Give Effector a version and a changelog, shown from the menu

The version is the project() line of CMakeLists.txt and nowhere else:
CMake writes it, with the text of CHANGELOG.md, into a generated
core/version.hpp, so the number and the release notes the binary shows
are the ones it was built from. effector --version (-V) prints it, and
the header-bar menu gains a section with Changelog, a window laying the
Markdown out as headings and bullets, and About Effector.

The core tests hold the newest changelog entry to the current version,
so a bump cannot go in without its notes. Releases are tagged vX.Y.Z;
this is 0.5.0, and the changelog reconstructs 0.1.0-0.4.0 from the
history.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -0,0 +1,73 @@
+# Changelog
+
+Every release of Effector, newest first. The version lives in one place, the
+`project()` line of `CMakeLists.txt`, and each release is a `vX.Y.Z` tag on the
+commit that made it. The interface shows this file under Changelog in its menu.
+
+## [0.5.0] - 2026-09-26
+
+### Added
+- A version number: `effector --version` prints it, and About Effector in the
+  menu shows it.
+- This changelog, readable from the interface under Changelog in the menu.
+- Open Recent in the project menu, listing the projects opened or saved here.
+- An optional shadow or glow under the image overlay, with an offset, size,
+  spread, colour and opacity.
+- Reordering the chain by dragging a row.
+
+### Fixed
+- The params' scrollbar no longer covers the spin buttons.
+
+## [0.4.0] - 2026-09-23
+
+### Added
+- Eight chaotic effects: slit shift, channel split, pixel sort, corruption,
+  shatter, warp, bit crush and feedback. None needs sources, so any of them can
+  lead a chain.
+- The sidebar split into Chain and Setup tabs.
+- A rotation for the text effect's placement.
+- Text stages labelled in the chain list with their words.
+
+### Changed
+- The preview stays centred however long the status line gets.
+- The status line stays short, with the full chain and setup in its tooltip.
+- The chain/params split fits the chain's rows until it is dragged; a
+  double-click on the handle fits it again.
+- The mouse wheel scrolls past spin buttons that do not have the focus.
+
+## [0.3.0] - 2026-09-19
+
+### Added
+- Named styles: several text stages can share one font and colour, and editing
+  the style moves every stage that follows it.
+- Switching a chain stage off without taking it apart, in the interface and
+  with `--disable NAME` on the command line.
+
+### Changed
+- The interface opens on an empty chain, and shows the sources only when the
+  chain uses them.
+
+## [0.2.0] - 2026-09-18
+
+### Added
+- Effect chains: stages cascade, each handed the previous one's output, built in
+  the sidebar or with repeated `-e`.
+- Blur, film grain, black and white, image overlay, text and tiles effects.
+- Projects saved and opened as plain JSON.
+- Standard web and print canvas formats (`--format`, `--dpi`).
+- Effects declare whether they need source images, so a chain led by blur
+  renders with none loaded.
+
+### Changed
+- The chain comes first in the sidebar.
+
+### Fixed
+- The canvas size is checked before it is narrowed to an int.
+- Projects are written and read in the C locale, and keep the seed whole.
+
+## [0.1.0] - 2026-09-18
+
+### Added
+- The C++20 port of the Python prototype: a GTK 4 interface and a headless
+  command line over pluggable effects, starting with scanlines.
+- Source images load in the background, with a progress window and Cancel.

CLAUDE.md

@@ -12,7 +12,7 @@ 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
+The core 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
@@ -20,12 +20,33 @@ 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.
 
+The interface has its own binary, `./build/tests/effector_gui_tests`
+(`tests/gui_tests.cpp`, same `check()` style), which opens the real window and
+drives it by widget names and tooltips (`chain-list`, `add-effect`,
+`sources`, "Move up", ...). It needs a display: ctest runs it under `xvfb-run`
+when that is installed and otherwise reports it skipped (exit 77). To run it by
+hand, use the Xvfb invocation below.
+
 Headless render (no display needed, the fastest end-to-end smoke test):
 
 ```bash
 build/effector -o /tmp/out.png -s 800x600 --strip-height 6 --seed 1 a.jpg b.png
 ```
 
+### Versions and the changelog
+
+The version is the `project()` line of `CMakeLists.txt`, and nowhere else.
+CMake writes it, together with the text of `CHANGELOG.md`, into a generated
+`core/version.hpp` (`kVersion`, `kChangelog`, from `src/core/version.hpp.in`)
+in the build tree. `--version` prints it, and the header-bar menu shows it
+under About Effector and the changelog under Changelog. The `version` core test
+fails unless the newest `## [X.Y.Z]` entry in `CHANGELOG.md` is the current
+version, so a bump and its changelog entry go in together. Each release is an
+annotated `vX.Y.Z` tag on the commit that made it. When you add a user-visible
+change, add a line to the newest changelog entry, or start a new entry if that
+one is already tagged. The Changelog window reads only headings, `- ` bullets
+(wrapped onto indented lines) and `` `code` ``, so keep the file to those.
+
 ### Running the GUI from this shell
 
 GTK picks Wayland from an inherited `WAYLAND_DISPLAY` and will not draw into an
@@ -53,6 +74,17 @@ travel as `ParamValues` (a
 `map<string, variant<long,double,bool,string>>`), read back with
 `paramInt`/`paramDouble`/`paramBool`/`paramChoice`.
 
+A param can also be marked `.styled()`, which says a *named style* carries it
+rather than the stage it sits on: the font and the colour of a text stage, but
+never its words or its placement. The pool a style comes from is named by
+`Effect::styleKind()` (empty by default — the effect takes no style; `"text"`
+for the text effect), and effects answering the same kind share one pool, so a
+second text-ish effect would slot into the styles that already exist. The
+front-ends know nothing more than that: the interface builds the style row and
+the project file writes a style's params from `styleSpecs(kind)`
+(`src/core/style.cpp`), which is to a style exactly what `params()` is to a
+stage.
+
 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`)
@@ -73,10 +105,32 @@ 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.
+
+### A style is a look several stages share
+
+`ChainStage::style` names a style, and `stageValues` (`src/core/chain.cpp`) is
+the one place that resolves one: an effect's defaults, then the stage's own
+values, then the style's values for the params it carries. A stage always keeps
+a full set of values of its own beside the style, so switching it to "Custom",
+dropping the style, or opening the project in a build that does not know the
+style renders exactly the same picture — a style moves stages together, it
+never holds the only copy of anything. The interface writes an edited param to
+both the style and the stage for that reason. `renderChain` takes the pool as a
+trailing argument; the command line builds no styles and passes none.
+
 The interface builds the chain in the sidebar ("Effect chain": add from the
-menu, reorder, remove, 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`. Flags share one namespace across all effects, so `buildChain`
+menu, reorder by dragging a row or with its arrows, 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.
 
@@ -94,25 +148,33 @@ 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, canvas and seed — as a small JSON file, with its own
+named styles, the chain with its params (and its `"enabled": false` and
+`"style"`, each written only when there is something to say), canvas and seed — as a small JSON file, with its own
 minimal reader rather than a JSON dependency. Writing is driven by the effects'
 `ParamSpec`s, 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.
+project keeps the defaults for params that did not exist when it was saved. The
+same leniency covers styles: one of a kind this build does not know, one with
+no name or a repeated one, and a stage naming a style the file does not hold
+are each dropped on their own rather than refusing the project.
 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
+the project name. Open Recent lists the projects opened or saved here, kept in
+GTK's shared `RecentManager` list and told apart from other programs' files by
+the `effector` application name on each entry; the GUI tests point
+`XDG_DATA_HOME` at a temporary folder so they never touch the user's list. 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
+no display) + Threads — **no gtkmm, no display**. `effector_gui` (static) adds
+`src/cli/` and `src/gui/` and links gtkmm, and the `effector` executable is
+`src/main.cpp` on top of it; the GUI tests link `effector_gui` too. Keep GTK out of
 `src/core/` and `src/effects/`; the tests link the core alone and rely on this.
 
 ### Determinism is a contract

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.20)
-project(effector VERSION 0.1.0 LANGUAGES CXX)
+project(effector VERSION 0.5.0 LANGUAGES CXX)
 
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
@@ -21,6 +21,14 @@ pkg_check_modules(PANGOCAIRO REQUIRED IMPORTED_TARGET pangocairo)
 
 find_package(Threads REQUIRED)
 
+# --- version: the one number, and the changelog that goes with it ------------
+# The version is the project() line above; each release is a vX.Y.Z tag on the
+# commit that set it. CHANGELOG.md is baked in so the interface can show it,
+# and editing it re-runs the configure step.
+file(READ ${CMAKE_CURRENT_SOURCE_DIR}/CHANGELOG.md EFFECTOR_CHANGELOG)
+set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS CHANGELOG.md)
+configure_file(src/core/version.hpp.in ${CMAKE_CURRENT_BINARY_DIR}/generated/core/version.hpp @ONLY)
+
 # --- core: effects and image handling, no GUI ---------------------------------
 add_library(effector_core STATIC
     src/core/canvas.cpp
@@ -31,28 +39,41 @@ add_library(effector_core STATIC
     src/core/project.cpp
     src/core/registry.cpp
     src/core/rng.cpp
+    src/core/style.cpp
+    src/effects/bitcrush.cpp
     src/effects/blur.cpp
+    src/effects/channelsplit.cpp
+    src/effects/corrupt.cpp
+    src/effects/feedback.cpp
     src/effects/grain.cpp
     src/effects/monochrome.cpp
     src/effects/overlay.cpp
+    src/effects/pixelsort.cpp
     src/effects/scanlines.cpp
+    src/effects/shatter.cpp
+    src/effects/slitshift.cpp
     src/effects/text.cpp
     src/effects/tiles.cpp
+    src/effects/warp.cpp
 )
-target_include_directories(effector_core PUBLIC src)
+target_include_directories(effector_core PUBLIC src ${CMAKE_CURRENT_BINARY_DIR}/generated)
 # The core is GUI-free: it only needs gdk-pixbuf for decoding and encoding,
 # so headless rendering works without a display.
 target_link_libraries(effector_core PUBLIC PkgConfig::GDKPIXBUF PkgConfig::PANGOCAIRO Threads::Threads)
 target_compile_options(effector_core PRIVATE -Wall -Wextra -Wpedantic)
 
-# --- application --------------------------------------------------------------
-add_executable(effector
-    src/main.cpp
+# --- interface: the GTK window, split out so the GUI tests can link it --------
+add_library(effector_gui STATIC
     src/cli/options.cpp
     src/gui/app.cpp
     src/gui/window.cpp
 )
-target_link_libraries(effector PRIVATE effector_core PkgConfig::GTKMM)
+target_link_libraries(effector_gui PUBLIC effector_core PkgConfig::GTKMM)
+target_compile_options(effector_gui PRIVATE -Wall -Wextra -Wpedantic)
+
+# --- application --------------------------------------------------------------
+add_executable(effector src/main.cpp)
+target_link_libraries(effector PRIVATE effector_gui)
 target_compile_options(effector PRIVATE -Wall -Wextra -Wpedantic)
 
 install(TARGETS effector RUNTIME DESTINATION bin)

