photoshop | a diff heatmap side by side; `col`, `row`, `worst [n]`, `grid x0 y0 x1 y1 [ch]`,
`layerpx x y` and `DUMP_FX=1` print samples, the worst pixels, value grids, per-layer pixels and raw
effect descriptors. Findings so far: fill-layer gradients are framed by the layer's mask bounds;
Photoshop's gradient Smoothness is a Catmull-Rom blend and "Perceptual" interpolation is Oklab
(baked into dense stops on import, `crates/io/src/gradient_bake.rs`); a shape layer's vector
stroke is drawn above its clipped layers; linked effect patterns tile from the layer's `fxrp`
reference point; stroke distances follow a 5 × 5 chamfer metric (1, √2, √5) seeded at sub-pixel
edge offsets; interior effects keep the layer's alpha; outside strokes blend onto the backdrop with
their own modes, an upper stroke covering lower ones.