photocraft/docs/development.md

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

cargo run --release -p photocraft -- path/to/image.psd      # desktop app
cargo run --release -p photocraft -- --control 7878 img.jpg # with the JSON control server
cargo test --workspace                                     # everything
cargo xtask ci                                             # fmt + clippy + tests + layers + wasm
cargo xtask stats                                          # tests and lines per crate

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_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_THEME_FILE=tokens.json	Debug builds only: live design-token overrides, re-read on change

Live design tokens

{ "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 --control 7878. It then accepts JSON lines on 127.0.0.1:7878:

printf '%s\n' '{"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:

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, then run photocraft-cli mcp --bridge 127.0.0.1:7878. 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
• 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):

{
  "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"]
    }
  }
}

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

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"}

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.
• Compositing is still CPU (photocraft-compose). Live adjustment previews on large documents use a downsampled proxy (ui-egui/src/proxy.rs). The GPU compositor is milestone M5.
• 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.

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):

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:

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 and DUMP_FX=1 print samples 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.