README.md

@@ -25,6 +25,7 @@ installs it to `~/.local/bin`.
 build/effector                  # GTK interface
 build/effector --list-effects
 build/effector --help
+build/effector --version
 ```
 
 Headless rendering, no display needed:
@@ -60,6 +61,17 @@ batch. Small batches finish before the window would be drawn, so it only appears
 if the decode is still going after 250 ms. On a terminal the headless mode keeps
 a single `reading n/total` line updated on stderr; redirected output stays clean.
 
+## Versions
+
+Releases are listed in [CHANGELOG.md](CHANGELOG.md) and tagged `vX.Y.Z`
+(`git tag -l 'v*'`). `effector --version` prints the version, and the menu in
+the interface has Changelog and About Effector.
+
+To cut a release: bump the `project()` version in `CMakeLists.txt`, move the
+changes into a new `## [X.Y.Z] - date` entry at the top of `CHANGELOG.md` (the
+core tests fail until the two agree), commit, and tag it:
+`git tag -a vX.Y.Z -m "Effector X.Y.Z"`.
+
 ## Effects
 
 ### scanlines

src/cli/options.cpp

@@ -1,5 +1,6 @@
 #include "cli/options.hpp"
 
+#include <algorithm>
 #include <charconv>
 #include <cstdint>
 #include <cstring>
@@ -60,6 +61,8 @@ Options parseOptions(int argc, char** argv) {
 
         if (arg == "-h" || arg == "--help") {
             options.showHelp = true;
+        } else if (arg == "-V" || arg == "--version") {
+            options.showVersion = true;
         } else if (arg == "--list-effects") {
             options.listEffects = true;
         } else if (arg == "-e" || arg == "--effect") {
@@ -89,6 +92,10 @@ Options parseOptions(int argc, char** argv) {
                                   std::to_string(kMinDpi) + "-" + std::to_string(kMaxDpi));
             }
             options.dpi = static_cast<int>(dpi);
+        } else if (arg == "--disable") {
+            const std::string name = requireValue(argc, argv, i, arg);
+            effectByName(name);  // validate now, exactly as -e does
+            options.disabled.push_back(name);
         } else if (arg == "--seed") {
             const std::string value = requireValue(argc, argv, i, arg);
             long seed = 0;
@@ -160,7 +167,6 @@ Options parseOptions(int argc, char** argv) {
     if (const auto* format = canvasFormatByKey(options.format)) {
         canvasFormatSize(*format, options.dpi, options.width, options.height);
     }
-    if (options.effects.empty()) options.effects.push_back(defaultEffectName());
     return options;
 }
 
@@ -169,15 +175,18 @@ std::string usage(const char* programName) {
     out << "Usage: " << programName << " [options] [image ...]\n\n"
         << "Image effects app. Runs the GTK interface unless --output is given.\n\n"
         << "Options:\n"
-        << "  -e, --effect NAME     effect to apply, repeat to cascade (default: " << defaultEffectName() << ")\n"
+        << "  -e, --effect NAME     effect to apply, repeat to cascade (--output"
+           " defaults to " << defaultEffectName() << ")\n"
         << "  -o, --output FILE     render headlessly to this file and exit\n"
         << "  -s, --size WxH        canvas size, each side " << kMinCanvasSide << "-"
         << kMaxCanvasSide << " (default: 1920x1080)\n"
         << "      --format NAME     canvas format, overrides --size (see below)\n"
         << "      --dpi N           resolution of a print format, " << kMinDpi << "-" << kMaxDpi
         << " (default: " << kDefaultDpi << ")\n"
+        << "      --disable NAME    keep this effect in the chain but skip it\n"
         << "      --seed N          random seed (default: random)\n"
         << "      --list-effects    list available effects and exit\n"
+        << "  -V, --version         show the version and exit\n"
         << "  -h, --help            show this help and exit\n";
 
     out << "\nCanvas formats (--format):\n";
@@ -207,6 +216,8 @@ std::vector<ChainStage> buildChain(const Options& options) {
         ChainStage stage;
         stage.effect = effectByName(name);
         stage.values = stage.effect->defaults();
+        stage.enabled = std::find(options.disabled.begin(), options.disabled.end(), name) ==
+                        options.disabled.end();
         for (const auto& spec : stage.effect->params()) {
             const auto it = options.params.find(spec.key);
             if (it != options.params.end()) stage.values[spec.key] = it->second;

src/cli/options.hpp

@@ -14,6 +14,10 @@ namespace effector {
 struct Options {
     std::vector<std::string> images;
     std::vector<std::string> effects;  // one per cascade stage, in order
+    // The effects named by --disable: their stages stay in the chain, in
+    // place, but are skipped. Named rather than numbered, exactly as the
+    // params are, so two stages of one effect are disabled together.
+    std::vector<std::string> disabled;
     std::string output;              // empty -> launch the interface
     int width = 1920;
     int height = 1080;
@@ -23,6 +27,7 @@ struct Options {
     ParamValues params;              // only the keys the user actually passed
     bool listEffects = false;
     bool showHelp = false;
+    bool showVersion = false;
 };
 
 // Throws EffectError on bad input. Effect flags are generated from the
@@ -33,7 +38,8 @@ std::string usage(const char* programName);
 
 // Turns the parsed names and flags into cascade stages: every flag goes to the
 // stage whose effect declares it, so --strip-height and --radius can be given
-// together for `-e scanlines -e blur`.
+// together for `-e scanlines -e blur`. A stage named by --disable is built
+// with all its settings and marked to be skipped.
 std::vector<ChainStage> buildChain(const Options& options);
 
 }  // namespace effector

src/core/chain.cpp

@@ -2,17 +2,51 @@
 
 namespace effector {
 
+std::vector<const ChainStage*> enabledStages(const std::vector<ChainStage>& stages) {
+    std::vector<const ChainStage*> running;
+    running.reserve(stages.size());
+    for (const auto& stage : stages) {
+        if (stage.enabled && stage.effect) running.push_back(&stage);
+    }
+    return running;
+}
+
+ParamValues stageValues(const ChainStage& stage, const StyleSet& styles) {
+    ParamValues values = stage.effect->defaults();
+    for (const auto& [key, value] : stage.values) values[key] = value;
+
+    const Style* style = findStyle(styles, stage.effect->styleKind(), stage.style);
+    if (style != nullptr) {
+        // Only the params the effect marked styled(): the words and the
+        // placement stay the stage's own, which is what lets two stages share
+        // one look without sharing a position.
+        for (const auto& spec : stage.effect->params()) {
+            if (!spec.inStyle) continue;
+            const auto found = style->values.find(spec.key);
+            if (found != style->values.end()) values[spec.key] = found->second;
+        }
+    }
+    return values;
+}
+
 Image renderChain(const std::vector<ChainStage>& stages, const std::vector<Image>& sources,
-                  int width, int height, Rng& rng) {
+                  int width, int height, Rng& rng, const StyleSet& styles) {
     if (stages.empty()) throw EffectError("The effect chain is empty.");
+    for (const auto& stage : stages) {
+        if (!stage.effect) throw EffectError("The effect chain has an empty stage.");
+    }
+
+    // A disabled stage never reaches the render at all: it is not handed an
+    // image and draws nothing from the shared rng, so switching one off gives
+    // back exactly the picture the chain made before it was added.
+    const auto running = enabledStages(stages);
+    if (running.empty()) throw EffectError("Every effect in the chain is disabled.");
 
     Image image;
-    for (std::size_t i = 0; i < stages.size(); ++i) {
-        const auto& stage = stages[i];
-        if (!stage.effect) throw EffectError("The effect chain has an empty stage.");
+    for (std::size_t i = 0; i < running.size(); ++i) {
+        const auto& stage = *running[i];
 
-        auto values = stage.effect->defaults();
-        for (const auto& [key, value] : stage.values) values[key] = value;
+        const auto values = stageValues(stage, styles);
 
         if (i == 0) {
             image = stage.effect->render(sources, width, height, rng, values);
@@ -27,26 +61,25 @@ Image renderChain(const std::vector<ChainStage>& stages, const std::vector<Image
 }
 
 bool chainNeedsSources(const std::vector<ChainStage>& stages) {
-    if (stages.empty() || !stages.front().effect) return false;
-    return stages.front().effect->needsSources();
+    const auto running = enabledStages(stages);
+    if (running.empty()) return false;
+    return running.front()->effect->needsSources();
 }
 
 std::string chainTitle(const std::vector<ChainStage>& stages) {
     std::string text;
-    for (const auto& stage : stages) {
-        if (!stage.effect) continue;
+    for (const auto* stage : enabledStages(stages)) {
         if (!text.empty()) text += " → ";
-        text += stage.effect->title();
+        text += stage->effect->title();
     }
     return text;
 }
 
 std::string chainSlug(const std::vector<ChainStage>& stages) {
     std::string text;
-    for (const auto& stage : stages) {
-        if (!stage.effect) continue;
+    for (const auto* stage : enabledStages(stages)) {
         if (!text.empty()) text += "-";
-        text += stage.effect->name();
+        text += stage->effect->name();
     }
     return text;
 }

src/core/chain.hpp

@@ -7,6 +7,7 @@
 #include "core/image.hpp"
 #include "core/params.hpp"
 #include "core/rng.hpp"
+#include "core/style.hpp"
 
 namespace effector {
 
@@ -21,23 +22,46 @@ inline constexpr int kMaxCanvasSide = 20000;
 struct ChainStage {
     EffectPtr effect;
     ParamValues values;  // missing keys fall back to the effect's defaults
+    // A disabled stage is skipped whole, keeping its settings and its place in
+    // the chain, so a stage can be switched off and back on while trying
+    // things out without being taken apart and rebuilt.
+    bool enabled = true;
+    // The style this stage follows, by name, in the pool its effect names with
+    // styleKind(); empty when the stage stands on its own. A stage keeps a
+    // full set of values either way, so a style that is dropped or renamed
+    // away leaves the stage rendering exactly what it rendered before.
+    std::string style = {};
 };
 
-// Renders the stages in order. The first one sees the loaded sources; every
-// later one sees the previous stage's output as its only source, so blur after
-// scanlines softens the scanlines rather than the photographs.
+// The values a stage actually runs with: its effect's defaults, then the
+// stage's own values, then the values of the style it follows for the params
+// that style carries. The one place a style is resolved.
+ParamValues stageValues(const ChainStage& stage, const StyleSet& styles);
+
+// The stages that actually run, in order, as pointers into `stages`. A
+// disabled stage draws nothing from the rng and is handed no image, so a chain
+// renders exactly as it would if that stage had never been added -- this is
+// the one place the rest of the code asks what "disabled" means.
+std::vector<const ChainStage*> enabledStages(const std::vector<ChainStage>& stages);
+
+// Renders the enabled stages in order. The first one sees the loaded sources;
+// every later one sees the previous stage's output as its only source, so blur
+// after scanlines softens the scanlines rather than the photographs.
 //
 // All stages share one Rng and run strictly in sequence, so a seed still
-// reproduces the cascade byte for byte.
+// reproduces the cascade byte for byte. Throws when no stage is left to run.
+// `styles` is the project's pool; a chain built without one -- the command
+// line's -- passes none and renders from the stages alone.
 Image renderChain(const std::vector<ChainStage>& stages, const std::vector<Image>& sources,
-                  int width, int height, Rng& rng);
+                  int width, int height, Rng& rng, const StyleSet& styles = {});
 
-// Whether the chain has to be given source images. Only the first stage ever
-// sees them — every later one works on the stage before it — so this is simply
-// whether the first effect declares that it needs them.
+// Whether the chain has to be given source images. Only the first stage that
+// runs ever sees them — every later one works on the stage before it — so this
+// is simply whether that effect declares that it needs them.
 bool chainNeedsSources(const std::vector<ChainStage>& stages);
 
-// "Scanlines → Blur", for window titles and status lines.
+// "Scanlines → Blur", for window titles and status lines. Both of these name
+// what was rendered, so a disabled stage is left out of them.
 std::string chainTitle(const std::vector<ChainStage>& stages);
 
 // "scanlines-blur", for file names.

src/core/effect.cpp

@@ -4,25 +4,7 @@ namespace effector {
 
 ParamValues Effect::defaults() const {
     ParamValues values;
-    for (const auto& spec : params()) {
-        switch (spec.type) {
-            case ParamSpec::Type::Int:
-                values[spec.key] = static_cast<long>(spec.defaultValue);
-                break;
-            case ParamSpec::Type::Double:
-                values[spec.key] = spec.defaultValue;
-                break;
-            case ParamSpec::Type::Bool:
-                values[spec.key] = spec.defaultValue != 0.0;
-                break;
-            case ParamSpec::Type::Choice:
-            case ParamSpec::Type::Path:
-            case ParamSpec::Type::Text:
-            case ParamSpec::Type::Color:
-                values[spec.key] = spec.defaultChoice;
-                break;
-        }
-    }
+    for (const auto& spec : params()) values[spec.key] = paramDefault(spec);
     return values;
 }
 

src/core/effect.hpp

@@ -32,6 +32,19 @@ public:
     // chain that starts with one of them needs no sources at all.
     virtual bool needsSources() const { return true; }
 
+    // The pool of named styles this effect's styled params are drawn from, or
+    // empty when it takes no style. Effects that answer the same kind share
+    // one pool, so a stage can be pointed at a look its neighbours already
+    // use. An effect with no kind must declare no styled params.
+    virtual std::string styleKind() const { return {}; }
+
+    // How a stage of this effect is named in a list of stages, given its
+    // values: the title unless the values say something more telling.
+    virtual std::string label(const ParamValues& values) const {
+        (void)values;
+        return title();
+    }
+
     virtual Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
                          const ParamValues& values) const = 0;
 

src/core/params.cpp

@@ -10,6 +10,12 @@ std::string ParamSpec::flag() const {
     return flag;
 }
 
+ParamSpec ParamSpec::styled() const {
+    ParamSpec copy = *this;
+    copy.inStyle = true;
+    return copy;
+}
+
 ParamSpec ParamSpec::makeInt(std::string key, std::string label, long defaultValue, long minimum,
                              long maximum, std::string help, long step) {
     ParamSpec spec;
@@ -103,6 +109,23 @@ const ParamValue* find(const ParamValues& values, const std::string& key) {
 
 }  // namespace
 
+ParamValue paramDefault(const ParamSpec& spec) {
+    switch (spec.type) {
+        case ParamSpec::Type::Int:
+            return static_cast<long>(spec.defaultValue);
+        case ParamSpec::Type::Double:
+            return spec.defaultValue;
+        case ParamSpec::Type::Bool:
+            return spec.defaultValue != 0.0;
+        case ParamSpec::Type::Choice:
+        case ParamSpec::Type::Path:
+        case ParamSpec::Type::Text:
+        case ParamSpec::Type::Color:
+            break;
+    }
+    return spec.defaultChoice;
+}
+
 long paramInt(const ParamValues& values, const std::string& key, long fallback) {
     if (const auto* value = find(values, key)) {
         if (const auto* v = std::get_if<long>(value)) return *v;

src/core/params.hpp

@@ -24,9 +24,17 @@ struct ParamSpec {
     int digits = 2;
     std::string defaultChoice;
     std::vector<std::string> choices;
+    // Whether a named style carries this param rather than the stage it sits
+    // on: see core/style.hpp.
+    bool inStyle = false;
 
     std::string flag() const;  // "strip_height" -> "--strip-height"
 
+    // A copy of this spec marked as carried by a style, so that a declaration
+    // reads makeDouble("font_size", ...).styled() and the factories keep the
+    // signatures they have.
+    ParamSpec styled() const;
+
     static ParamSpec makeInt(std::string key, std::string label, long defaultValue, long minimum,
                              long maximum, std::string help = {}, long step = 1);
     static ParamSpec makeDouble(std::string key, std::string label, double defaultValue,
@@ -53,6 +61,10 @@ struct ParamSpec {
 using ParamValue = std::variant<long, double, bool, std::string>;
 using ParamValues = std::map<std::string, ParamValue>;
 
+// The value a spec stands for when nothing has been set: one place, so that
+// an effect's defaults and a style's are filled the same way.
+ParamValue paramDefault(const ParamSpec& spec);
+
 long paramInt(const ParamValues& values, const std::string& key, long fallback);
 double paramDouble(const ParamValues& values, const std::string& key, double fallback);
 bool paramBool(const ParamValues& values, const std::string& key, bool fallback);

src/core/project.cpp

@@ -325,6 +325,96 @@ std::string resolve(const std::string& path, const std::string& directory) {
     return (std::filesystem::path(directory) / file).lexically_normal().string();
 }
 
+// The params of a stage or of a style, written from the specs rather than from
+// whatever the values happen to hold: a key the effect does not declare is
+// never written, so it can never be read back either.
+void writeParams(std::ostream& out, const std::vector<ParamSpec>& specs, const ParamValues& values,
+                 const std::string& directory) {
+    out << "{";
+    bool first = true;
+    for (const auto& spec : specs) {
+        out << (first ? "\n" : ",\n") << "        " << quote(spec.key) << ": ";
+        first = false;
+        switch (spec.type) {
+            case ParamSpec::Type::Bool:
+                out << (paramBool(values, spec.key, spec.defaultValue != 0.0) ? "true" : "false");
+                break;
+            case ParamSpec::Type::Int:
+                out << paramInt(values, spec.key, static_cast<long>(spec.defaultValue));
+                break;
+            case ParamSpec::Type::Double:
+                out << number(paramDouble(values, spec.key, spec.defaultValue), spec.digits);
+                break;
+            case ParamSpec::Type::Choice:
+            case ParamSpec::Type::Text:
+                out << quote(paramText(values, spec.key, spec.defaultChoice));
+                break;
+            case ParamSpec::Type::Color: {
+                std::uint8_t rgb[3];
+                paramColor(values, spec.key, spec.defaultChoice, rgb);
+                out << quote(formatColor(rgb));
+                break;
+            }
+            case ParamSpec::Type::Path: {
+                // Written relative to the project folder, exactly as the
+                // sources are, so a folder still opens once it is moved.
+                const auto path = paramText(values, spec.key, "");
+                out << quote(path.empty() ? path : relativeTo(path, directory));
+                break;
+            }
+        }
+    }
+    out << (specs.empty() ? "}" : "\n      }");
+}
+
+// The mirror image: only declared keys are read, each behind the gate its type
+// asks for, so anything else in the file leaves the default standing.
+void readParams(const std::vector<ParamSpec>& specs, const Json& params,
+                const std::string& directory, ParamValues& values) {
+    for (const auto& spec : specs) {
+        const auto* value = params.member(spec.key);
+        if (value == nullptr) continue;
+        switch (spec.type) {
+            case ParamSpec::Type::Bool:
+                if (value->kind == Json::Kind::Bool) values[spec.key] = value->boolean;
+                break;
+            case ParamSpec::Type::Int:
+                if (value->kind == Json::Kind::Number) {
+                    values[spec.key] = static_cast<long>(std::llround(value->number));
+                }
+                break;
+            case ParamSpec::Type::Double:
+                if (value->kind == Json::Kind::Number) values[spec.key] = value->number;
+                break;
+            case ParamSpec::Type::Path:
+                if (value->kind == Json::Kind::String) {
+                    values[spec.key] =
+                        value->text.empty() ? value->text : resolve(value->text, directory);
+                }
+                break;
+            case ParamSpec::Type::Text:
+                if (value->kind == Json::Kind::String) values[spec.key] = value->text;
+                break;
+            case ParamSpec::Type::Color: {
+                // A colour that does not parse keeps the default, exactly as
+                // an unknown choice does.
+                std::uint8_t rgb[3];
+                if (value->kind == Json::Kind::String && parseColor(value->text, rgb)) {
+                    values[spec.key] = formatColor(rgb);
+                }
+                break;
+            }
+            case ParamSpec::Type::Choice:
+                for (const auto& choice : spec.choices) {
+                    if (value->kind == Json::Kind::String && value->text == choice) {
+                        values[spec.key] = choice;
+                    }
+                }
+                break;
+        }
+    }
+}
+
 }  // namespace
 
 std::string projectToJson(const Project& project, const std::string& directory) {
@@ -353,51 +443,37 @@ std::string projectToJson(const Project& project, const std::string& directory)
     }
     out << (project.sources.empty() ? "" : "\n  ") << "],\n";
 
+    // Before the chain, because a stage's "style" is a name from this list.
+    if (!project.styles.empty()) {
+        out << "  \"styles\": [";
+        for (std::size_t i = 0; i < project.styles.size(); ++i) {
+            const auto& style = project.styles[i];
+            out << (i == 0 ? "\n" : ",\n");
+            out << "    {\n      \"kind\": " << quote(style.kind) << ",\n";
+            out << "      \"name\": " << quote(style.name) << ",\n";
+            out << "      \"params\": ";
+            writeParams(out, styleSpecs(style.kind), style.values, directory);
+            out << "\n    }";
+        }
+        out << "\n  ],\n";
+    }
+
     out << "  \"chain\": [";
     for (std::size_t i = 0; i < project.stages.size(); ++i) {
         const auto& stage = project.stages[i];
         if (!stage.effect) continue;
         out << (i == 0 ? "\n" : ",\n");
         out << "    {\n      \"effect\": " << quote(stage.effect->name()) << ",\n";
-        out << "      \"params\": {";
-
-        const auto& specs = stage.effect->params();
-        bool first = true;
-        for (const auto& spec : specs) {
