effector/CLAUDE.md

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Build and test

cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build
ctest --test-dir build --output-on-failure

Everything is warning-clean under -Wall -Wextra -Wpedantic; keep it that way.

The test suite is a single hand-rolled binary (no framework), so there is no per-test filter: run ./build/tests/effector_tests directly to see the section headings (rng, registry, scanlines, tiles, blur, chain, project, image io, batch loading) and the ok/FAIL lines. To iterate on one area, comment out the other blocks in tests/core_tests.cpp or add a new std::cout << "section\n" block — checks are plain check(condition, "description") calls and main() returns the failure count.

Headless render (no display needed, the fastest end-to-end smoke test):

build/effector -o /tmp/out.png -s 800x600 --strip-height 6 --seed 1 a.jpg b.png

Running the GUI from this shell

GTK picks Wayland from an inherited WAYLAND_DISPLAY and will not draw into an Xvfb display, which silently yields black screenshots. Under Xvfb always use:

env -u WAYLAND_DISPLAY GDK_BACKEND=x11 DISPLAY=:79 build/effector ...

Architecture

The plug-in contract is declarative

Effect (src/core/effect.hpp) exposes params() returning std::vector<ParamSpec> (src/core/params.hpp). Those specs are the only thing the GUI and CLI know about an effect: src/gui/window.cpp builds SpinButtons/Switches/DropDowns/file choosers from them and src/cli/options.cpp generates flags from them (strip_height → --strip-height). Never add effect-specific branches to the GUI or the parser — add a ParamSpec instead. A Path param names a file on disk; like a source path it is written relative to the project folder. A Text param is free-form text the user types, and a Color param is a colour written #rrggbb (parseColor/formatColor/paramColor in src/core/params.hpp), shown as a colour button in the interface. Values travel as ParamValues (a map<string, variant<long,double,bool,string>>), read back with paramInt/paramDouble/paramBool/paramChoice.

Whether an effect works from the loaded photographs is part of the same contract: Effect::needsSources() (default true, false for blur). Only the first stage ever sees the sources, so chainNeedsSources (src/core/chain.cpp) just asks the first stage — a chain led by blur renders with no images loaded at all, and both front-ends gate on that rather than on "are there any images".

Adding an effect: new src/effects/<name>.{hpp,cpp} subclassing Effect, one line in the registry list in src/core/registry.cpp, one line in the effector_core sources in CMakeLists.txt. Nothing else — it shows up in the CLI, in the chain menu and as a cascade stage on its own.

Effects cascade

Effects are never applied on their own: renderChain (src/core/chain.cpp) runs a std::vector<ChainStage> in order, handing stage 0 the loaded sources and every later stage the previous stage's output as its only source. That is the whole of the cascade — an effect neither knows nor cares whether its input came from disk. All stages share one Rng and run strictly in sequence, so a seed still reproduces the cascade byte for byte.

A stage carries a ChainStage::enabled flag, and enabledStages (src/core/chain.cpp) is the one place that reads it: a disabled stage is skipped whole — handed no image and drawing nothing from the shared rng — so switching one off renders exactly what the chain rendered before it was added. renderChain, chainNeedsSources, chainTitle and chainSlug all go through it, which is why the status line and the file name never mention a stage that did not run. A chain with every stage disabled throws rather than rendering nothing.

The interface builds the chain in the sidebar ("Effect chain": add from the menu, reorder, remove, switch off with the check on the row, one stage selected at a time with its params below), the CLI builds it from repeated -e: -e scanlines --strip-height 6 -e blur --radius 5, with --disable NAME leaving a stage in place but skipping it. Flags share one namespace across all effects, so buildChain (src/cli/options.cpp) hands each flag to the stage whose effect declares it — two effects must not declare the same param key.

The canvas is a format or plain pixels

src/core/canvas.cpp holds the one table of standard sizes both front-ends offer: web formats are a fixed pixel size, print formats a sheet in millimetres that becomes pixels at a dpi. Adding a format is a line in canvasFormats() — the dropdown, --format and --help all walk that table. The pixels stay the truth everywhere (renderChain never hears about formats); a format is the presentation of a canvas, carried alongside the pixels in Options and Project and empty for a custom size. Where a format is named it decides the pixels, so a project saved as A4 reopens as A4.

Projects are plain JSON

src/core/project.cpp reads and writes the whole setup — source paths, the chain with its params (and its "enabled": false, written only for a stage that is switched off), canvas and seed — as a small JSON file, with its own minimal reader rather than a JSON dependency. Writing is driven by the effects' ParamSpecs, not by whatever happens to sit in a stage's ParamValues, so a key an effect does not declare is never written and never read back: an old project keeps the defaults for params that did not exist when it was saved. Source paths under the project's own folder are written relative, so a folder can be moved or shared whole.

The interface opens and saves projects from the header-bar menu (New, Open, Save, Save As, with the usual Ctrl+N/O/S accelerators); the window title shows the project name. Opening one replaces the sources, so a decode still in flight is discarded rather than mixed into the new project (dropLoadedImages_).

Two link targets, deliberately

effector_core (static) holds image IO, params, effects, rng and links only gdk-pixbuf-2.0, pangocairo (the text effect's glyphs; Pango and Cairo need no display) + Threads — no gtkmm, no display. The effector executable adds src/main.cpp, src/cli/, src/gui/ and links gtkmm. Keep GTK out of src/core/ and src/effects/; the tests link the core alone and rely on this.

Determinism is a contract

Rng (src/core/rng.hpp) is a hand-written xoshiro256** rather than <random>, because libstdc++ distributions are not portable across implementations. Same sources + settings + seed must produce byte-identical output on any machine — the tests assert this. The one thing outside this is the text effect's glyphs, which are whatever shapes the machine's fonts and fontconfig give: everything it is handed, the rng included, is still used the same way. Effects must draw every random value from the Rng& they are handed, and must not depend on thread scheduling: the scanlines effect first draws the whole strip plan serially from the rng, then copies pixels in parallel.

Threading model

• parallelFor (src/core/parallel.hpp) splits fixed contiguous chunks across hardware threads — used for pixel work, where items cost the same.
• loadImages (src/core/image.cpp) deliberately does not use parallelFor: files vary wildly in size, so workers pull the next index from a shared std::atomic cursor. It reports through LoadProgress::onFile (called from decoding threads: must be thread-safe and non-blocking) and aborts when LoadProgress::cancel is set, in which case the partial result is discarded by the caller, not used.
• The GUI never blocks the main thread. Both decoding and rendering run on a std::thread and signal back with a Glib::Dispatcher (loadProgress_/loadFinished_/renderDone_ in src/gui/window.hpp); the handlers are the only code that touches widgets. Renders are coalesced through a debounce timer (requestRender() → startRender()), and the progress window is created on a 250 ms delay so short batches never flash a dialog. loadWindow_ is rebuilt from scratch each time, so loadBar_/loadFileLabel_ are raw pointers that must be nulled in closeLoadWindow().
• Sources are held as an immutable shared_ptr<const SourceList> and edited copy-on-write via mutateSources(), so a render in flight can never race with an add/remove.

Image buffer

Image is tightly packed 8-bit RGB with stride exactly width * 3 — effects rely on this for memcpy, and GDK uploads the buffer as is. Decoding applies EXIF orientation. Image::load throws; loadImages collects per-file LoadFailures instead.

Reference

python-reference/ is the original Python prototype, kept only for comparison. Do not modify it or import from it.