-            out << (first ? "\n" : ",\n") << "        " << quote(spec.key) << ": ";
-            first = false;
-            switch (spec.type) {
-                case ParamSpec::Type::Bool:
-                    out << (paramBool(stage.values, spec.key, spec.defaultValue != 0.0) ? "true"
-                                                                                       : "false");
-                    break;
-                case ParamSpec::Type::Int:
-                    out << paramInt(stage.values, spec.key, static_cast<long>(spec.defaultValue));
-                    break;
-                case ParamSpec::Type::Double:
-                    out << number(paramDouble(stage.values, spec.key, spec.defaultValue),
-                                  spec.digits);
-                    break;
-                case ParamSpec::Type::Choice:
-                case ParamSpec::Type::Text:
-                    out << quote(paramText(stage.values, spec.key, spec.defaultChoice));
-                    break;
-                case ParamSpec::Type::Color: {
-                    std::uint8_t rgb[3];
-                    paramColor(stage.values, spec.key, spec.defaultChoice, rgb);
-                    out << quote(formatColor(rgb));
-                    break;
-                }
-                case ParamSpec::Type::Path: {
-                    // Written relative to the project folder, exactly as the
-                    // sources are, so a folder still opens once it is moved.
-                    const auto path = paramText(stage.values, spec.key, "");
-                    out << quote(path.empty() ? path : relativeTo(path, directory));
-                    break;
-                }
-            }
-        }
-        out << (specs.empty() ? "}" : "\n      }") << "\n    }";
+        // Only written when it is false: a stage is enabled unless the file
+        // says otherwise, so an ordinary project stays as uncluttered as it
+        // was before a stage could be switched off at all.
+        if (!stage.enabled) out << "      \"enabled\": false,\n";
+        // Likewise only when there is one: a stage that stands on its own
+        // values says nothing about styles at all.
+        if (!stage.style.empty()) out << "      \"style\": " << quote(stage.style) << ",\n";
+        out << "      \"params\": ";
+        writeParams(out, stage.effect->params(), stage.values, directory);
+        out << "\n    }";
     }
     out << (project.stages.empty() ? "" : "\n  ") << "]\n";
     out << "}\n";
@@ -453,6 +529,33 @@ Project projectFromJson(const std::string& text, const std::string& directory) {
         }
     }
 
+    // Read before the chain, so that a stage's "style" can be checked against
+    // the pool as it is read.
+    if (const auto* styles = root.member("styles")) {
+        for (const auto& item : styles->items) {
+            const auto* kind = item.member("kind");
+            const auto* name = item.member("name");
+            if (kind == nullptr || kind->kind != Json::Kind::String) continue;
+            if (name == nullptr || name->kind != Json::Kind::String || name->text.empty()) continue;
+
+            // A kind no effect in this build claims carries no params, so
+            // there would be nothing to keep; a repeated name would make
+            // "style": "Title" ambiguous, so the first one wins.
+            const auto specs = styleSpecs(kind->text);
+            if (specs.empty()) continue;
+            if (findStyle(project.styles, kind->text, name->text) != nullptr) continue;
+
+            Style style;
+            style.kind = kind->text;
+            style.name = name->text;
+            style.values = styleDefaults(style.kind);
+            if (const auto* params = item.member("params")) {
+                readParams(specs, *params, directory, style.values);
+            }
+            project.styles.push_back(std::move(style));
+        }
+    }
+
     const auto* chain = root.member("chain");
     if (chain == nullptr || chain->kind != Json::Kind::Array || chain->items.empty()) {
         throw EffectError("the project has no effect chain");
@@ -466,53 +569,26 @@ Project projectFromJson(const std::string& text, const std::string& directory) {
         ChainStage stage;
         stage.effect = effectByName(name->text);  // throws on an unknown effect
         stage.values = stage.effect->defaults();
+        if (const auto* enabled = item.member("enabled");
+            enabled != nullptr && enabled->kind == Json::Kind::Bool) {
+            stage.enabled = enabled->boolean;
+        }
 
         // Driven by the specs, not by the file: a key the effect does not
         // declare is dropped, and an old project simply keeps the defaults for
         // params that did not exist when it was written.
         if (const auto* params = item.member("params")) {
-            for (const auto& spec : stage.effect->params()) {
-                const auto* value = params->member(spec.key);
-                if (value == nullptr) continue;
-                switch (spec.type) {
-                    case ParamSpec::Type::Bool:
-                        if (value->kind == Json::Kind::Bool) stage.values[spec.key] = value->boolean;
-                        break;
-                    case ParamSpec::Type::Int:
-                        if (value->kind == Json::Kind::Number) {
-                            stage.values[spec.key] = static_cast<long>(std::llround(value->number));
-                        }
-                        break;
-                    case ParamSpec::Type::Double:
-                        if (value->kind == Json::Kind::Number) stage.values[spec.key] = value->number;
-                        break;
-                    case ParamSpec::Type::Path:
-                        if (value->kind == Json::Kind::String) {
-                            stage.values[spec.key] =
-                                value->text.empty() ? value->text : resolve(value->text, directory);
-                        }
-                        break;
-                    case ParamSpec::Type::Text:
-                        if (value->kind == Json::Kind::String) stage.values[spec.key] = value->text;
-                        break;
-                    case ParamSpec::Type::Color: {
-                        // A colour that does not parse keeps the default,
-                        // exactly as an unknown choice does.
-                        std::uint8_t rgb[3];
-                        if (value->kind == Json::Kind::String && parseColor(value->text, rgb)) {
-                            stage.values[spec.key] = formatColor(rgb);
-                        }
-                        break;
-                    }
-                    case ParamSpec::Type::Choice:
-                        for (const auto& choice : spec.choices) {
-                            if (value->kind == Json::Kind::String && value->text == choice) {
-                                stage.values[spec.key] = choice;
-                            }
-                        }
-                        break;
-                }
+            readParams(stage.effect->params(), *params, directory, stage.values);
         }
+
+        // A style is kept only when the file actually holds one of that name
+        // for this effect's pool: a stage pointing at a style that is not
+        // there falls back to the values it wrote beside it, which are the
+        // ones it last rendered with.
+        if (const auto* style = item.member("style");
+            style != nullptr && style->kind == Json::Kind::String &&
+            findStyle(project.styles, stage.effect->styleKind(), style->text) != nullptr) {
+            stage.style = style->text;
         }
         project.stages.push_back(std::move(stage));
     }

src/core/project.hpp

@@ -8,6 +8,7 @@
 #include "core/canvas.hpp"
 #include "core/chain.hpp"
 #include "core/params.hpp"
+#include "core/style.hpp"
 
 namespace effector {
 
@@ -17,6 +18,10 @@ namespace effector {
 struct Project {
     std::vector<std::string> sources;  // absolute paths
     std::vector<ChainStage> stages;
+    // The named looks the stages draw their formatting from. Kept beside the
+    // chain rather than inside it because that is the whole point of a style:
+    // several stages share one, and editing it moves all of them at once.
+    StyleSet styles;
     int width = 1920;
     int height = 1080;
     // The named format the canvas came from, empty for a custom pixel size.
@@ -36,7 +41,9 @@ std::string projectToJson(const Project& project, const std::string& directory =
 
 // Throws EffectError on malformed JSON, an unknown effect or a missing chain.
 // Relative source paths are resolved against `directory`; params the effect
-// does not declare are dropped, and missing ones keep the effect's default.
+// does not declare are dropped, and missing ones keep the effect's default. A
+// style of an unknown kind, or a stage naming a style the file does not hold,
+// is dropped the same way: the stage keeps its own values and still renders.
 Project projectFromJson(const std::string& text, const std::string& directory = {});
 
 // Both throw EffectError: the file is the user's, so failures are reported

src/core/registry.cpp

@@ -1,12 +1,20 @@
 #include "core/registry.hpp"
 
+#include "effects/bitcrush.hpp"
 #include "effects/blur.hpp"
+#include "effects/channelsplit.hpp"
+#include "effects/corrupt.hpp"
+#include "effects/feedback.hpp"
 #include "effects/grain.hpp"
 #include "effects/monochrome.hpp"
 #include "effects/overlay.hpp"
+#include "effects/pixelsort.hpp"
 #include "effects/scanlines.hpp"
+#include "effects/shatter.hpp"
+#include "effects/slitshift.hpp"
 #include "effects/text.hpp"
 #include "effects/tiles.hpp"
+#include "effects/warp.hpp"
 
 namespace effector {
 
@@ -20,6 +28,14 @@ const std::vector<EffectPtr>& effects() {
         std::make_shared<OverlayEffect>(),
         std::make_shared<TextEffect>(),
         std::make_shared<TilesEffect>(),
+        std::make_shared<SlitShiftEffect>(),
+        std::make_shared<ChannelSplitEffect>(),
+        std::make_shared<PixelSortEffect>(),
+        std::make_shared<CorruptEffect>(),
+        std::make_shared<ShatterEffect>(),
+        std::make_shared<WarpEffect>(),
+        std::make_shared<BitCrushEffect>(),
+        std::make_shared<FeedbackEffect>(),
     };
     return registry;
 }

src/core/style.cpp

@@ -0,0 +1,39 @@
+#include "core/style.hpp"
+
+#include <algorithm>
+
+#include "core/registry.hpp"
+
+namespace effector {
+
+std::vector<ParamSpec> styleSpecs(const std::string& kind) {
+    std::vector<ParamSpec> specs;
+    if (kind.empty()) return specs;
+    for (const auto& effect : effects()) {
+        if (effect->styleKind() != kind) continue;
+        for (const auto& spec : effect->params()) {
+            if (!spec.inStyle) continue;
+            const bool known = std::any_of(specs.begin(), specs.end(), [&](const ParamSpec& seen) {
+                return seen.key == spec.key;
+            });
+            if (!known) specs.push_back(spec);
+        }
+    }
+    return specs;
+}
+
+ParamValues styleDefaults(const std::string& kind) {
+    ParamValues values;
+    for (const auto& spec : styleSpecs(kind)) values[spec.key] = paramDefault(spec);
+    return values;
+}
+
+const Style* findStyle(const StyleSet& styles, const std::string& kind, const std::string& name) {
+    if (kind.empty() || name.empty()) return nullptr;
+    for (const auto& style : styles) {
+        if (style.kind == kind && style.name == name) return &style;
+    }
+    return nullptr;
+}
+
+}  // namespace effector

src/core/style.hpp

@@ -0,0 +1,39 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+#include "core/params.hpp"
+
+namespace effector {
+
+// A named set of formatting values, shared by every stage that follows it.
+//
+// A style carries only the params an effect marked styled() -- the look, never
+// the placement -- so several text stages can share one typography while each
+// keeps its own words and its own corner of the canvas. Changing the style is
+// the point: it changes every stage pointing at it at once.
+struct Style {
+    std::string kind;    // the pool, as Effect::styleKind() names it
+    std::string name;    // unique within a kind, never empty
+    ParamValues values;  // the styled params only
+};
+
+using StyleSet = std::vector<Style>;
+
+// The styled specs of a kind: every registered effect answering that kind
+// contributes its styled params, the first declaration of a key winning. This
+// is to a style what Effect::params() is to a stage -- the only thing the
+// interface and the project file know about what a style holds -- so an empty
+// or unknown kind gives an empty list.
+std::vector<ParamSpec> styleSpecs(const std::string& kind);
+
+// A fresh set of values for a style of that kind: every styled param at the
+// default its effect declares, the way Effect::defaults() fills a stage.
+ParamValues styleDefaults(const std::string& kind);
+
+// The style of that name in that pool, or nullptr. A stage naming a style that
+// is not there simply stands on its own values.
+const Style* findStyle(const StyleSet& styles, const std::string& kind, const std::string& name);
+
+}  // namespace effector

src/core/version.hpp.in

@@ -0,0 +1,16 @@
+#pragma once
+
+// Generated by CMake from src/core/version.hpp.in; edit that, not the copy in
+// the build tree. The version comes from the project() line of CMakeLists.txt
+// and the changelog from CHANGELOG.md, both read at configure time.
+
+#include <string_view>
+
+namespace effector {
+
+inline constexpr std::string_view kVersion = "@PROJECT_VERSION@";
+
+// CHANGELOG.md as it stood when the build was configured, as Markdown.
+inline constexpr std::string_view kChangelog = R"changelog(@EFFECTOR_CHANGELOG@)changelog";
+
+}  // namespace effector

src/effects/bitcrush.cpp

@@ -0,0 +1,129 @@
+#include "effects/bitcrush.hpp"
+
+#include <algorithm>
+#include <array>
+#include <vector>
+
+#include "core/parallel.hpp"
+#include "effects/sampling.hpp"
+#include "effects/source_fill.hpp"
+
+namespace effector {
+
+const std::vector<ParamSpec>& BitCrushEffect::params() const {
+    static const std::vector<ParamSpec> specs = {
+        ParamSpec::makeChoice("crush_op", "Operation", "mixed",
+                              {"mixed", "posterize", "xor", "bitrotate", "channel_swap"},
+                              "posterize drops the low bits, xor flips random low bits, "
+                              "bitrotate turns each byte's bits round, channel_swap shuffles "
+                              "red, green and blue; mixed picks one for every band."),
+        ParamSpec::makeInt("crush_bits", "Bits", 3, 1, 7,
+                           "How many bits the operation reaches: dropped by posterize, flipped "
+                           "at most by xor, turned at most by bitrotate."),
+        ParamSpec::makeDouble("crush_coverage", "Coverage", 0.5, 0.0, 1.0,
+                              "Chance of each band being crushed."),
+        ParamSpec::makeInt("crush_band_height", "Band height", 32, 1, 4096,
+                           "Thickness in pixels of each band."),
+    };
+    return specs;
+}
+
+namespace {
+
+enum class Op : std::uint8_t { None, Posterize, Xor, Rotate, Swap };
+
+struct Band {
+    Op op = Op::None;
+    int rotate = 0;
+    std::array<std::uint8_t, 3> mask{};
+    std::array<int, 3> order{0, 1, 2};
+};
+
+Op opNamed(const std::string& name) {
+    if (name == "posterize") return Op::Posterize;
+    if (name == "xor") return Op::Xor;
+    if (name == "bitrotate") return Op::Rotate;
+    if (name == "channel_swap") return Op::Swap;
+    return Op::None;  // mixed: drawn per band
+}
+
+}  // namespace
+
+Image BitCrushEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                             const ParamValues& values) const {
+    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
+
+    const Op fixed = opNamed(paramChoice(values, "crush_op", "mixed"));
+    const int bits = static_cast<int>(std::clamp(paramInt(values, "crush_bits", 3), 1L, 7L));
+    const double coverage = std::clamp(paramDouble(values, "crush_coverage", 0.5), 0.0, 1.0);
+    const int bandHeight = static_cast<int>(std::max(1L, paramInt(values, "crush_band_height", 32)));
+
+    Image canvas = canvasFromSources(sources, width, height, rng);
+
+    const int bandCount = (height + bandHeight - 1) / bandHeight;
+    std::vector<Band> plan(static_cast<std::size_t>(bandCount));
+    for (auto& band : plan) {
+        if (!chance(rng.next(), coverage)) continue;
+        band.op = fixed != Op::None ? fixed : static_cast<Op>(1 + rng.below(3));
+        switch (band.op) {
+            case Op::Xor:
+                for (auto& mask : band.mask) {
+                    mask = static_cast<std::uint8_t>(rng.inRange(1, (1L << bits) - 1));
+                }
+                break;
+            case Op::Rotate:
+                band.rotate = static_cast<int>(rng.inRange(1, bits));
+                break;
+            case Op::Swap:
+                // Fisher-Yates, never leaving the order as it was.
+                do {
+                    band.order = {0, 1, 2};
+                    for (int i = 2; i > 0; --i) {
+                        std::swap(band.order[static_cast<std::size_t>(i)],
+                                  band.order[rng.below(static_cast<std::uint64_t>(i))]);
+                    }
+                } while (band.order[0] == 0 && band.order[1] == 1);
+                break;
+            default:
+                break;
+        }
+    }
+
+    const std::uint8_t keep = static_cast<std::uint8_t>(0xFF << bits);
+
+    parallelFor(static_cast<std::size_t>(height), [&](std::size_t begin, std::size_t end) {
+        for (std::size_t y = begin; y < end; ++y) {
+            const Band& band = plan[y / static_cast<std::size_t>(bandHeight)];
+            if (band.op == Op::None) continue;
+            std::uint8_t* row = canvas.row(static_cast<int>(y));
+            for (int x = 0; x < width; ++x) {
+                std::uint8_t* px = row + static_cast<std::size_t>(x) * 3;
+                switch (band.op) {
+                    case Op::Posterize:
+                        for (int c = 0; c < 3; ++c) px[c] &= keep;
+                        break;
+                    case Op::Xor:
+                        for (int c = 0; c < 3; ++c) px[c] ^= band.mask[static_cast<std::size_t>(c)];
+                        break;
+                    case Op::Rotate:
+                        for (int c = 0; c < 3; ++c) {
+                            px[c] = static_cast<std::uint8_t>((px[c] << band.rotate) |
+                                                              (px[c] >> (8 - band.rotate)));
+                        }
+                        break;
+                    case Op::Swap: {
+                        const std::uint8_t in[3] = {px[0], px[1], px[2]};
+                        for (int c = 0; c < 3; ++c) px[c] = in[band.order[static_cast<std::size_t>(c)]];
+                        break;
+                    }
+                    case Op::None:
+                        break;
+                }
+            }
+        }
+    });
+
+    return canvas;
+}
+
+}  // namespace effector

src/effects/bitcrush.hpp

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "core/effect.hpp"
+
+namespace effector {
+
+// Mangles the bytes of its input band by band: posterising, xoring with a
+// random mask, rotating the bits or shuffling the channels.
+// A pure transform: it needs no source images, and leading a chain with
+// sources loaded it starts from a crop of a randomly chosen one.
+class BitCrushEffect : public Effect {
+public:
+    std::string name() const override { return "bitcrush"; }
+    std::string title() const override { return "Bit crush"; }
+    std::string description() const override {
+        return "Mangles the bytes of random bands: posterises them, xors them with a random "
+               "mask, rotates their bits or shuffles their channels.";
+    }
+    const std::vector<ParamSpec>& params() const override;
+    bool needsSources() const override { return false; }
+
+    Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                 const ParamValues& values) const override;
+};
+
+}  // namespace effector

src/effects/channelsplit.cpp

@@ -0,0 +1,97 @@
+#include "effects/channelsplit.hpp"
+
+#include <algorithm>
+#include <array>
+#include <vector>
+
+#include "core/parallel.hpp"
+#include "effects/source_fill.hpp"
+
+namespace effector {
+
+const std::vector<ParamSpec>& ChannelSplitEffect::params() const {
+    static const std::vector<ParamSpec> specs = {
+        ParamSpec::makeInt("split_amount", "Amount", 12, 0, 1024,
+                           "Furthest in pixels a channel may be moved, along either axis."),
+        ParamSpec::makeChoice("split_mode", "Mode", "global", {"global", "per_band"},
+                              "global moves each channel once over the whole image; per_band "
+                              "draws new offsets for every band."),
+        ParamSpec::makeInt("split_band_height", "Band height", 24, 1, 2048,
+                           "Thickness in pixels of each band; per_band mode only."),
+        ParamSpec::makeChoice("split_channels", "Channels", "rgb", {"rgb", "red_cyan", "random"},
+                              "rgb moves all three channels apart; red_cyan moves red one way and "
+                              "green and blue the other, as 3D glasses would; random moves one "
+                              "channel picked at random."),
+    };
+    return specs;
+}
+
+namespace {
+
+struct Offset {
+    int dx = 0;
+    int dy = 0;
+};
+
+using ChannelOffsets = std::array<Offset, 3>;
+
+ChannelOffsets drawOffsets(Rng& rng, int amount, const std::string& channels) {
+    ChannelOffsets offsets{};
+    auto draw = [&] {
+        return Offset{static_cast<int>(rng.inRange(-amount, amount)),
+                      static_cast<int>(rng.inRange(-amount, amount))};
+    };
+    if (channels == "red_cyan") {
+        const Offset red = draw();
+        offsets[0] = red;
+        offsets[1] = offsets[2] = Offset{-red.dx, -red.dy};
+    } else if (channels == "random") {
+        offsets[rng.below(2)] = draw();
+    } else {
+        for (auto& offset : offsets) offset = draw();
+    }
+    return offsets;
+}
+
+}  // namespace
+
+Image ChannelSplitEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                                 const ParamValues& values) const {
+    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
+
+    const int amount = static_cast<int>(std::max(0L, paramInt(values, "split_amount", 12)));
+    const bool perBand = paramChoice(values, "split_mode", "global") == "per_band";
+    const int bandHeight = static_cast<int>(std::max(1L, paramInt(values, "split_band_height", 24)));
+    const std::string channels = paramChoice(values, "split_channels", "rgb");
+
+    const Image input = canvasFromSources(sources, width, height, rng);
+
+    // One set of offsets per band, a single band covering everything in global
+    // mode; all of them drawn before the pixels are touched.
+    const int band = perBand ? bandHeight : height;
+    const int bandCount = (height + band - 1) / band;
+    std::vector<ChannelOffsets> plan;
+    plan.reserve(static_cast<std::size_t>(bandCount));
+    for (int i = 0; i < bandCount; ++i) plan.push_back(drawOffsets(rng, amount, channels));
+
+    Image canvas(width, height);
+    parallelFor(static_cast<std::size_t>(height), [&](std::size_t begin, std::size_t end) {
+        for (std::size_t y = begin; y < end; ++y) {
+            const ChannelOffsets& offsets = plan[y / static_cast<std::size_t>(band)];
+            std::uint8_t* out = canvas.row(static_cast<int>(y));
+            for (int c = 0; c < 3; ++c) {
+                const Offset& offset = offsets[static_cast<std::size_t>(c)];
+                const int sy = std::clamp(static_cast<int>(y) - offset.dy, 0, height - 1);
+                const std::uint8_t* in = input.row(sy);
+                for (int x = 0; x < width; ++x) {
+                    const int sx = std::clamp(x - offset.dx, 0, width - 1);
+                    out[static_cast<std::size_t>(x) * 3 + c] = in[static_cast<std::size_t>(sx) * 3 + c];
+                }
+            }
+        }
+    });
+
+    return canvas;
+}
+
+}  // namespace effector

src/effects/channelsplit.hpp

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "core/effect.hpp"
+
+namespace effector {
+
+// Knocks the red, green and blue planes out of register, either the whole image
+// at once or band by band, each band with offsets of its own.
+// A pure transform: it needs no source images, and leading a chain with
+// sources loaded it starts from a crop of a randomly chosen one.
+class ChannelSplitEffect : public Effect {
+public:
+    std::string name() const override { return "channelsplit"; }
+    std::string title() const override { return "Channel split"; }
+    std::string description() const override {
+        return "Knocks the red, green and blue planes out of register, over the whole image or "
+               "band by band.";
+    }
+    const std::vector<ParamSpec>& params() const override;
+    bool needsSources() const override { return false; }
+
+    Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                 const ParamValues& values) const override;
+};
+
+}  // namespace effector

src/effects/corrupt.cpp

@@ -0,0 +1,143 @@
+#include "effects/corrupt.hpp"
+
+#include <algorithm>
+#include <cstring>
+#include <vector>
+
+#include "core/parallel.hpp"
+#include "effects/sampling.hpp"
+#include "effects/source_fill.hpp"
+
+namespace effector {
+
+const std::vector<ParamSpec>& CorruptEffect::params() const {
+    static const std::vector<ParamSpec> specs = {
+        ParamSpec::makeInt("corrupt_block", "Block size", 16, 2, 256,
+                           "Width and height in pixels of one block, as a codec would cut them."),
+        ParamSpec::makeDouble("corrupt_rate", "Rate", 0.08, 0.0, 1.0,
+                              "Chance of each block being damaged."),
+        ParamSpec::makeChoice("corrupt_kinds", "Damage", "mixed",
+                              {"mixed", "repeat", "displace", "colour"},
+                              "repeat freezes a block into a copy of the one to its left, "
+                              "displace pulls one in from elsewhere in the image, colour knocks "
+                              "it off colour; mixed picks one of them for every block."),
+        ParamSpec::makeBool("corrupt_bleed", "Bleed", false,
+                            "Carry each damaged block's fault on to the end of its row, the way "
+                            "one broken bit spoils the rest of a stream."),
+    };
+    return specs;
+}
+
+namespace {
+
+enum class Damage : std::uint8_t { None, Repeat, Displace, Colour };
+
+struct Block {
+    Damage damage = Damage::None;
+    int sx = 0;  // displace: where the block is read from
+    int sy = 0;
+    int shift[3] = {0, 0, 0};  // colour: added to each channel
+};
+
+}  // namespace
+
+Image CorruptEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                            const ParamValues& values) const {
+    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
+
+    const int size = static_cast<int>(std::max(2L, paramInt(values, "corrupt_block", 16)));
+    const double rate = std::clamp(paramDouble(values, "corrupt_rate", 0.08), 0.0, 1.0);
+    const std::string kinds = paramChoice(values, "corrupt_kinds", "mixed");
+    const bool bleed = paramBool(values, "corrupt_bleed", false);
+
+    const Image input = canvasFromSources(sources, width, height, rng);
+
+    const int cols = (width + size - 1) / size;
+    const int rows = (height + size - 1) / size;
+
+    auto drawBlock = [&](int bx) {
+        Block block;
+        if (kinds == "repeat") block.damage = Damage::Repeat;
+        else if (kinds == "displace") block.damage = Damage::Displace;
+        else if (kinds == "colour") block.damage = Damage::Colour;
+        else block.damage = static_cast<Damage>(1 + rng.below(2));
+        // The first block of a row has nothing to its left to repeat.
+        if (block.damage == Damage::Repeat && bx == 0) block.damage = Damage::Displace;
+        if (block.damage == Damage::Displace) {
+            block.sx = static_cast<int>(rng.inRange(0, std::max(0, width - size)));
+            block.sy = static_cast<int>(rng.inRange(0, std::max(0, height - size)));
+        } else if (block.damage == Damage::Colour) {
+            for (int& shift : block.shift) shift = static_cast<int>(rng.inRange(-128, 128));
+        }
+        return block;
+    };
+
+    // The whole damage map is drawn up front, block by block in reading order.
+    std::vector<Block> plan(static_cast<std::size_t>(cols) * rows);
+    for (int by = 0; by < rows; ++by) {
+        const Block* carried = nullptr;
+        for (int bx = 0; bx < cols; ++bx) {
+            Block& block = plan[static_cast<std::size_t>(by) * cols + bx];
+            if (carried != nullptr) {
+                block = *carried;
+                // A displaced run keeps moving along with the row, so the
+                // stretch reads as one shifted strip rather than one block
+                // over and over.
+                if (block.damage == Damage::Displace) block.sx += size;
+                carried = &block;
+                continue;
+            }
+            if (!chance(rng.next(), rate)) continue;
+            block = drawBlock(bx);
+            if (bleed) carried = &block;
+        }
+    }
+
+    Image canvas = input;
+    // Block rows are independent (a repeat only ever reads to its left), so
+    // they run in parallel and each walks its row in order.
+    parallelFor(static_cast<std::size_t>(rows), [&](std::size_t begin, std::size_t end) {
+        for (std::size_t by = begin; by < end; ++by) {
+            const int y0 = static_cast<int>(by) * size;
+            const int h = std::min(size, height - y0);
+            for (int bx = 0; bx < cols; ++bx) {
+                const Block& block = plan[by * static_cast<std::size_t>(cols) + bx];
+                if (block.damage == Damage::None) continue;
+                const int x0 = bx * size;
+                const int w = std::min(size, width - x0);
+                const std::size_t bytes = static_cast<std::size_t>(w) * 3;
+
+                for (int line = 0; line < h; ++line) {
+                    std::uint8_t* out = canvas.row(y0 + line) + static_cast<std::size_t>(x0) * 3;
+                    switch (block.damage) {
+                        case Damage::Repeat:
+                            std::memmove(out, out - static_cast<std::size_t>(size) * 3, bytes);
+                            break;
+                        case Damage::Displace: {
+                            const int sy = std::min(block.sy + line, height - 1);
+                            const std::uint8_t* in = input.row(sy);
+                            for (int x = 0; x < w; ++x) {
+                                const int sx = (block.sx + x) % width;
+                                std::memcpy(out + static_cast<std::size_t>(x) * 3,
+                                            in + static_cast<std::size_t>(sx) * 3, 3);
+                            }
+                            break;
+                        }
+                        case Damage::Colour:
+                            for (std::size_t i = 0; i < bytes; ++i) {
+                                out[i] = static_cast<std::uint8_t>(
+                                    std::clamp(out[i] + block.shift[i % 3], 0, 255));
+                            }
+                            break;
+                        case Damage::None:
+                            break;
+                    }
+                }
+            }
+        }
+    });
+
+    return canvas;
+}
+
+}  // namespace effector

src/effects/corrupt.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "core/effect.hpp"
+
+namespace effector {
+
+// Imitates a damaged video stream: blocks of the image are frozen into a copy of
+// their neighbour, pulled in from elsewhere or knocked off colour, and with
+// bleeding switched on the damage runs on to the end of the row.
+// A pure transform: it needs no source images, and leading a chain with
+// sources loaded it starts from a crop of a randomly chosen one.
+class CorruptEffect : public Effect {
+public:
+    std::string name() const override { return "corrupt"; }
+    std::string title() const override { return "Corruption"; }
+    std::string description() const override {
+        return "Imitates a damaged video stream: random blocks are smeared, displaced or knocked "
+               "off colour, optionally bleeding on to the end of their row.";
+    }
+    const std::vector<ParamSpec>& params() const override;
+    bool needsSources() const override { return false; }
+
+    Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                 const ParamValues& values) const override;
+};
+
+}  // namespace effector

src/effects/feedback.cpp

@@ -0,0 +1,103 @@
+#include "effects/feedback.hpp"
+
+#include <algorithm>
+#include <cmath>
+#include <vector>
+
+#include "core/parallel.hpp"
+#include "effects/sampling.hpp"
+#include "effects/source_fill.hpp"
+
+namespace effector {
+
+const std::vector<ParamSpec>& FeedbackEffect::params() const {
+    static const std::vector<ParamSpec> specs = {
+        ParamSpec::makeInt("echo_count", "Echoes", 6, 1, 64,
+                           "How many times the image is laid back over itself."),
+        ParamSpec::makeDouble("echo_scale", "Scale", 0.85, 0.1, 2.0,
+                              "Size of each echo against the one before; below 1 the echoes "
+                              "tunnel inwards, above 1 they burst outwards.",
+                              0.01),
+        ParamSpec::makeDouble("echo_rotate", "Rotation", 4.0, -180.0, 180.0,
+                              "Turn in degrees of each echo against the one before.", 0.5, 1),
+        ParamSpec::makeInt("echo_drift", "Drift", 20, 0, 4096,
+                           "Furthest in pixels each echo may wander off centre, either way."),
+        ParamSpec::makeDouble("echo_fade", "Opacity", 0.8, 0.0, 1.0,
+                              "How strongly each echo covers what lies beneath it."),
+    };
+    return specs;
+}
+
+namespace {
+
+struct Echo {
+    double dx = 0.0;
+    double dy = 0.0;
+};
+
+}  // namespace
+
+Image FeedbackEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                             const ParamValues& values) const {
+    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
+
+    const long count = std::clamp(paramInt(values, "echo_count", 6), 1L, 64L);
+    const double scale = std::clamp(paramDouble(values, "echo_scale", 0.85), 0.1, 2.0);
+    const double rotate = std::clamp(paramDouble(values, "echo_rotate", 4.0), -180.0, 180.0);
+    const int drift = static_cast<int>(std::max(0L, paramInt(values, "echo_drift", 20)));
+    const double fade = std::clamp(paramDouble(values, "echo_fade", 0.8), 0.0, 1.0);
+
+    const Image input = canvasFromSources(sources, width, height, rng);
+
+    std::vector<Echo> echoes(static_cast<std::size_t>(count));
+    for (auto& echo : echoes) {
+        echo.dx = static_cast<double>(rng.inRange(-drift, drift));
+        echo.dy = static_cast<double>(rng.inRange(-drift, drift));
+    }
+
+    double sine = 0.0;
+    double cosine = 1.0;
+    sinCosDegrees(rotate, sine, cosine);
+    const double cx = (width - 1) * 0.5;
+    const double cy = (height - 1) * 0.5;
+    const int mix = static_cast<int>(fade * 256.0 + 0.5);
+
+    // A camera filming its own monitor: every pass lays the whole picture so
+    // far, shrunk (or grown), turned and drifted, over the untouched input, so
+    // the older echoes nest inside the newer ones and fade as they go.
+    Image frame = input;
+    Image next(width, height);
+    for (const Echo& echo : echoes) {
+        parallelFor(static_cast<std::size_t>(height), [&](std::size_t begin, std::size_t end) {
+            for (std::size_t row = begin; row < end; ++row) {
+                const std::uint8_t* base = input.row(static_cast<int>(row));
+                std::uint8_t* out = next.row(static_cast<int>(row));
+                const double ry = static_cast<double>(row) - cy - echo.dy;
+                for (int col = 0; col < width; ++col) {
+                    const std::size_t at = static_cast<std::size_t>(col) * 3;
+                    const double rx = col - cx - echo.dx;
+                    const double sx = cx + (rx * cosine + ry * sine) / scale;
+                    const double sy = cy + (-rx * sine + ry * cosine) / scale;
+                    if (sx < 0.0 || sy < 0.0 || sx > width - 1 || sy > height - 1) {
+                        out[at] = base[at];
+                        out[at + 1] = base[at + 1];
+                        out[at + 2] = base[at + 2];
+                        continue;
+                    }
+                    std::uint8_t echoed[3];
+                    sampleBilinear(frame, sx, sy, echoed);
+                    for (int c = 0; c < 3; ++c) {
+                        const int under = base[at + static_cast<std::size_t>(c)];
+                        out[at + static_cast<std::size_t>(c)] =
+                            static_cast<std::uint8_t>(under + (echoed[c] - under) * mix / 256);
+                    }
+                }
+            }
+        });
+        std::swap(frame, next);
+    }
+
+    return frame;
+}
+
+}  // namespace effector

src/effects/feedback.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "core/effect.hpp"
+
+namespace effector {
+
+// Lays the image over itself again and again, each copy zoomed, turned and
+// drifted a little further and fading as it goes, like a camera filming its
+// own monitor.
+// A pure transform: it needs no source images, and leading a chain with
+// sources loaded it starts from a crop of a randomly chosen one.
+class FeedbackEffect : public Effect {
+public:
+    std::string name() const override { return "feedback"; }
+    std::string title() const override { return "Feedback"; }
+    std::string description() const override {
+        return "Lays the image over itself again and again, each copy zoomed, turned and drifted "
+               "further and fading, like a camera filming its own monitor.";
+    }
+    const std::vector<ParamSpec>& params() const override;
+    bool needsSources() const override { return false; }
+
+    Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                 const ParamValues& values) const override;
+};
+
+}  // namespace effector

src/effects/overlay.cpp

@@ -32,6 +32,28 @@ const std::vector<ParamSpec>& OverlayEffect::params() const {
         ParamSpec::makeDouble("overlay_opacity", "Opacity", 1.0, 0.0, 1.0,
                               "How strongly the image is mixed over the input; its own "
                               "transparency is taken into account as well."),
+        ParamSpec::makeChoice("overlay_halo", "Halo", "none", {"none", "shadow", "glow"},
+                              "Draws a soft copy of the image's outline beneath it: a shadow, "
+                              "moved by the shadow offset, or a glow all around it."),
+        ParamSpec::makeColor("overlay_shadow_color", "Shadow colour", "#000000",
+                             "The colour of the shadow."),
+        ParamSpec::makeColor("overlay_glow_color", "Glow colour", "#ffffff",
+                             "The colour of the glow."),
+        ParamSpec::makeInt("overlay_halo_size", "Halo size", 12, 0, 500,
+                           "How far the shadow or glow fades out, in pixels; 0 gives a hard "
+                           "edge."),
+        ParamSpec::makeDouble("overlay_halo_spread", "Halo spread", 0.0, 0.0, 0.9,
+                              "Pushes the full strength of the shadow or glow out from the "
+                              "image's edge before it starts to fade; a glow usually wants some."),
+        ParamSpec::makeDouble("overlay_halo_opacity", "Halo opacity", 0.75, 0.0, 1.0,
+                              "How strongly the shadow or glow is drawn, on top of the image's "
+                              "own opacity."),
+        ParamSpec::makeInt("overlay_shadow_x", "Shadow X", 8, -2000, 2000,
+                           "Moves the shadow right by this many pixels (left when negative); "
+                           "a glow stays centred."),
+        ParamSpec::makeInt("overlay_shadow_y", "Shadow Y", 8, -2000, 2000,
+                           "Moves the shadow down by this many pixels (up when negative); a "
+                           "glow stays centred."),
     };
     return specs;
 }
@@ -123,6 +145,44 @@ void sampleOverlay(const Image& src, const std::uint8_t* alpha, double u, double
     }
 }
 
+// One box blur pass over a line of the halo mask. Unlike the blur effect's the
+// window counts zero beyond both ends, so the halo fades out at the edge of
+// the mask instead of smearing its last value outwards. Integers throughout,
+// so a seed reproduces the halo byte for byte on any machine.
+void maskPass(const std::int32_t* in, std::int32_t* out, int count, std::size_t stride,
+              int radius) {
+    const int window = 2 * radius + 1;
+    std::int32_t sum = 0;
+    for (int i = 0; i <= radius && i < count; ++i) sum += in[static_cast<std::size_t>(i) * stride];
+    for (int i = 0; i < count; ++i) {
+        out[static_cast<std::size_t>(i) * stride] = (sum + window / 2) / window;
+        if (i + radius + 1 < count) sum += in[static_cast<std::size_t>(i + radius + 1) * stride];
+        if (i - radius >= 0) sum -= in[static_cast<std::size_t>(i - radius) * stride];
+    }
+}
+
+// Three box passes each way, which is close enough to a gaussian: `size` is
+// roughly how far the result reaches past the edge of what was covered.
+void blurMask(std::vector<std::int32_t>& mask, int width, int height, int size) {
+    if (size <= 0) return;
+    const int radius = std::max(1, (size + 2) / 3);
+    std::vector<std::int32_t> scratch(mask.size());
+    for (int pass = 0; pass < 3; ++pass) {
+        parallelFor(static_cast<std::size_t>(height), [&](std::size_t begin, std::size_t end) {
+            for (std::size_t y = begin; y < end; ++y) {
+                const std::size_t offset = y * static_cast<std::size_t>(width);
+                maskPass(mask.data() + offset, scratch.data() + offset, width, 1, radius);
+            }
+        });
+        parallelFor(static_cast<std::size_t>(width), [&](std::size_t begin, std::size_t end) {
+            for (std::size_t x = begin; x < end; ++x) {
+                maskPass(scratch.data() + x, mask.data() + x, height,
+                         static_cast<std::size_t>(width), radius);
+            }
+        });
+    }
+}
+
 }  // namespace
 
 void OverlayEffect::loadOverlay(const std::string& path, Image& image,
@@ -187,11 +247,100 @@ Image OverlayEffect::render(const std::vector<Image>& sources, int width, int he
     const int lastRow = tiling ? height : std::min(height, place.y + place.height);
     const int firstCol = tiling ? 0 : std::max(0, place.x);
     const int lastCol = tiling ? width : std::min(width, place.x + place.width);
-    if (firstRow >= lastRow || firstCol >= lastCol) return canvas;  // entirely off the canvas
-
     const int mix = static_cast<int>(opacity * 255.0 + 0.5);
     const std::uint8_t* alphaData = alpha.data();
 
+    // The halo goes down first, so that the image covers it wherever it is
+    // opaque and shows it through wherever it is not.
+    const std::string halo = paramChoice(values, "overlay_halo", "none");
+    const double haloOpacity =
+        std::clamp(paramDouble(values, "overlay_halo_opacity", 0.75), 0.0, 1.0);
+    if ((halo == "shadow" || halo == "glow") && haloOpacity > 0.0) {
+        const bool shadow = halo == "shadow";
+        const int size =
+            static_cast<int>(std::clamp<long>(paramInt(values, "overlay_halo_size", 12), 0, 500));
+        const int reach = 3 * std::max(1, (size + 2) / 3);
+        const int shiftX = shadow ? static_cast<int>(paramInt(values, "overlay_shadow_x", 8)) : 0;
+        const int shiftY = shadow ? static_cast<int>(paramInt(values, "overlay_shadow_y", 8)) : 0;
+        std::uint8_t colour[3];
+        paramColor(values, shadow ? "overlay_shadow_color" : "overlay_glow_color",
+                   shadow ? "#000000" : "#ffffff", colour);
+
+        // The mask covers the canvas as the shadow sees it (moved back by the
+        // offset) plus the blur's reach, so that parts of the image lying off
+        // the canvas still cast onto it. Outside the image nothing is covered,
+        // so the mask is cut down to the image plus that reach as well.
+        int left = -shiftX - reach;
+        int top = -shiftY - reach;
+        int right = width - shiftX + reach;
+        int bottom = height - shiftY + reach;
+        if (!tiling) {
+            left = std::max(left, place.x - reach);
+            top = std::max(top, place.y - reach);
+            right = std::min(right, place.x + place.width + reach);
+            bottom = std::min(bottom, place.y + place.height + reach);
+        }
+        if (left < right && top < bottom) {
+            const int maskWidth = right - left;
+            const int maskHeight = bottom - top;
+            std::vector<std::int32_t> mask(static_cast<std::size_t>(maskWidth) * maskHeight, 0);
+            parallelFor(static_cast<std::size_t>(maskHeight), [&](std::size_t begin,
+                                                                  std::size_t end) {
+                int rgb[3];
+                int pixelAlpha = 255;
+                for (std::size_t i = begin; i < end; ++i) {
+                    const int y = top + static_cast<int>(i);
+                    if (!tiling && (y < place.y || y >= place.y + place.height)) continue;
+                    const double v = (y - place.y + 0.5) * stepY - 0.5;
+                    std::int32_t* out = mask.data() + i * static_cast<std::size_t>(maskWidth);
+                    for (int x = left; x < right; ++x) {
+                        if (!tiling && (x < place.x || x >= place.x + place.width)) continue;
+                        const double u = (x - place.x + 0.5) * stepX - 0.5;
+                        sampleOverlay(overlay, alphaData, u, v, tiling, rgb, pixelAlpha);
+                        out[x - left] = pixelAlpha;
+                    }
+                }
+            });
+            blurMask(mask, maskWidth, maskHeight, size);
+
+            const int haloMix = static_cast<int>(haloOpacity * mix + 0.5);
+            // Spread amplifies the blurred mask, so the part near the edge
+            // saturates and only the outer rim still fades.
+            const double spread =
+                std::clamp(paramDouble(values, "overlay_halo_spread", 0.0), 0.0, 0.9);
+            const std::int32_t gain = static_cast<std::int32_t>(256.0 / (1.0 - spread) + 0.5);
+            const int fromRow = std::max(0, top + shiftY);
+            const int toRow = std::min(height, bottom + shiftY);
+            const int fromCol = std::max(0, left + shiftX);
+            const int toCol = std::min(width, right + shiftX);
+            if (fromRow < toRow && fromCol < toCol) {
+                parallelFor(static_cast<std::size_t>(toRow - fromRow), [&](std::size_t begin,
+                                                                           std::size_t end) {
+                    for (std::size_t i = begin; i < end; ++i) {
+                        const int y = fromRow + static_cast<int>(i);
+                        const std::int32_t* in =
+                            mask.data() + static_cast<std::size_t>(y - shiftY - top) * maskWidth;
+                        std::uint8_t* out = canvas.row(y);
+                        for (int x = fromCol; x < toCol; ++x) {
+                            const int weight =
+                                std::clamp<int>(in[x - shiftX - left] * gain / 256, 0, 255) *
+                                haloMix / 255;
+                            if (weight == 0) continue;
+                            std::uint8_t* px = out + static_cast<std::size_t>(x) * 3;
+                            for (int c = 0; c < 3; ++c) {
+                                px[c] = static_cast<std::uint8_t>(
+                                    px[c] + (colour[c] - px[c]) * weight / 255);
+                            }
+                        }
+                    }
+                });
+            }
+        }
+    }
+
+    // A shadow can reach the canvas from an image lying wholly beside it.
+    if (firstRow >= lastRow || firstCol >= lastCol) return canvas;
+
     parallelFor(static_cast<std::size_t>(lastRow - firstRow), [&](std::size_t begin,
                                                                  std::size_t end) {
         int rgb[3];

src/effects/overlay.hpp

@@ -11,7 +11,8 @@ namespace effector {
 
 // Lays one picture from disk over its input: a logo, a texture, a frame. The
 // overlay is fitted to the canvas in the chosen way, placed from the top left
-// or from the centre, nudged by an offset and mixed in by its opacity. Like the
+// or from the centre, nudged by an offset and mixed in by its opacity, with a
+// soft shadow or glow cut from its own outline beneath it if asked. Like the
 // blur it needs no source images of its own, so it can lead a chain; given
 // sources it fills the canvas from a randomly chosen one first.
 class OverlayEffect : public Effect {
@@ -20,7 +21,8 @@ public:
     std::string title() const override { return "Image overlay"; }
     std::string description() const override {
         return "Lays a single image from disk over its input, fitted to the canvas, centred or "
-               "not, nudged by an offset and mixed in by its opacity.";
+               "not, nudged by an offset and mixed in by its opacity, optionally with a shadow or "
+               "a glow around it.";
     }
     const std::vector<ParamSpec>& params() const override;
     bool needsSources() const override { return false; }

src/effects/pixelsort.cpp

@@ -0,0 +1,151 @@
+#include "effects/pixelsort.hpp"
+
+#include <algorithm>
+#include <array>
+#include <cstring>
+#include <vector>
+
+#include "core/parallel.hpp"
+#include "effects/sampling.hpp"
+#include "effects/source_fill.hpp"
+
+namespace effector {
+
+const std::vector<ParamSpec>& PixelSortEffect::params() const {
+    static const std::vector<ParamSpec> specs = {
+        ParamSpec::makeDouble("sort_low", "Lower threshold", 0.25, 0.0, 1.0,
+                              "Pixels darker than this break a run and stay where they are."),
+        ParamSpec::makeDouble("sort_high", "Upper threshold", 0.8, 0.0, 1.0,
+                              "Pixels brighter than this break a run and stay where they are."),
+        ParamSpec::makeChoice("sort_key", "Sort by", "luma", {"luma", "hue", "saturation"},
+                              "What orders the pixels inside a run."),
+        ParamSpec::makeChoice("sort_direction", "Direction", "horizontal",
+                              {"horizontal", "vertical"}, "Whether rows or columns are sorted."),
+        ParamSpec::makeBool("sort_reverse", "Reverse", false,
+                            "Sort from high to low instead of from low to high."),
+        ParamSpec::makeDouble("sort_line_chance", "Line chance", 1.0, 0.0, 1.0,
+                              "Chance of each row (or column) being sorted at all."),
+        ParamSpec::makeInt("sort_max_run", "Longest run", 0, 0, 8192,
+                           "Each run is cut after a random length up to this many pixels, which "
+                           "frays the edges of the sorted streaks (0 = no limit)."),
+    };
+    return specs;
+}
+
+namespace {
+
+int luma(const std::uint8_t* px) { return (px[0] * 54 + px[1] * 183 + px[2] * 19) >> 8; }
+
+// Hue on a 0..1535 scale (six sectors of 256), in integers.
+int hue(const std::uint8_t* px) {
+    const int r = px[0], g = px[1], b = px[2];
+    const int hi = std::max({r, g, b});
+    const int lo = std::min({r, g, b});
+    const int range = hi - lo;
+    if (range == 0) return 0;
+    if (hi == r) return g >= b ? (g - b) * 255 / range : 1535 - (b - g) * 255 / range;
+    if (hi == g) return 512 + (b - r) * 255 / range;
+    return 1024 + (r - g) * 255 / range;
+}
+
+int saturation(const std::uint8_t* px) {
+    return std::max({px[0], px[1], px[2]}) - std::min({px[0], px[1], px[2]});
+}
+
+// The image with rows and columns swapped, so vertical sorting is horizontal
+// sorting of the transpose.
+Image transposed(const Image& src) {
+    Image out(src.height(), src.width());
+    parallelFor(static_cast<std::size_t>(src.width()), [&](std::size_t begin, std::size_t end) {
+        for (std::size_t x = begin; x < end; ++x) {
+            std::uint8_t* row = out.row(static_cast<int>(x));
+            for (int y = 0; y < src.height(); ++y) {
+                std::memcpy(row + static_cast<std::size_t>(y) * 3, src.row(y) + x * 3, 3);
+            }
+        }
+    });
+    return out;
+}
+
+struct LinePlan {
+    bool sorted = false;
+    std::uint64_t seed = 0;  // for the run lengths, when they are limited
+};
+
+}  // namespace
+
+Image PixelSortEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                              const ParamValues& values) const {
+    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
+
+    const int low = static_cast<int>(std::clamp(paramDouble(values, "sort_low", 0.25), 0.0, 1.0) * 255.0 + 0.5);
+    const int high = static_cast<int>(std::clamp(paramDouble(values, "sort_high", 0.8), 0.0, 1.0) * 255.0 + 0.5);
+    const std::string keyName = paramChoice(values, "sort_key", "luma");
+    const bool vertical = paramChoice(values, "sort_direction", "horizontal") == "vertical";
+    const bool reverse = paramBool(values, "sort_reverse", false);
+    const double lineChance = std::clamp(paramDouble(values, "sort_line_chance", 1.0), 0.0, 1.0);
+    const int maxRun = static_cast<int>(std::max(0L, paramInt(values, "sort_max_run", 0)));
+
+    Image canvas = canvasFromSources(sources, width, height, rng);
+    if (vertical) canvas = transposed(canvas);
+    const int lines = canvas.height();
+    const int span = canvas.width();
+
+    // Which lines are sorted, and a seed for each line's run lengths, are drawn
+    // serially; the lines then sort in parallel, each from its own generator.
+    std::vector<LinePlan> plan(static_cast<std::size_t>(lines));
+    for (auto& line : plan) {
+        line.sorted = chance(rng.next(), lineChance);
+        if (maxRun > 0) line.seed = rng.next();
+    }
+
+    auto keyOf = [&](const std::uint8_t* px) {
+        if (keyName == "hue") return hue(px);
+        if (keyName == "saturation") return saturation(px);
+        return luma(px);
+    };
+
+    parallelFor(static_cast<std::size_t>(lines), [&](std::size_t begin, std::size_t end) {
+        std::vector<std::pair<int, std::array<std::uint8_t, 3>>> run;
+        for (std::size_t line = begin; line < end; ++line) {
+            if (!plan[line].sorted) continue;
+            Rng runRng(plan[line].seed);
+            std::uint8_t* row = canvas.row(static_cast<int>(line));
+
+            auto flush = [&](int start) {
+                // A stable sort, so equal keys keep their order on every
+                // standard library.
+                std::stable_sort(run.begin(), run.end(), [&](const auto& a, const auto& b) {
+                    return reverse ? a.first > b.first : a.first < b.first;
+                });
+                for (std::size_t i = 0; i < run.size(); ++i) {
+                    std::memcpy(row + (static_cast<std::size_t>(start) + i) * 3, run[i].second.data(), 3);
+                }
+                run.clear();
+            };
+
+            int start = 0;
+            int limit = maxRun > 0 ? static_cast<int>(runRng.inRange(1, maxRun)) : span;
+            for (int x = 0; x < span; ++x) {
+                const std::uint8_t* px = row + static_cast<std::size_t>(x) * 3;
+                const int brightness = luma(px);
+                if (brightness < low || brightness > high) {
+                    flush(start);
+                    start = x + 1;
+                    continue;
+                }
+                if (static_cast<int>(run.size()) >= limit) {
+                    flush(start);
+                    start = x;
+                    if (maxRun > 0) limit = static_cast<int>(runRng.inRange(1, maxRun));
+                }
+                run.push_back({keyOf(px), {px[0], px[1], px[2]}});
+            }
+            flush(start);
+        }
+    });
+
+    return vertical ? transposed(canvas) : canvas;
+}
+
+}  // namespace effector

src/effects/pixelsort.hpp

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "core/effect.hpp"
+
+namespace effector {
+
+// Finds runs of pixels whose brightness lies between two thresholds and sorts
+// each run by brightness, hue or saturation, which makes the image drip.
+// A pure transform: it needs no source images, and leading a chain with
+// sources loaded it starts from a crop of a randomly chosen one.
+class PixelSortEffect : public Effect {
+public:
+    std::string name() const override { return "pixelsort"; }
+    std::string title() const override { return "Pixel sort"; }
+    std::string description() const override {
+        return "Sorts the runs of pixels whose brightness lies between two thresholds, along "
+               "rows or columns, so the image melts and drips.";
+    }
+    const std::vector<ParamSpec>& params() const override;
+    bool needsSources() const override { return false; }
+
+    Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                 const ParamValues& values) const override;
+};
+
+}  // namespace effector

src/effects/sampling.hpp

@@ -0,0 +1,69 @@
+#pragma once
+
+#include <algorithm>
+#include <cmath>
+#include <cstdint>
+
+#include "core/image.hpp"
+
+namespace effector {
+
+// Reads the colour at a fractional position, mixing the four neighbouring
+// pixels; positions off the image take the nearest edge pixel. The weights are
+// cut to 1/256 steps so the mix itself is integer arithmetic.
+inline void sampleBilinear(const Image& image, double x, double y, std::uint8_t out[3]) {
+    const int maxX = image.width() - 1;
+    const int maxY = image.height() - 1;
+    x = std::clamp(x, 0.0, static_cast<double>(maxX));
+    y = std::clamp(y, 0.0, static_cast<double>(maxY));
+
+    const int x0 = static_cast<int>(x);
+    const int y0 = static_cast<int>(y);
+    const int x1 = std::min(x0 + 1, maxX);
+    const int y1 = std::min(y0 + 1, maxY);
+    const int fx = static_cast<int>((x - x0) * 256.0);
+    const int fy = static_cast<int>((y - y0) * 256.0);
+
+    const std::uint8_t* a = image.row(y0) + static_cast<std::size_t>(x0) * 3;
+    const std::uint8_t* b = image.row(y0) + static_cast<std::size_t>(x1) * 3;
+    const std::uint8_t* c = image.row(y1) + static_cast<std::size_t>(x0) * 3;
+    const std::uint8_t* d = image.row(y1) + static_cast<std::size_t>(x1) * 3;
+    for (int ch = 0; ch < 3; ++ch) {
+        const int top = a[ch] * (256 - fx) + b[ch] * fx;
+        const int bottom = c[ch] * (256 - fx) + d[ch] * fx;
+        out[ch] = static_cast<std::uint8_t>((top * (256 - fy) + bottom * fy + 32768) >> 16);
+    }
+}
+
+// Sine and cosine of an angle in degrees from nothing but additions and
+// multiplications, so a rotation lands on the same pixels whatever the
+// machine's libm makes of std::sin. The angle is folded into one octant and a
+// short Taylor series does the rest, far below a pixel's worth of error.
+inline void sinCosDegrees(double degrees, double& sine, double& cosine) {
+    const double turns = degrees / 90.0;
+    const double quadrant = std::floor(turns + 0.5);
+    const double x = (turns - quadrant) * 1.5707963267948966;  // [-pi/4, pi/4]
+    const double x2 = x * x;
+    const double s =
+        x * (1.0 - x2 / 6.0 * (1.0 - x2 / 20.0 * (1.0 - x2 / 42.0 * (1.0 - x2 / 72.0))));
+    const double c =
+        1.0 - x2 / 2.0 * (1.0 - x2 / 12.0 * (1.0 - x2 / 30.0 * (1.0 - x2 / 56.0 * (1.0 - x2 / 90.0))));
+    switch (static_cast<int>(quadrant - 4.0 * std::floor(quadrant / 4.0))) {
+        case 0: sine = s; cosine = c; break;
+        case 1: sine = c; cosine = -s; break;
+        case 2: sine = -s; cosine = -c; break;
+        default: sine = -c; cosine = s; break;
+    }
+}
+
+// A uniform double in [0, 1) from the top 53 bits of one rng draw.
+inline double unitDouble(std::uint64_t bits) {
+    return static_cast<double>(bits >> 11) * (1.0 / 9007199254740992.0);
+}
+
+// Whether an event with the given probability happens, from one rng draw.
+inline bool chance(std::uint64_t bits, double probability) {
+    return unitDouble(bits) < probability;
+}
+
+}  // namespace effector

src/effects/shatter.cpp

@@ -0,0 +1,178 @@
+#include "effects/shatter.hpp"
+
+#include <algorithm>
+#include <cmath>
+#include <limits>
+#include <vector>
+
+#include "core/parallel.hpp"
+#include "effects/sampling.hpp"
+#include "effects/source_fill.hpp"
+
+namespace effector {
+
+const std::vector<ParamSpec>& ShatterEffect::params() const {
+    static const std::vector<ParamSpec> specs = {
+        ParamSpec::makeInt("shatter_cells", "Shards", 40, 2, 5000,
+                           "How many shards the image breaks into."),
+        ParamSpec::makeInt("shatter_displace", "Displacement", 40, 0, 4096,
+                           "Furthest in pixels a shard's picture may slide, along either axis."),
+        ParamSpec::makeDouble("shatter_rotate", "Rotation", 8.0, 0.0, 180.0,
+                              "Largest turn in degrees of a shard's picture, either way.", 0.5, 1),
+        ParamSpec::makeDouble("shatter_zoom", "Zoom", 0.05, 0.0, 0.9,
+                              "Largest zoom in or out of a shard's picture, as a fraction.", 0.01),
+        ParamSpec::makeInt("shatter_crack_width", "Crack width", 2, 0, 64,
+                           "Width in pixels of the cracks between the shards (0 = none)."),
+        ParamSpec::makeColor("shatter_crack_colour", "Crack colour", "#101010",
+                             "Colour the cracks are drawn in."),
+    };
+    return specs;
+}
+
+namespace {
+
+struct Shard {
+    double x = 0.0;  // the point the shard grows around
+    double y = 0.0;
+    double dx = 0.0;
+    double dy = 0.0;
+    double sine = 0.0;
+    double cosine = 1.0;
+    double zoom = 1.0;
+};
+
+// The shard points bucketed on a coarse grid, so finding the two nearest to a
+// pixel looks at a few buckets instead of every point.
+class ShardGrid {
+public:
+    ShardGrid(const std::vector<Shard>& shards, int width, int height) : shards_(shards) {
+        cell_ = std::max(1.0, std::sqrt(static_cast<double>(width) * height /
+                                        static_cast<double>(shards.size())));
+        cols_ = static_cast<int>(width / cell_) + 1;
+        rows_ = static_cast<int>(height / cell_) + 1;
+        buckets_.resize(static_cast<std::size_t>(cols_) * rows_);
+        for (std::size_t i = 0; i < shards.size(); ++i) {
+            buckets_[bucketOf(shards[i].x, shards[i].y)].push_back(static_cast<int>(i));
+        }
+    }
+
+    // The nearest and second nearest shard to (x, y).
+    void nearest(double x, double y, int& first, int& second) const {
+        const int bx = std::clamp(static_cast<int>(x / cell_), 0, cols_ - 1);
+        const int by = std::clamp(static_cast<int>(y / cell_), 0, rows_ - 1);
+        double best = std::numeric_limits<double>::max();
+        double next = best;
+        first = second = -1;
+        const int maxRing = std::max(cols_, rows_);
+        for (int ring = 0; ring <= maxRing; ++ring) {
+            // Anything in this ring is at least (ring - 1) cells away, so once
+            // both answers are closer than that the search is over.
+            const double reach = std::max(0, ring - 1) * cell_;
+            if (second >= 0 && next < reach * reach) break;
+            for (int gy = by - ring; gy <= by + ring; ++gy) {
+                if (gy < 0 || gy >= rows_) continue;
+                const bool edgeRow = gy == by - ring || gy == by + ring;
+                for (int gx = bx - ring; gx <= bx + ring; gx += edgeRow ? 1 : 2 * std::max(ring, 1)) {
+                    if (gx < 0 || gx >= cols_) continue;
+                    for (int index : buckets_[static_cast<std::size_t>(gy) * cols_ + gx]) {
+                        const Shard& shard = shards_[static_cast<std::size_t>(index)];
+                        const double d = (shard.x - x) * (shard.x - x) + (shard.y - y) * (shard.y - y);
+                        if (d < best || (d == best && index < first)) {
+                            next = best;
+                            second = first;
+                            best = d;
+                            first = index;
+                        } else if (d < next || (d == next && index < second)) {
+                            next = d;
+                            second = index;
+                        }
+                    }
+                    if (ring == 0) break;
+                }
+            }
+        }
+    }
+
+private:
+    std::size_t bucketOf(double x, double y) const {
+        const int bx = std::clamp(static_cast<int>(x / cell_), 0, cols_ - 1);
+        const int by = std::clamp(static_cast<int>(y / cell_), 0, rows_ - 1);
+        return static_cast<std::size_t>(by) * cols_ + bx;
+    }
+
+    const std::vector<Shard>& shards_;
+    double cell_ = 1.0;
+    int cols_ = 1;
+    int rows_ = 1;
+    std::vector<std::vector<int>> buckets_;
+};
+
+}  // namespace
+
+Image ShatterEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                            const ParamValues& values) const {
+    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
+
+    const long count = std::max(2L, paramInt(values, "shatter_cells", 40));
+    const int displace = static_cast<int>(std::max(0L, paramInt(values, "shatter_displace", 40)));
+    const double rotate = std::clamp(paramDouble(values, "shatter_rotate", 8.0), 0.0, 180.0);
+    const double zoom = std::clamp(paramDouble(values, "shatter_zoom", 0.05), 0.0, 0.9);
+    const double crackWidth = static_cast<double>(std::max(0L, paramInt(values, "shatter_crack_width", 2)));
+    std::uint8_t crack[3];
+    paramColor(values, "shatter_crack_colour", "#101010", crack);
+
+    const Image input = canvasFromSources(sources, width, height, rng);
+
+    std::vector<Shard> shards(static_cast<std::size_t>(count));
+    for (auto& shard : shards) {
+        shard.x = unitDouble(rng.next()) * width;
+        shard.y = unitDouble(rng.next()) * height;
+        shard.dx = static_cast<double>(rng.inRange(-displace, displace));
+        shard.dy = static_cast<double>(rng.inRange(-displace, displace));
+        sinCosDegrees((unitDouble(rng.next()) * 2.0 - 1.0) * rotate, shard.sine, shard.cosine);
+        shard.zoom = 1.0 + (unitDouble(rng.next()) * 2.0 - 1.0) * zoom;
+    }
+    const ShardGrid grid(shards, width, height);
+
+    Image canvas(width, height);
+    parallelFor(static_cast<std::size_t>(height), [&](std::size_t begin, std::size_t end) {
+        for (std::size_t row = begin; row < end; ++row) {
+            std::uint8_t* out = canvas.row(static_cast<int>(row));
+            const double y = static_cast<double>(row) + 0.5;
+            for (int col = 0; col < width; ++col) {
+                std::uint8_t* px = out + static_cast<std::size_t>(col) * 3;
+                const double x = col + 0.5;
+                int first = 0;
+                int second = 0;
+                grid.nearest(x, y, first, second);
+                const Shard& a = shards[static_cast<std::size_t>(first)];
+
+                if (crackWidth > 0.0 && second >= 0) {
+                    // Distance to the edge between the two nearest shards,
+                    // which is the perpendicular bisector of their points.
+                    const Shard& b = shards[static_cast<std::size_t>(second)];
+                    const double da = (x - a.x) * (x - a.x) + (y - a.y) * (y - a.y);
+                    const double db = (x - b.x) * (x - b.x) + (y - b.y) * (y - b.y);
+                    const double gap = std::sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
+                    if (gap > 0.0 && (db - da) / (2.0 * gap) < crackWidth * 0.5) {
+                        px[0] = crack[0];
+                        px[1] = crack[1];
+                        px[2] = crack[2];
+                        continue;
+                    }
+                }
+
+                // Undo the shard's slide, then its turn and zoom about its point.
+                const double rx = x - a.dx - a.x;
+                const double ry = y - a.dy - a.y;
+                const double sx = a.x + (rx * a.cosine + ry * a.sine) / a.zoom;
+                const double sy = a.y + (-rx * a.sine + ry * a.cosine) / a.zoom;
+                sampleBilinear(input, sx - 0.5, sy - 0.5, px);
+            }
+        }
+    });
+
+    return canvas;
+}
+
+}  // namespace effector

src/effects/shatter.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "core/effect.hpp"
+
+namespace effector {
+
+// Breaks its input into random glass shards (the cells around scattered points),
+// each showing the image shifted, turned and zoomed a little on its own, with
+// optional cracks drawn along the edges.
+// A pure transform: it needs no source images, and leading a chain with
+// sources loaded it starts from a crop of a randomly chosen one.
+class ShatterEffect : public Effect {
+public:
+    std::string name() const override { return "shatter"; }
+    std::string title() const override { return "Shatter"; }
+    std::string description() const override {
+        return "Breaks the image into random shards, each shifted, turned and zoomed on its own, "
+               "with optional cracks between them.";
+    }
+    const std::vector<ParamSpec>& params() const override;
+    bool needsSources() const override { return false; }
+
+    Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                 const ParamValues& values) const override;
+};
+
+}  // namespace effector

src/effects/slitshift.cpp

@@ -0,0 +1,99 @@
+#include "effects/slitshift.hpp"
+
+#include <algorithm>
+#include <cstring>
+#include <vector>
+
+#include "core/parallel.hpp"
+#include "effects/source_fill.hpp"
+
+namespace effector {
+
+const std::vector<ParamSpec>& SlitShiftEffect::params() const {
+    static const std::vector<ParamSpec> specs = {
+        ParamSpec::makeInt("shift_bands", "Bands", 24, 1, 4096,
+                           "How many bands are torn out of place."),
+        ParamSpec::makeInt("shift_max", "Largest shift", 120, 0, 8192,
+                           "Furthest in pixels a band may be pushed, either way."),
+        ParamSpec::makeInt("shift_band_height", "Band height", 16, 1, 2048,
+                           "Thickness in pixels of each band."),
+        ParamSpec::makeInt("shift_height_jitter", "Height jitter", 12, 0, 2048,
+                           "Random +/- variation added to the band thickness (0 = uniform)."),
+        ParamSpec::makeChoice("shift_edge", "Edges", "wrap", {"wrap", "smear", "black"},
+                              "What fills the gap a band leaves: wrap brings in what was pushed "
+                              "off the other side, smear stretches the last pixel, black leaves "
+                              "it empty."),
+        ParamSpec::makeChoice("shift_axis", "Axis", "horizontal", {"horizontal", "vertical"},
+                              "horizontal tears bands of rows sideways, vertical tears bands of "
+                              "columns up and down."),
+    };
+    return specs;
+}
+
+namespace {
+
+// Where the pixel at `index` of a line of `count` is read from once the line is
+// pushed by `offset`, or -1 for an empty (black) pixel.
+int shiftedIndex(int index, int offset, int count, char edge) {
+    const int from = index - offset;
+    if (from >= 0 && from < count) return from;
+    if (edge == 'w') return ((from % count) + count) % count;
+    if (edge == 's') return std::clamp(from, 0, count - 1);
+    return -1;
+}
+
+}  // namespace
+
+Image SlitShiftEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                              const ParamValues& values) const {
+    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
+
+    const long bands = std::max(1L, paramInt(values, "shift_bands", 24));
+    const int maxShift = static_cast<int>(std::max(0L, paramInt(values, "shift_max", 120)));
+    const int bandHeight = static_cast<int>(std::max(1L, paramInt(values, "shift_band_height", 16)));
+    const int jitter = static_cast<int>(std::max(0L, paramInt(values, "shift_height_jitter", 12)));
+    const char edge = paramChoice(values, "shift_edge", "wrap").front();
+    const bool vertical = paramChoice(values, "shift_axis", "horizontal") == "vertical";
+
+    const Image input = canvasFromSources(sources, width, height, rng);
+
+    // Every band is drawn up front, and overlapping bands simply add their
+    // pushes, so what the pixels need is one offset per line.
+    const int lines = vertical ? width : height;
+    const int span = vertical ? height : width;
+    std::vector<int> offsets(static_cast<std::size_t>(lines), 0);
+    for (long band = 0; band < bands; ++band) {
+        int thickness = bandHeight;
+        if (jitter > 0) thickness += static_cast<int>(rng.inRange(-jitter, jitter));
+        thickness = std::clamp(thickness, 1, lines);
+        const int start = static_cast<int>(rng.inRange(0, lines - thickness));
+        const int offset = static_cast<int>(rng.inRange(-maxShift, maxShift));
+        for (int line = start; line < start + thickness; ++line) {
+            offsets[static_cast<std::size_t>(line)] += offset;
+        }
+    }
+
+    Image canvas(width, height);
+    parallelFor(static_cast<std::size_t>(lines), [&](std::size_t begin, std::size_t end) {
+        for (std::size_t line = begin; line < end; ++line) {
+            const int offset = offsets[line];
+            for (int i = 0; i < span; ++i) {
+                const int from = shiftedIndex(i, offset, span, edge);
+                const int x = vertical ? static_cast<int>(line) : i;
+                const int y = vertical ? i : static_cast<int>(line);
+                std::uint8_t* out = canvas.row(y) + static_cast<std::size_t>(x) * 3;
+                if (from < 0) {
+                    out[0] = out[1] = out[2] = 0;
+                    continue;
+                }
+                const int fx = vertical ? x : from;
+                const int fy = vertical ? from : y;
+                std::memcpy(out, input.row(fy) + static_cast<std::size_t>(fx) * 3, 3);
+            }
+        }
+    });
+
+    return canvas;
+}
+
+}  // namespace effector

src/effects/slitshift.hpp

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "core/effect.hpp"
+
+namespace effector {
+
+// Tears its input apart: random bands of rows (or columns) are pushed sideways by a
+// random distance each, the way a video signal loses its sync.
+// A pure transform: it needs no source images, and leading a chain with
+// sources loaded it starts from a crop of a randomly chosen one.
+class SlitShiftEffect : public Effect {
+public:
+    std::string name() const override { return "slitshift"; }
+    std::string title() const override { return "Slit shift"; }
+    std::string description() const override {
+        return "Tears random bands of its input sideways, like a video signal losing sync; "
+               "overlapping bands add their shifts up.";
+    }
+    const std::vector<ParamSpec>& params() const override;
+    bool needsSources() const override { return false; }
+
+    Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                 const ParamValues& values) const override;
+};
+
+}  // namespace effector

src/effects/source_fill.hpp

@@ -2,9 +2,11 @@
 
 #include <algorithm>
 #include <cstring>
+#include <vector>
 
 #include "core/image.hpp"
 #include "core/parallel.hpp"
+#include "core/rng.hpp"
 
 namespace effector {
 
@@ -35,4 +37,20 @@ inline void fillFromSource(Image& canvas, const Image& src, int sx, int sy) {
     });
 }
 
+// The canvas a pure transform starts from: a crop of a randomly chosen source,
+// or black when there is none. Inside a chain the only source is the stage
+// before, which has the canvas size, so no random value is drawn at all; only a
+// transform leading a chain with photographs loaded spends any of the rng here.
+inline Image canvasFromSources(const std::vector<Image>& sources, int width, int height, Rng& rng) {
+    Image canvas(width, height);
+    if (!sources.empty()) {
+        const std::size_t index = rng.below(sources.size() - 1);
+        const Image& src = sources[index];
+        const int sx = static_cast<int>(rng.inRange(0, std::max(0, src.width() - width)));
+        const int sy = static_cast<int>(rng.inRange(0, std::max(0, src.height() - height)));
+        fillFromSource(canvas, src, sx, sy);
+    }
+    return canvas;
+}
+
 }  // namespace effector

src/effects/text.cpp

@@ -5,6 +5,7 @@
 #include <algorithm>
 #include <cmath>
 #include <cstdint>
+#include <numbers>
 
 #include "core/parallel.hpp"
 #include "effects/source_fill.hpp"
@@ -17,31 +18,39 @@ const std::vector<ParamSpec>& TextEffect::params() const {
                             "What to write; a line break starts a new line."),
         ParamSpec::makeText("font_family", "Font", "Sans",
                             "Font family, as it is named on this machine: Sans, Serif, Monospace, "
-                            "\"DejaVu Serif\", ..."),
+                            "\"DejaVu Serif\", ...")
+            .styled(),
         ParamSpec::makeChoice("font_weight", "Weight", "normal",
                               {"thin", "light", "normal", "medium", "semibold", "bold", "heavy"},
                               "How bold the glyphs are; a family without the chosen weight is "
-                              "rendered in the nearest one it has."),
-        ParamSpec::makeBool("font_italic", "Italic", false, "Slants the glyphs."),
+                              "rendered in the nearest one it has.")
+            .styled(),
+        ParamSpec::makeBool("font_italic", "Italic", false, "Slants the glyphs.").styled(),
         ParamSpec::makeDouble("font_size", "Size", 96.0, 4.0, 2000.0,
-                              "Height of the glyphs in pixels.", 1.0, 1),
-        ParamSpec::makeColor("text_color", "Colour", "#ffffff", "The colour of the glyphs."),
+                              "Height of the glyphs in pixels.", 1.0, 1)
+            .styled(),
+        ParamSpec::makeColor("text_color", "Colour", "#ffffff", "The colour of the glyphs.").styled(),
         ParamSpec::makeChoice("text_align", "Alignment", "center", {"left", "center", "right"},
-                              "How several lines line up against each other."),
+                              "How several lines line up against each other.")
+            .styled(),
         ParamSpec::makeInt("text_wrap", "Wrap width", 0, 0, 20000,
                            "Breaks the text into lines no wider than this many pixels; 0 writes "
                            "it as given."),
         ParamSpec::makeChoice("text_box", "Box", "none", {"none", "colour", "image"},
                               "What the text sits on: nothing, a filled rectangle, or a picture "
-                              "from disk cropped to the rectangle."),
+                              "from disk cropped to the rectangle.")
+            .styled(),
         ParamSpec::makeColor("box_color", "Box colour", "#000000",
-                            "The colour the box is filled with."),
+                            "The colour the box is filled with.")
+            .styled(),
         ParamSpec::makePath("box_image", "Box picture",
                             "The picture the box is filled with, scaled to cover it."),
         ParamSpec::makeInt("box_padding", "Box padding", 24, 0, 2000,
-                           "How far the box reaches past the text on every side."),
+                           "How far the box reaches past the text on every side.")
+            .styled(),
         ParamSpec::makeDouble("box_opacity", "Box opacity", 1.0, 0.0, 1.0,
-                              "How strongly the box is mixed over the input."),
+                              "How strongly the box is mixed over the input.")
+            .styled(),
         ParamSpec::makeBool("text_center", "Centre", true,
                             "Places the text in the middle of the canvas rather than at its top "
                             "left corner; the offset is counted from there either way."),
@@ -49,8 +58,13 @@ const std::vector<ParamSpec>& TextEffect::params() const {
                            "Moves the text right by this many pixels (left when negative)."),
         ParamSpec::makeInt("text_offset_y", "Offset Y", 0, -20000, 20000,
                            "Moves the text down by this many pixels (up when negative)."),
+        ParamSpec::makeDouble("text_rotation", "Rotation", 0.0, -360.0, 360.0,
+                              "Turns the text and its box about their centre by this many "
+                              "degrees, clockwise (anticlockwise when negative).",
+                              1.0, 1),
         ParamSpec::makeDouble("text_opacity", "Text opacity", 1.0, 0.0, 1.0,
-                              "How strongly the glyphs are mixed over what is behind them."),
+                              "How strongly the glyphs are mixed over what is behind them.")
+            .styled(),
     };
     return specs;
 }
@@ -189,6 +203,22 @@ void TextEffect::loadBoxImage(const std::string& path, Image& image,
     alpha = cachedAlpha_;
 }
 
+std::string TextEffect::label(const ParamValues& values) const {
+    // Several lines read as one: each run of whitespace becomes a single space.
+    std::string words;
+    bool gap = false;
+    for (const char c : paramText(values, "text", "")) {
+        if (c == ' ' || c == '\t' || c == '\n' || c == '\r') {
+            gap = !words.empty();
+            continue;
+        }
+        if (gap) words += ' ';
+        gap = false;
+        words += c;
+    }
+    return words.empty() ? title() : title() + " (" + words + ")";
+}
+
 Image TextEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
                          const ParamValues& values) const {
     if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
@@ -255,6 +285,18 @@ Image TextEffect::render(const std::vector<Image>& sources, int width, int heigh
     const double boxY = (centre ? (height - boxHeight) / 2.0 : 0.0) +
                         static_cast<double>(paramInt(values, "text_offset_y", 0));
 
+    // The turn is about the middle of the box, so it never moves the text away
+    // from where the centring and the offset put it. Cairo's y points down,
+    // which makes a positive angle clockwise on screen.
+    const double rotation = paramDouble(values, "text_rotation", 0.0);
+    if (rotation != 0.0) {
+        const double cx = boxX + boxWidth / 2.0;
+        const double cy = boxY + boxHeight / 2.0;
+        cairo_translate(cr.get, cx, cy);
+        cairo_rotate(cr.get, rotation * std::numbers::pi / 180.0);
+        cairo_translate(cr.get, -cx, -cy);
+    }
+
     if (drawsBox) {
         cairo_save(cr.get);
         cairo_rectangle(cr.get, boxX, boxY, boxWidth, boxHeight);

src/effects/text.hpp

@@ -28,7 +28,10 @@ public:
                "box filled with a colour or with a picture.";
     }
     const std::vector<ParamSpec>& params() const override;
+    std::string styleKind() const override { return "text"; }
     bool needsSources() const override { return false; }
+    // "Text (Hello world)", so stages writing different words tell apart.
+    std::string label(const ParamValues& values) const override;
 
     Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
                  const ParamValues& values) const override;

src/effects/warp.cpp

@@ -0,0 +1,159 @@
+#include "effects/warp.hpp"
+
+#include <algorithm>
+#include <cmath>
+#include <vector>
+
+#include "core/parallel.hpp"
+#include "effects/sampling.hpp"
+#include "effects/source_fill.hpp"
+
+namespace effector {
+
+const std::vector<ParamSpec>& WarpEffect::params() const {
+    static const std::vector<ParamSpec> specs = {
+        ParamSpec::makeInt("warp_strength", "Strength", 40, 0, 4096,
+                           "How far in pixels the field pushes the image at its strongest."),
+        ParamSpec::makeInt("warp_scale", "Scale", 160, 4, 8192,
+                           "Size in pixels of the largest features in the field."),
+        ParamSpec::makeInt("warp_octaves", "Octaves", 3, 1, 6,
+                           "Finer layers of noise laid over the first; more give a turbulent "
+                           "edge to the flow."),
+        ParamSpec::makeChoice("warp_mode", "Mode", "displace", {"displace", "swirl"},
+                              "displace pushes along the field; swirl flows along its contour "
+                              "lines, which curls the image into eddies."),
+    };
+    return specs;
+}
+
+namespace {
+
+// One layer of value noise: random heights on a lattice `spacing` pixels
+// apart, blended smoothly between the lattice points.
+class NoiseLayer {
+public:
+    NoiseLayer(Rng& rng, int width, int height, double spacing)
+        : spacing_(spacing),
+          cols_(static_cast<int>(width / spacing) + 2),
+          rows_(static_cast<int>(height / spacing) + 2),
+          lattice_(static_cast<std::size_t>(cols_) * rows_) {
+        for (auto& value : lattice_) value = unitDouble(rng.next()) * 2.0 - 1.0;
+    }
+
+    // The height at (x, y) in [-1, 1], and its slope per pixel along x and y.
+    void sample(double x, double y, double& value, double& slopeX, double& slopeY) const {
+        const double gx = x / spacing_;
+        const double gy = y / spacing_;
+        const int ix = std::min(static_cast<int>(gx), cols_ - 2);
+        const int iy = std::min(static_cast<int>(gy), rows_ - 2);
+        const double fx = gx - ix;
+        const double fy = gy - iy;
+        const double sx = fx * fx * (3.0 - 2.0 * fx);
+        const double sy = fy * fy * (3.0 - 2.0 * fy);
+
+        const double a = at(ix, iy);
+        const double b = at(ix + 1, iy);
+        const double c = at(ix, iy + 1);
+        const double d = at(ix + 1, iy + 1);
+        const double cross = a - b - c + d;
+        value = a + (b - a) * sx + (c - a) * sy + cross * sx * sy;
+        slopeX = 6.0 * fx * (1.0 - fx) * ((b - a) + cross * sy) / spacing_;
+        slopeY = 6.0 * fy * (1.0 - fy) * ((c - a) + cross * sx) / spacing_;
+    }
+
+private:
+    double at(int x, int y) const { return lattice_[static_cast<std::size_t>(y) * cols_ + x]; }
+
+    double spacing_;
+    int cols_;
+    int rows_;
+    std::vector<double> lattice_;
+};
+
+// Octaves of noise summed, each twice as fine and half as strong as the one
+// before, and scaled back so the total stays in [-1, 1].
+class NoiseField {
+public:
+    NoiseField(Rng& rng, int width, int height, double scale, int octaves) {
+        double spacing = scale;
+        double weight = 1.0;
+        for (int i = 0; i < octaves; ++i) {
+            layers_.emplace_back(rng, width, height, std::max(1.0, spacing));
+            weights_.push_back(weight);
+            total_ += weight;
+            spacing *= 0.5;
+            weight *= 0.5;
+        }
+    }
+
+    void sample(double x, double y, double& value, double& slopeX, double& slopeY) const {
+        value = slopeX = slopeY = 0.0;
+        for (std::size_t i = 0; i < layers_.size(); ++i) {
+            double v = 0.0, sx = 0.0, sy = 0.0;
+            layers_[i].sample(x, y, v, sx, sy);
+            value += v * weights_[i];
+            slopeX += sx * weights_[i];
+            slopeY += sy * weights_[i];
+        }
+        value /= total_;
+        slopeX /= total_;
+        slopeY /= total_;
+    }
+
+private:
+    std::vector<NoiseLayer> layers_;
+    std::vector<double> weights_;
+    double total_ = 0.0;
+};
+
+}  // namespace
+
+Image WarpEffect::render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                         const ParamValues& values) const {
+    if (width < 1 || height < 1) throw EffectError("Canvas size must be at least 1x1 pixels.");
+
+    const double strength = static_cast<double>(std::max(0L, paramInt(values, "warp_strength", 40)));
+    const double scale = static_cast<double>(std::max(4L, paramInt(values, "warp_scale", 160)));
+    const int octaves = static_cast<int>(std::clamp(paramInt(values, "warp_octaves", 3), 1L, 6L));
+    const bool swirl = paramChoice(values, "warp_mode", "displace") == "swirl";
+
+    const Image input = canvasFromSources(sources, width, height, rng);
+
+    // Lattices are drawn in full before any pixel moves: one field for the
+    // swirl, which flows along its contours, two for a push along x and y.
+    const NoiseField first(rng, width, height, scale, octaves);
+    std::vector<NoiseField> extra;
+    if (!swirl) extra.emplace_back(rng, width, height, scale, octaves);
+
+    Image canvas(width, height);
+    parallelFor(static_cast<std::size_t>(height), [&](std::size_t begin, std::size_t end) {
+        for (std::size_t row = begin; row < end; ++row) {
+            std::uint8_t* out = canvas.row(static_cast<int>(row));
+            const double y = static_cast<double>(row);
+            for (int col = 0; col < width; ++col) {
+                const double x = col;
+                double value = 0.0, slopeX = 0.0, slopeY = 0.0;
+                first.sample(x, y, value, slopeX, slopeY);
+                double dx = 0.0;
+                double dy = 0.0;
+                if (swirl) {
+                    // Along the contour: the slope turned a quarter, which
+                    // never piles pixels up or tears them apart. The slope of
+                    // a field `scale` wide is about 1/scale, hence the factor.
+                    dx = slopeY * scale * strength * 0.5;
+                    dy = -slopeX * scale * strength * 0.5;
+                } else {
+                    double other = 0.0;
+                    extra.front().sample(x, y, other, slopeX, slopeY);
+                    dx = value * strength;
+                    dy = other * strength;
+                }
+                sampleBilinear(input, x + dx, y + dy, out + static_cast<std::size_t>(col) * 3);
+            }
+        }
+    });
+
+    return canvas;
+}
+
+}  // namespace effector

src/effects/warp.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "core/effect.hpp"
+
+namespace effector {
+
+// Pushes every pixel along a smooth random noise field: a haze at low strength,
+// melted paint at high. The swirl mode follows the field's contour lines,
+// which turns the image into eddies instead of ripples.
+// A pure transform: it needs no source images, and leading a chain with
+// sources loaded it starts from a crop of a randomly chosen one.
+class WarpEffect : public Effect {
+public:
+    std::string name() const override { return "warp"; }
+    std::string title() const override { return "Warp"; }
+    std::string description() const override {
+        return "Pushes every pixel along a smooth random noise field, from a gentle haze to "
+               "molten eddies.";
+    }
+    const std::vector<ParamSpec>& params() const override;
+    bool needsSources() const override { return false; }
+
+    Image render(const std::vector<Image>& sources, int width, int height, Rng& rng,
+                 const ParamValues& values) const override;
+};
+
+}  // namespace effector

src/gui/window.hpp

@@ -7,6 +7,7 @@
 #include <memory>
 #include <mutex>
 #include <optional>
+#include <functional>
 #include <string>
 #include <thread>
 #include <vector>
@@ -16,6 +17,7 @@
 #include "core/effect.hpp"
 #include "core/image.hpp"
 #include "core/project.hpp"
+#include "core/style.hpp"
 
 namespace effector {
 
@@ -27,10 +29,34 @@ public:
 private:
     void buildUi();
     Gtk::Widget& buildSidebar();
+    Gtk::Widget& buildChainTab();
+    Gtk::Widget& buildSetupTab();
     Gtk::Widget& buildPreview();
     void buildParamWidgets();
     ParamValues paramValues() const;
-    void storeParams();     // widgets -> the selected stage's values
+    void storeParams();     // widgets -> the selected stage, and its style
+
+    // The style row above the params of a stage whose effect takes one.
+    std::unique_ptr<Gtk::Widget> buildStyleRow(const ChainStage& stage);
+    // The names of the pool the selected stage draws from, in the order the
+    // dropdown shows them.
+    std::vector<std::string> styleNames(const std::string& kind) const;
+    // The style the selected stage follows, or nullptr when it stands alone.
+    Style* selectedStyle();
+    const Style* selectedStyle() const;
+    void onStyleSelected();   // the dropdown: adopt, drop, or make a new one
+    void adoptStyle(const std::string& name);
+    void onNewStyle();
+    void onRenameStyle();
+    void onRemoveStyle();
+    // The little modal that asks for a style name, used by both New and
+    // Rename. Built from scratch each time, like the progress window.
+    void askStyleName(const std::string& title, const std::string& initial,
+                      const std::function<void(const std::string&)>& accept);
+    void closeStyleWindow();
+    // A name that is empty, or already used in the pool, is refused in place.
+    bool styleNameTaken(const std::string& kind, const std::string& name) const;
+
     void applyInitial(const Options& initial);
 
     bool canRender() const;     // a chain, and sources if the chain needs them
@@ -48,7 +74,9 @@ private:
     void closeLoadWindow();
     void cancelLoad();
     void appendSourceRow(const std::string& path);
-    void updateSourcesLabel();  // the collapsed expander shows the count
+    void updateSourcesLabel();  // the heading shows the count
+    // The whole sources section only shows while the chain asks for sources.
+    void updateSourcesVisible();
 
     Gtk::Widget& buildCanvasSection();
     // "" while "Custom" is picked, otherwise the format's key.
@@ -63,16 +91,35 @@ private:
     Gtk::Widget& buildAddMenu();      // the menu of effects that can be appended
     void appendStage(const EffectPtr& effect);
     void removeStage(int index);
-    void moveStage(int index, int delta);
+    void moveStage(int from, int to);  // `to` is the index it ends up at
+    // Dragging a row: the slot between rows it would drop into, and the line
+    // that shows it.
+    int chainDropSlot(double y) const;
+    void showChainDropSlot(int slot);
+    // The check on a chain row: the stage stays where it is, and is skipped.
+    void setStageEnabled(int index, bool enabled);
     void rebuildChainRows();
+    // Rests the split under the chain's rows, until the user drags it.
+    void scheduleChainSplitFit();
+    void fitChainSplit();
+    void refitChainSplit();  // the double-click on the handle
+    void onChainSplitMoved();
+    std::string stageLabel(std::size_t index) const;
     void selectStage(int index);
     void onStageSelected();
     Gtk::Widget& buildMainMenu();     // the header menu: new, open, save project
+    void showChangelog();
+    void showAbout();
     Project currentProject() const;
     void applyProject(const Project& project, const std::string& path);
     void clearSources();
     void onNewProject();
     void onOpenProject();
+    void openProject(const std::string& path);
+    // Open Recent: the projects this program opened or saved, newest first,
+    // kept in the desktop's shared list of recently used files.
+    void rememberProject(const std::string& path);
+    void rebuildRecentMenu();
     void onProjectChosen(const Glib::RefPtr<Gio::AsyncResult>& result,
                          const Glib::RefPtr<Gtk::FileDialog>& dialog);
     void onSaveProject();       // falls back to Save As while the project is untitled
@@ -110,11 +157,25 @@ private:
     // The cascade: stage 0 works on the sources, every later stage on the
     // output of the one before it.
     std::vector<ChainStage> stages_;
+    // The named looks the stages share. Edited through the params of whichever
+    // stage follows one, and saved with the project.
+    StyleSet styles_;
     int selectedStage_ = 0;
     bool suspendStageSelect_ = false;  // guards the rebuild of the chain rows
+    // The split between the chain and the params, and where it was last put
+    // to fit the rows: any other position the user reached by dragging.
+    Gtk::Paned* chainSplit_ = nullptr;
+    int fittedChainSplit_ = -1;
+    bool chainSplitDragged_ = false;
+    bool suspendSplitTrack_ = false;
+    sigc::connection chainSplitFit_;
+    // The name label of each chain row, renamed in place as params change.
+    std::vector<Gtk::Label*> stageLabels_;
     Image result_;
     std::uint64_t seed_ = 0;
     std::string projectPath_;  // empty until the project has been saved once
+    Glib::RefPtr<Gio::Menu> recentMenu_;
+    sigc::connection recentChanged_;  // the recent list outlives the window
     bool suspendRender_ = true;
 
     // Source loading. Decoding a batch of large photographs takes seconds, so
@@ -150,9 +211,13 @@ private:
     Gtk::Button* addButton_ = nullptr;
     // Built fresh with the progress window, and null whenever it is closed.
     std::unique_ptr<Gtk::Window> loadWindow_;
+    // Opened from the menu on first use, then shown again rather than rebuilt.
+    std::unique_ptr<Gtk::Window> changelogWindow_;
+    std::unique_ptr<Gtk::AboutDialog> aboutDialog_;
     Gtk::ProgressBar* loadBar_ = nullptr;
     Gtk::Label* loadFileLabel_ = nullptr;
-    Gtk::Expander sourcesExpander_;
+    Gtk::Box sourcesSection_;  // hidden while the chain needs no sources
+    Gtk::Label sourcesHeading_;
     Gtk::ListBox sourceList_;
     Gtk::DropDown formatDrop_;
     Gtk::SpinButton widthSpin_;
@@ -162,6 +227,11 @@ private:
     // Set while a format fills the spins, so their own handler does not queue
     // a second render on top of the one the format change asks for.
     bool suspendCanvasSync_ = false;
+    Gtk::DropDown* styleDrop_ = nullptr;   // null while the stage takes no style
+    bool suspendStyleSelect_ = false;      // guards filling the dropdown
+    std::shared_ptr<Gtk::Window> styleWindow_;
+    Gtk::Entry* styleNameEntry_ = nullptr;  // nulled with the window
+    Gtk::Label* styleNameError_ = nullptr;
     Gtk::Grid paramGrid_;
     Gtk::Label paramHeading_;
     Gtk::Entry seedEntry_;

src/main.cpp

@@ -13,12 +13,20 @@
 #include "core/image.hpp"
 #include "core/registry.hpp"
 #include "core/rng.hpp"
+#include "core/version.hpp"
 #include "gui/app.hpp"
 
 namespace {
 
 int renderHeadless(const effector::Options& options) {
-    const auto stages = effector::buildChain(options);
+    auto stages = effector::buildChain(options);
+    // A headless run always renders something, so with no -e the default
+    // effect stands in. The interface has no such need: it opens on an empty
+    // chain and waits for the user to add the first stage.
+    if (stages.empty()) {
+        const auto effect = effector::effectByName(effector::defaultEffectName());
+        stages.push_back({effect, effect->defaults()});
+    }
 
     std::vector<effector::LoadFailure> failures;
 
@@ -71,6 +79,10 @@ int main(int argc, char** argv) {
             std::cout << effector::usage(argv[0]);
             return 0;
         }
+        if (options.showVersion) {
+            std::cout << "effector " << effector::kVersion << "\n";
+            return 0;
+        }
         if (options.listEffects) {
             for (const auto& effect : effector::effects()) {
                 std::cout << effect->name() << "\t" << effect->title() << " - "

tests/CMakeLists.txt

@@ -5,3 +5,19 @@ target_link_libraries(effector_tests PRIVATE effector_core)
 target_compile_options(effector_tests PRIVATE -Wall -Wextra -Wpedantic)
 
 add_test(NAME core COMMAND effector_tests)
+
+# The interface drives the real window, so it needs a display. Under ctest it
+# gets a private Xvfb one when xvfb-run is installed; without it, or without a
+# display of its own, the test reports itself skipped rather than failed.
+add_executable(effector_gui_tests gui_tests.cpp)
+target_link_libraries(effector_gui_tests PRIVATE effector_gui)
+target_compile_options(effector_gui_tests PRIVATE -Wall -Wextra -Wpedantic)
+
+find_program(XVFB_RUN xvfb-run)
+if(XVFB_RUN)
+    add_test(NAME gui COMMAND ${XVFB_RUN} -a -s "-screen 0 1400x900x24"
+             env -u WAYLAND_DISPLAY GDK_BACKEND=x11 $<TARGET_FILE:effector_gui_tests>)
+else()
+    add_test(NAME gui COMMAND effector_gui_tests)
+endif()
+set_tests_properties(gui PROPERTIES SKIP_RETURN_CODE 77)

tests/core_tests.cpp

@@ -1,5 +1,6 @@
 // Small self-contained checks for the pieces that have no GUI dependency.
 
+#include <algorithm>
 #include <array>
 #include <atomic>
 #include <clocale>
@@ -11,6 +12,7 @@
 #include <locale>
 #include <mutex>
 #include <optional>
+#include <set>
 #include <string>
 #include <utility>
 #include <vector>
@@ -21,6 +23,8 @@
 #include "core/project.hpp"
 #include "core/registry.hpp"
 #include "core/rng.hpp"
+#include "core/style.hpp"
+#include "core/version.hpp"
 #include "effects/blur.hpp"
 #include "effects/grain.hpp"
 #include "effects/monochrome.hpp"
@@ -199,6 +203,18 @@ effector::Image flat(int width, int height, std::uint8_t shade) {
     return image;
 }
 
+// Renders any registered effect by name with its defaults, overridden by
+// `values`, from a generator seeded with `seed`.
+effector::Image renderNamed(const std::string& name, const std::vector<effector::Image>& sources,
+                            int width, int height, std::uint64_t seed,
+                            const effector::ParamValues& values) {
+    const auto effect = effector::effectByName(name);
+    effector::Rng rng(seed);
+    auto merged = effect->defaults();
+    for (const auto& [key, value] : values) merged[key] = value;
+    return effect->render(sources, width, height, rng, merged);
+}
+
 effector::Image render(const std::vector<effector::Image>& sources, int width, int height,
                        std::uint64_t seed, const effector::ParamValues& values) {
     effector::ScanlinesEffect effect;
@@ -241,6 +257,15 @@ int main() {
             threw = true;
         }
         check(threw, "unknown effect throws");
+
+        // Flags share one namespace, so a key two effects declared would be
+        // handed to whichever came first.
+        std::set<std::string> keys;
+        bool unique = true;
+        for (const auto& effect : effects()) {
+            for (const auto& spec : effect->params()) unique = keys.insert(spec.key).second && unique;
+        }
+        check(unique, "no two effects declare the same param key");
     }
 
     std::cout << "scanlines\n";
@@ -614,6 +639,49 @@ int main() {
                         solid(100, 100, 0, 0, 255)),
               "zero opacity leaves the input untouched");
 
+        // Halo: none by default, a shadow moved by its offset, a glow all round.
+        check(sameBytes(renderOverlay(blue, 100, 100, at),
+                        renderOverlay(blue, 100, 100, [&] {
+                            ParamValues none = at;
+                            none["overlay_halo"] = std::string("none");
+                            return none;
+                        }())),
+              "no halo is the default");
+        ParamValues shadowed = at;
+        shadowed["overlay_halo"] = std::string("shadow");
+        shadowed["overlay_halo_size"] = 0L;
+        shadowed["overlay_halo_opacity"] = 1.0;
+        shadowed["overlay_shadow_x"] = 5L;
+        shadowed["overlay_shadow_y"] = 5L;
+        const auto shadow = renderOverlay(blue, 100, 100, shadowed);
+        const auto dark = pixel(shadow, 72, 62);  // past the logo's bottom right corner (70, 60)
+        check(dark[0] == 0 && dark[1] == 0 && dark[2] == 0,
+              "a hard shadow is cast down and right by its offset");
+        check(isBlue(pixel(shadow, 28, 50)) && isRed(pixel(shadow, 50, 50)),
+              "it leaves the other side alone and stays beneath the image");
+        shadowed["overlay_halo_size"] = 12L;
+        const auto soft = pixel(renderOverlay(blue, 100, 100, shadowed), 78, 50);
+        check(soft[2] > 0 && soft[2] < 255, "a soft shadow fades out past the edge");
+
+        ParamValues glowing = at;
+        glowing["overlay_halo"] = std::string("glow");
+        const auto glow = renderOverlay(blue, 100, 100, glowing);
+        const auto left = pixel(glow, 27, 50);
+        const auto right = pixel(glow, 72, 50);
+        check(left[0] > 0 && left[0] == right[0] && left[1] == right[1],
+              "a glow lightens both sides alike");
+        check(isBlue(pixel(glow, 2, 2)), "and fades out before the far corners");
+        glowing["overlay_halo_spread"] = 0.5;
+        check(pixel(renderOverlay(blue, 100, 100, glowing), 27, 50)[0] > left[0],
+              "spread strengthens the halo near the edge");
+
+        ParamValues offCanvas = shadowed;
+        offCanvas["overlay_halo_size"] = 0L;
+        offCanvas["overlay_offset_x"] = -70L;  // the logo ends just left of the canvas
+        offCanvas["overlay_shadow_x"] = 20L;
+        const auto cast = pixel(renderOverlay(blue, 100, 100, offCanvas), 5, 50);
+        check(cast[2] == 0, "an image off the canvas still casts its shadow onto it");
+
         // No image chosen is the state the interface starts in: a pass through.
         check(sameBytes(renderOverlay(blue, 100, 100, {}), solid(100, 100, 0, 0, 255)),
               "with no image chosen the stage passes its input through");
@@ -735,6 +803,20 @@ int main() {
         check(countRed(moved, 100, 60, 200, 120) > 0 && countRed(moved, 0, 0, 100, 60) == 0,
               "the offset moves it down and to the right");
 
+        // A wide line turned a quarter stands upright: it reaches above and
+        // below the band it filled unturned, and no longer out to the sides.
+        ParamValues wide = plain;
+        wide["text"] = std::string("HHHHHH");
+        wide["font_size"] = 40.0;
+        const auto flat = renderText(blue, 200, 120, wide);
+        ParamValues turned = wide;
+        turned["text_rotation"] = 90.0;
+        const auto upright = renderText(blue, 200, 120, turned);
+        check(countRed(flat, 0, 0, 200, 25) == 0 && countRed(upright, 0, 0, 200, 25) > 0,
+              "rotation turns the text about its centre");
+        check(countRed(flat, 0, 0, 50, 120) > 0 && countRed(upright, 0, 0, 50, 120) == 0,
+              "and takes it in from the sides");
+
         // Weight and size are the two knobs the glyphs themselves answer to: a
         // bolder or a larger setting covers strictly more of the canvas.
         ParamValues bold = plain;
@@ -819,6 +901,13 @@ int main() {
         // Like blur and overlay it needs no sources of its own, and the same
         // settings render the same bytes twice over.
         check(!TextEffect().needsSources(), "text can lead a chain");
+
+        // A text stage is named after its words, on one line.
+        check(TextEffect().label({{"text", std::string("  Two\nlines ")}}) == "Text (Two lines)",
+              "a text stage is labelled with its words");
+        check(TextEffect().label({{"text", std::string(" \n")}}) == "Text",
+              "a text stage with no words is labelled with the title alone");
+        check(effectByName("blur")->label({}) == "Blur", "other effects are labelled with their title");
         const auto alone = renderText({}, 200, 120, plain);
         check(alone.width() == 200 && countRed(alone, 0, 0, 200, 120) > 0,
               "without sources it draws on an empty canvas");
@@ -828,6 +917,254 @@ int main() {
         std::filesystem::remove_all(dir);
     }
 
+    std::cout << "text styles\n";
+    {
+        const std::vector<Image> blue = {solid(200, 120, 0, 0, 255)};
+        const auto countRed = [](const Image& image) {
+            int found = 0;
+            for (int y = 0; y < image.height(); ++y) {
+                for (int x = 0; x < image.width(); ++x) {
+                    if (isRed(pixel(image, x, y))) ++found;
+                }
+            }
+            return found;
+        };
+
+        const auto specs = styleSpecs("text");
+        const auto carries = [&specs](const std::string& key) {
+            return std::any_of(specs.begin(), specs.end(),
+                               [&key](const ParamSpec& spec) { return spec.key == key; });
+        };
+        check(specs.size() == 11, "a text style carries eleven params");
+        check(carries("font_family") && carries("font_weight") && carries("font_italic") &&
+                  carries("font_size") && carries("text_color") && carries("text_align") &&
+                  carries("text_opacity") && carries("text_box") && carries("box_color") &&
+                  carries("box_padding") && carries("box_opacity"),
+              "the look is what it carries");
+        check(!carries("text") && !carries("text_wrap") && !carries("box_image") &&
+                  !carries("text_center") && !carries("text_offset_x") && !carries("text_offset_y") &&
+                  !carries("text_rotation"),
+              "the words and the placement stay on the stage");
+        check(styleSpecs("").empty() && styleSpecs("nosuchkind").empty(),
+              "a kind no effect claims carries nothing");
+        check(paramDouble(styleDefaults("text"), "font_size", 0.0) == 96.0 &&
+                  styleDefaults("text").size() == specs.size(),
+              "a fresh style starts at the defaults the effect declares");
+
+        StyleSet styles = {{"text", "Title", styleDefaults("text")}};
+        styles[0].values["font_size"] = 40.0;
+        styles[0].values["text_color"] = std::string("#ff0000");
+        check(findStyle(styles, "text", "Title") != nullptr &&
+                  findStyle(styles, "text", "Caption") == nullptr &&
+                  findStyle(styles, "other", "Title") == nullptr,
+              "a style is found by its kind and its name");
+
+        const ChainStage own{effectByName("text"),
+                             {{"text", std::string("Hi")},
+                              {"font_size", 12.0},
+                              {"text_color", std::string("#ff0000")}},
+                             true,
+                             ""};
+        ChainStage follows = own;
+        follows.style = "Title";
+
+        check(paramDouble(stageValues(own, styles), "font_size", 0.0) == 12.0,
+              "a stage on its own keeps the settings it was given");
+        check(paramDouble(stageValues(follows, styles), "font_size", 0.0) == 40.0,
+              "a stage following a style takes the style's");
+        check(paramText(stageValues(follows, styles), "text", "") == "Hi",
+              "and keeps its own words either way");
+
+        Rng ownRng(3);
+        Rng followRng(3);
+        const auto small = renderChain({own}, blue, 200, 120, ownRng, styles);
+        const auto large = renderChain({follows}, blue, 200, 120, followRng, styles);
+        check(countRed(small) > 0 && countRed(large) > countRed(small),
+              "the style is what actually reaches the render");
+
+        // The whole point: two stages, one style, one look in two places.
+        ChainStage left = follows;
+        left.values["text_offset_x"] = -40L;
+        ChainStage right = follows;
+        right.values["text_offset_x"] = 40L;
+        Rng leftRng(3);
+        Rng rightRng(3);
+        const auto leftImage = renderChain({left}, blue, 200, 120, leftRng, styles);
+        const auto rightImage = renderChain({right}, blue, 200, 120, rightRng, styles);
+        check(countRed(leftImage) == countRed(large) && countRed(rightImage) == countRed(large),
+              "two stages following one style ink the same glyphs");
+        check(!sameBytes(leftImage, rightImage), "each in its own place");
+
+        StyleSet edited = styles;
+        edited[0].values["font_size"] = 20.0;
+        Rng editedLeft(3);
+        Rng editedRight(3);
+        const auto afterLeft = renderChain({left}, blue, 200, 120, editedLeft, edited);
+        const auto afterRight = renderChain({right}, blue, 200, 120, editedRight, edited);
+        check(countRed(afterLeft) < countRed(leftImage) &&
+                  countRed(afterRight) < countRed(rightImage) &&
+                  countRed(afterLeft) == countRed(afterRight),
+              "editing the style moves every stage that follows it");
+
+        ChainStage missing = follows;
+        missing.style = "Nowhere";
+        Rng missingRng(3);
+        Rng bareRng(3);
+        check(sameBytes(renderChain({missing}, blue, 200, 120, missingRng, styles),
+                        renderChain({own}, blue, 200, 120, bareRng)),
+              "naming a style that is not there renders as standing alone");
+
+        Rng noStyleRng(3);
+        Rng noPoolRng(3);
+        check(sameBytes(renderChain({follows}, blue, 200, 120, noStyleRng, {}),
+                        renderChain({own}, blue, 200, 120, noPoolRng)),
+              "and so does a chain handed no styles at all");
+    }
+
+    std::cout << "chaos transforms\n";
+    {
+        const std::vector<Image> sources = {gradient(1200, 800, 10), gradient(640, 480, 90)};
+        const std::vector<Image> input = {gradient(400, 300, 40)};
+
+        // What every one of them must do, and what switches each one off.
+        const std::vector<std::pair<std::string, ParamValues>> transforms = {
+            {"slitshift", {{"shift_max", 0L}}},
+            {"channelsplit", {{"split_amount", 0L}}},
+            {"pixelsort", {{"sort_line_chance", 0.0}}},
+            {"corrupt", {{"corrupt_rate", 0.0}}},
+            {"shatter",
+             {{"shatter_displace", 0L}, {"shatter_rotate", 0.0}, {"shatter_zoom", 0.0},
+              {"shatter_crack_width", 0L}}},
+            {"warp", {{"warp_strength", 0L}}},
+            {"bitcrush", {{"crush_coverage", 0.0}}},
+            {"feedback", {{"echo_fade", 0.0}}},
+        };
+        for (const auto& [name, off] : transforms) {
+            check(!effectByName(name)->needsSources(), name + " needs no source images");
+
+            const auto first = renderNamed(name, sources, 400, 300, 4, {});
+            const auto again = renderNamed(name, sources, 400, 300, 4, {});
+            const auto other = renderNamed(name, sources, 400, 300, 11, {});
+            check(first.width() == 400 && first.height() == 300,
+                  name + " renders the requested size");
+            check(sameBytes(first, again), name + " reproduces itself from a seed");
+            check(!sameBytes(first, other), name + " changes with the seed");
+            check(!sameBytes(renderNamed(name, input, 400, 300, 4, {}), input[0]),
+                  name + " changes its input");
+            check(sameBytes(renderNamed(name, input, 400, 300, 4, off), input[0]),
+                  name + " switched right down leaves its input alone");
+
+            const auto blank = renderNamed(name, {}, 120, 80, 1, {});
+            check(blank.width() == 120 && blank.height() == 80,
+                  name + " renders without sources");
+
+            ChainStage scanlines{effectByName("scanlines"), {{"strip_height", 6L}}};
+            ChainStage stage{effectByName(name), {}};
+            Rng a(9);
+            Rng b(9);
+            check(sameBytes(renderChain({scanlines, stage}, sources, 300, 200, a),
+                            renderChain({scanlines, stage}, sources, 300, 200, b)),
+                  name + " cascades reproducibly");
+            check(!chainNeedsSources({stage, scanlines}), "a chain led by " + name + " needs no sources");
+
+            // A canvas one pixel wide or high must not trip any of them up.
+            check(renderNamed(name, {}, 1, 1, 2, {}).width() == 1 &&
+                      renderNamed(name, input, 1, 57, 2, {}).height() == 57 &&
+                      renderNamed(name, input, 57, 1, 2, {}).width() == 57,
+                  name + " copes with a sliver of a canvas");
+        }
+
+        // Wrapped slit shifts only rotate each row, so every row keeps its
+        // pixels, just not their places.
+        const auto wrapped = renderNamed("slitshift", input, 400, 300, 5, {{"shift_bands", 200L}});
+        bool rotated = true;
+        for (int y = 0; y < 300; ++y) {
+            std::vector<std::uint8_t> before(input[0].row(y), input[0].row(y) + 1200);
+            std::vector<std::uint8_t> after(wrapped.row(y), wrapped.row(y) + 1200);
+            std::sort(before.begin(), before.end());
+            std::sort(after.begin(), after.end());
+            rotated = rotated && before == after;
+        }
+        check(rotated, "a wrapped slit shift keeps every row's pixels");
+        const auto upright = renderNamed("slitshift", input, 400, 300, 5,
+                                         {{"shift_axis", std::string("vertical")}});
+        check(!sameBytes(upright, wrapped), "the vertical axis tears columns instead");
+
+        // Moving a plane of one colour moves nothing that can be seen.
+        const auto split = renderNamed("channelsplit", {solid(80, 60, 200, 90, 30)}, 80, 60, 3,
+                                       {{"split_mode", std::string("per_band")},
+                                        {"split_band_height", 7L}});
+        check(sameBytes(split, solid(80, 60, 200, 90, 30)), "a channel split keeps a flat colour");
+        const auto rc = renderNamed("channelsplit", input, 400, 300, 3,
+                                    {{"split_channels", std::string("red_cyan")}});
+        check(pixel(rc, 200, 150)[2] == pixel(input[0], 200, 150)[2],
+              "red_cyan leaves blue where a flat plane has it");
+
+        // With the thresholds wide open every row comes out sorted.
+        const auto sorted = renderNamed("pixelsort", {stripes(64, 16)}, 64, 16, 1,
+                                        {{"sort_low", 0.0}, {"sort_high", 1.0}});
+        bool ordered = true;
+        for (int y = 0; y < 16; ++y) {
+            for (int x = 1; x < 64; ++x) ordered = ordered && pixel(sorted, x - 1, y)[0] <= pixel(sorted, x, y)[0];
+        }
+        check(ordered, "an open pixel sort orders every row");
+        const auto downward = renderNamed("pixelsort", {stripes(64, 16)}, 64, 16, 1,
+                                          {{"sort_low", 0.0}, {"sort_high", 1.0},
+                                           {"sort_direction", std::string("vertical")}});
+        check(sameBytes(downward, stripes(64, 16)), "sorting uniform columns changes nothing");
+
+        // Every block repeated is the first block smeared across the row.
+        const auto smeared = renderNamed("corrupt", input, 64, 32, 2,
+                                         {{"corrupt_rate", 1.0},
+                                          {"corrupt_block", 16L},
+                                          {"corrupt_kinds", std::string("repeat")}});
+        bool periodic = true;
+        for (int y = 0; y < 32; ++y) {
+            for (int x = 16; x < 64; ++x) periodic = periodic && pixel(smeared, x, y) == pixel(smeared, x - 16, y);
+        }
+        check(periodic, "repeated blocks copy the block to their left");
+        const auto bled = renderNamed("corrupt", input, 400, 300, 2,
+                                      {{"corrupt_rate", 0.02}, {"corrupt_bleed", true}});
+        check(!sameBytes(bled, renderNamed("corrupt", input, 400, 300, 2, {{"corrupt_rate", 0.02}})),
+              "bleeding carries the damage further");
+
+        const auto cracked = renderNamed("shatter", {flat(200, 150, 128)}, 200, 150, 6,
+                                         {{"shatter_crack_colour", std::string("#ff0000")}});
+        bool red = false;
+        for (int y = 0; y < 150; ++y) {
+            for (int x = 0; x < 200; ++x) red = red || isRed(pixel(cracked, x, y));
+        }
+        check(red, "shatter draws its cracks in the crack colour");
+
+        check(!sameBytes(renderNamed("warp", input, 400, 300, 4, {{"warp_mode", std::string("swirl")}}),
+                         renderNamed("warp", input, 400, 300, 4, {})),
+              "swirl flows differently from a plain push");
+
+        const auto poster = renderNamed("bitcrush", input, 400, 300, 3,
+                                        {{"crush_op", std::string("posterize")},
+                                         {"crush_coverage", 1.0}});
+        bool coarse = true;
+        for (std::size_t i = 0; i < poster.byteSize(); ++i) coarse = coarse && poster.data()[i] % 8 == 0;
+        check(coarse, "posterising three bits leaves multiples of eight");
+        const auto swapped = renderNamed("bitcrush", {solid(40, 40, 250, 120, 5)}, 40, 40, 3,
+                                         {{"crush_op", std::string("channel_swap")},
+                                          {"crush_coverage", 1.0}});
+        check(pixel(swapped, 20, 20) != std::array<int, 3>{250, 120, 5},
+              "a channel swap never leaves the order as it was");
+
+        // A shrunk, fully opaque echo lands the image's corner inside the
+        // canvas, while the border outside every echo stays the input's.
+        const auto tunnel = renderNamed("feedback", input, 400, 300, 1,
+                                        {{"echo_scale", 0.5}, {"echo_rotate", 0.0},
+                                         {"echo_drift", 0L}, {"echo_fade", 1.0}});
+        check(pixel(tunnel, 0, 0) == pixel(input[0], 0, 0), "the border outside the echoes is the input");
+        // Halfway to the corner reads the corner of the image at half size.
+        const auto near = pixel(tunnel, 100, 75);
+        check(std::abs(near[0] - pixel(input[0], 0, 0)[0]) < 4 &&
+                  std::abs(near[1] - pixel(input[0], 0, 0)[1]) < 4,
+              "the echoes nest inside it");
+    }
+
     std::cout << "chain\n";
     {
         std::vector<Image> sources = {gradient(1200, 800, 10), gradient(640, 480, 90)};
@@ -889,6 +1226,50 @@ int main() {
             scanlinesThrew = true;
         }
         check(scanlinesThrew, "scanlines still refuses to run without sources");
+
+        // A stage switched off is skipped whole: it is handed no image and
+        // draws nothing from the shared rng, so the cascade comes out exactly
+        // as it would have without that stage in it at all.
+        ChainStage blurOff = blur;
+        blurOff.enabled = false;
+        ChainStage scanlinesOff = scanlines;
+        scanlinesOff.enabled = false;
+
+        Rng skipping(5);
+        const auto skipped = renderChain({scanlines, blurOff}, sources, 400, 300, skipping);
+        check(sameBytes(skipped, direct), "a disabled stage is skipped, its rng draws with it");
+        check(chainTitle({scanlines, blurOff}) == "Scanlines", "the title names only what ran");
+        check(chainSlug({scanlines, blurOff}) == "scanlines", "and so does the slug");
+
+        // Whoever leads the chain is handed the sources, and that is the first
+        // stage still switched on.
+        check(!chainNeedsSources({scanlinesOff, blur}),
+              "a disabled leading stage leaves the question to the stage behind it");
+        Rng leading(5);
+        const auto ledByBlur = renderChain({scanlinesOff, blur}, {}, 200, 150, leading);
+        check(sameBytes(ledByBlur, sourceless), "the stage behind it leads instead");
+
+        bool allOffThrew = false;
+        try {
+            Rng rng(1);
+            renderChain({scanlinesOff, blurOff}, sources, 100, 100, rng);
+        } catch (const EffectError&) {
+            allOffThrew = true;
+        }
+        check(allOffThrew, "a chain with every stage disabled throws");
+
+        // The command line switches a stage off by effect name, the same way
+        // the params pick out the stage they belong to.
+        const auto cli =
+            parsedOptions({"-e", "scanlines", "-e", "blur", "--disable", "blur", "--radius", "4"});
+        check(cli.has_value(), "--disable is accepted");
+        const auto cliStages = buildChain(*cli);
+        check(cliStages.size() == 2 && cliStages[0].enabled && !cliStages[1].enabled,
+              "--disable keeps the stage in the chain and switches it off");
+        check(paramInt(cliStages[1].values, "radius", 0) == 4,
+              "a switched-off stage still takes its flags");
+        check(!parsedOptions({"-e", "blur", "--disable", "nope"}).has_value(),
+              "--disable refuses an unknown effect");
     }
 
     std::cout << "project\n";
@@ -949,6 +1330,86 @@ int main() {
         check(stripped.stages[0].values.find("radius") == stripped.stages[0].values.end(),
               "a stage only keeps the params its effect declares");
 
+        // A stage switched off keeps its place and its settings in the file and
+        // comes back switched off; nothing is written for the ordinary case.
+        Project toggled = project;
+        toggled.stages[1].enabled = false;
+        const auto offFile = dir / "disabled.json";
+        saveProject(offFile.string(), toggled);
+        const auto offBack = loadProject(offFile.string());
+        check(offBack.stages.size() == 2 && offBack.stages[0].enabled && !offBack.stages[1].enabled,
+              "a switched-off stage comes back switched off");
+        check(paramInt(offBack.stages[1].values, "radius", 0) == 3,
+              "and with the settings it was switched off with");
+        check(projectToJson(toggled).find("\"enabled\"") != std::string::npos &&
+                  projectToJson(project).find("\"enabled\"") == std::string::npos,
+              "only a switched-off stage is written out as one");
+
+        // Styles ride along with the chain, and the stages come back pointing
+        // at the ones they followed.
+        Project stylish;
+        stylish.styles = {{"text", "Title", styleDefaults("text")},
+                          {"text", "Caption", styleDefaults("text")}};
+        stylish.styles[0].values["font_size"] = 120.0;
+        stylish.styles[0].values["text_color"] = std::string("#ff8800");
+        stylish.styles[1].values["font_family"] = std::string("Serif");
+        stylish.stages.push_back(
+            {effectByName("text"), {{"text", std::string("One")}}, true, "Title"});
+        stylish.stages.push_back(
+            {effectByName("text"), {{"text", std::string("Two")}}, true, "Title"});
+        stylish.stages.push_back(
+            {effectByName("text"), {{"text", std::string("Three")}}, true, ""});
+
+        const auto styleFile = dir / "styles.json";
+        saveProject(styleFile.string(), stylish);
+        const auto styleBack = loadProject(styleFile.string());
+        check(styleBack.styles.size() == 2 && styleBack.styles[0].name == "Title" &&
+                  styleBack.styles[1].name == "Caption" && styleBack.styles[0].kind == "text",
+              "the styles survive a round trip");
+        check(paramDouble(styleBack.styles[0].values, "font_size", 0.0) == 120.0 &&
+                  paramText(styleBack.styles[0].values, "text_color", "") == "#ff8800" &&
+                  paramText(styleBack.styles[1].values, "font_family", "") == "Serif",
+              "and so do the values they carry");
+        check(styleBack.stages[0].style == "Title" && styleBack.stages[1].style == "Title" &&
+                  styleBack.stages[2].style.empty(),
+              "and which stage follows which");
+        check(paramDouble(stageValues(styleBack.stages[0], styleBack.styles), "font_size", 0.0) ==
+                      120.0 &&
+                  paramDouble(stageValues(styleBack.stages[2], styleBack.styles), "font_size",
+                              0.0) == 96.0,
+              "a reloaded project resolves its styles as it did");
+        check(projectToJson(stylish).find("\"styles\"") != std::string::npos &&
+                  projectToJson(project).find("\"styles\"") == std::string::npos &&
+                  projectToJson(project).find("\"style\"") == std::string::npos,
+              "a project with no styles writes nothing about them");
+
+        // Everything that can be wrong with a style is dropped on its own,
+        // leaving a project that still opens and still renders.
+        const auto lenient = projectFromJson(R"({
+          "styles": [
+            {"kind": "nosuchkind", "name": "Ghost", "params": {}},
+            {"kind": "text", "name": "", "params": {}},
+            {"kind": "text", "name": "Title", "params": {"font_size": 60, "nonsense": 3}},
+            {"kind": "text", "name": "Title", "params": {"font_size": 12}}
+          ],
+          "chain": [
+            {"effect": "text", "style": "Title", "params": {"text": "Kept"}},
+            {"effect": "text", "style": "Gone", "params": {"font_size": 30}},
+            {"effect": "blur", "style": "Title", "params": {}}
+          ]
+        })");
+        check(lenient.styles.size() == 1 && lenient.styles[0].name == "Title",
+              "an unknown kind, a nameless style and a repeated name are dropped");
+        check(paramDouble(lenient.styles[0].values, "font_size", 0.0) == 60.0 &&
+                  lenient.styles[0].values.find("nonsense") == lenient.styles[0].values.end(),
+              "a style only keeps the params its kind declares, and the first of a name wins");
+        check(lenient.stages[0].style == "Title" && lenient.stages[1].style.empty(),
+              "a stage naming a style that is not there is cut loose");
+        check(lenient.stages[2].style.empty(),
+              "and so is one whose effect takes no style at all");
+        check(paramDouble(stageValues(lenient.stages[1], lenient.styles), "font_size", 0.0) == 30.0,
+              "which leaves it rendering the values written beside it");
+
         int refusals = 0;
         for (const char* bad : {"{\"chain\": [{\"effect\": \"nope\"}]}", "{\"chain\": []}",
                                 "{\"chain\": [{\"effect\": \"blur\"},]}", "not json at all"}) {
@@ -1255,6 +1716,21 @@ int main() {
         std::filesystem::remove_all(dir);
     }
 
+    std::cout << "version\n";
+    {
+        // A release is the version in CMakeLists.txt and its entry at the top
+        // of CHANGELOG.md; bumping one without the other fails here.
+        const std::string_view log = kChangelog;
+        const auto newest = log.find("\n## [");
+        check(newest != std::string_view::npos &&
+                  log.substr(newest + 5).starts_with(std::string(kVersion) + "]"),
+              "the newest changelog entry is this version");
+        const auto options = parsedOptions({"--version"});
+        check(options && options->showVersion, "--version is understood");
+        const auto shortOptions = parsedOptions({"-V"});
+        check(shortOptions && shortOptions->showVersion, "and so is -V");
+    }
+
     std::cout << (failures == 0 ? "\nall checks passed\n" : "\n" + std::to_string(failures) + " failed\n");
     return failures == 0 ? 0 : 1;
 }

tests/gui_tests.cpp

@@ -0,0 +1,477 @@
+// Checks for the interface, driven through the real window: the widgets are
+// found by what a user sees (a name, a tooltip, a label) and pressed the way a
+// click would press them. Needs a display; exits 77 (skipped) without one.
+
+#include <gtkmm.h>
+
+#include <chrono>
+#include <cstdlib>
+#include <filesystem>
+#include <iostream>
+#include <memory>
+#include <string>
+#include <thread>
+#include <vector>
+
+#include "cli/options.hpp"
+#include "core/project.hpp"
+#include "core/registry.hpp"
+#include "core/version.hpp"
+#include "gui/window.hpp"
+
+namespace {
+
+int failures = 0;
+
+void check(bool condition, const std::string& what) {
+    if (condition) {
+        std::cout << "  ok   " << what << "\n";
+    } else {
+        std::cout << "  FAIL " << what << "\n";
+        ++failures;
+    }
+}
+
+// Lets the main loop run for a while: popovers map, renders come back, and
+// the rows rebuilt by a click are laid out.
+void pump(int milliseconds = 100) {
+    auto context = Glib::MainContext::get_default();
+    const auto until = std::chrono::steady_clock::now() + std::chrono::milliseconds(milliseconds);
+    while (std::chrono::steady_clock::now() < until) {
+        while (context->pending()) context->iteration(false);
+        std::this_thread::sleep_for(std::chrono::milliseconds(5));
+    }
+}
+
+template <typename T, typename Pred>
+void collect(Gtk::Widget& root, Pred pred, std::vector<T*>& out) {
+    for (auto* child = root.get_first_child(); child != nullptr; child = child->get_next_sibling()) {
+        if (auto* match = dynamic_cast<T*>(child); match != nullptr && pred(*match)) out.push_back(match);
+        collect<T>(*child, pred, out);
+    }
+}
+
+template <typename T>
+std::vector<T*> all(Gtk::Widget& root) {
+    std::vector<T*> out;
+    collect<T>(root, [](T&) { return true; }, out);
+    return out;
+}
+
+template <typename T>
+T* named(Gtk::Widget& root, const std::string& name) {
+    std::vector<T*> out;
+    collect<T>(root, [&](T& w) { return w.get_name() == name; }, out);
+    return out.empty() ? nullptr : out.front();
+}
+
+Gtk::Button* withTooltip(Gtk::Widget& root, const std::string& tip) {
+    std::vector<Gtk::Button*> out;
+    collect<Gtk::Button>(root, [&](Gtk::Button& b) { return b.get_tooltip_text() == tip; }, out);
+    return out.empty() ? nullptr : out.front();
+}
+
+bool isAncestor(const Gtk::Widget& ancestor, const Gtk::Widget& widget) {
+    for (auto* w = widget.get_parent(); w != nullptr; w = w->get_parent()) {
+        if (w == &ancestor) return true;
+    }
+    return false;
+}
+
+int rowCount(Gtk::ListBox& list) {
+    int count = 0;
+    while (list.get_row_at_index(count) != nullptr) ++count;
+    return count;
+}
+
+std::string rowTitle(Gtk::ListBox& list, int index) {
+    auto* row = list.get_row_at_index(index);
+    if (row == nullptr) return {};
+    const auto labels = all<Gtk::Label>(*row);
+    return labels.empty() ? std::string{} : std::string(labels.front()->get_text());
+}
+
+// The top of `widget` in the window's coordinates.
+double topIn(Gtk::Widget& widget, Gtk::Widget& window) {
+    graphene_rect_t bounds;
+    if (!gtk_widget_compute_bounds(widget.gobj(), window.gobj(), &bounds)) return -1.0;
+    return bounds.origin.y;
+}
+
+// The menu of effects: the popover the "Add effect" button opens, and the
+// entry in it for one effect.
+Gtk::Button* menuEntry(Gtk::Popover& menu, const std::string& title) {
+    for (auto* button : all<Gtk::Button>(menu)) {
+        if (button->get_label() == title) return button;
+    }
+    return nullptr;
+}
+
+// Presses a button the way the keyboard does. GTK shows the press for a
+// quarter of a second before the button reports the click, so wait it out.
+void press(Gtk::Button& button) {
+    button.activate();
+    pump(400);
+}
+
+bool addFromMenu(Gtk::MenuButton& add, const std::string& title) {
+    auto* menu = add.get_popover();
+    if (menu == nullptr) return false;
+    add.popup();
+    pump();
+    auto* entry = menuEntry(*menu, title);
+    if (entry == nullptr || !menu->get_mapped()) return false;
+    press(*entry);
+    return true;
+}
+
+// The drop target the chain list reorders its rows with.
+GtkDropTarget* chainDropTarget(Gtk::Widget& list) {
+    GListModel* controllers = gtk_widget_observe_controllers(list.gobj());
+    GtkDropTarget* found = nullptr;
+    for (guint i = 0; i < g_list_model_get_n_items(controllers) && found == nullptr; ++i) {
+        auto* controller = g_list_model_get_item(controllers, i);
+        if (GTK_IS_DROP_TARGET(controller)) found = GTK_DROP_TARGET(controller);
+        g_object_unref(controller);
+    }
+    g_object_unref(controllers);
+    return found;
+}
+
+// What dropping the row of stage `index` at `y` does; a real drag needs a
+// pointer, which the tests do not have.
+void dropStage(GtkDropTarget* drop, int index, double y) {
+    GValue value = G_VALUE_INIT;
+    g_value_init(&value, G_TYPE_INT);
+    g_value_set_int(&value, index);
+    gboolean handled = FALSE;
+    g_signal_emit_by_name(drop, "drop", &value, 1.0, y, &handled);
+    g_value_unset(&value);
+}
+
+void runTests(Gtk::Window& window) {
+    const auto& effects = effector::effects();
+
+    std::cout << "sidebar\n";
+    auto* stack = all<Gtk::Stack>(window).empty() ? nullptr : all<Gtk::Stack>(window).front();
+    check(stack != nullptr && stack->get_child_by_name("chain") != nullptr &&
+              stack->get_child_by_name("setup") != nullptr,
+          "the sidebar has a Chain and a Setup tab");
+    check(stack != nullptr && stack->get_visible_child_name() == "chain",
+          "it opens on the Chain tab");
+
+    auto* chainList = named<Gtk::ListBox>(window, "chain-list");
+    auto* add = named<Gtk::MenuButton>(window, "add-effect");
+    auto* sources = named<Gtk::Box>(window, "sources");
+    check(chainList != nullptr && add != nullptr && sources != nullptr,
+          "the chain list, the Add effect button and the sources are there");
+    if (chainList == nullptr || add == nullptr || sources == nullptr) return;
+
+    std::vector<Gtk::Paned*> panes;
+    collect<Gtk::Paned>(window, [&](Gtk::Paned& p) { return isAncestor(p, *chainList); }, panes);
+    auto* split = panes.empty() ? nullptr : panes.back();
+    check(split != nullptr && split->get_orientation() == Gtk::Orientation::VERTICAL,
+          "the Chain tab is a vertical split");
+    check(split != nullptr && split->get_start_child() != nullptr &&
+              isAncestor(*split->get_start_child(), *chainList),
+          "the chain list is above the split");
+    check(split != nullptr && split->get_end_child() != nullptr &&
+              !isAncestor(*split->get_end_child(), *chainList),
+          "the params are below it, apart from the list");
+    check(split != nullptr && !split->get_shrink_start_child() && !split->get_shrink_end_child(),
+          "neither side can be dragged below its minimum");
+    check(topIn(*add, window) >= 0.0 && topIn(*add, window) < topIn(*chainList, window),
+          "Add effect sits above the chain list, not under it");
+    check(isAncestor(*stack->get_child_by_name("setup"), *sources),
+          "the sources are on the Setup tab");
+
+    std::cout << "add effect\n";
+    auto* menu = add->get_popover();
+    check(menu != nullptr, "Add effect has a menu");
+    if (menu == nullptr) return;
+    bool listed = true;
+    for (const auto& effect : effects) listed = listed && menuEntry(*menu, effect->title()) != nullptr;
+    check(listed, "the menu has an entry for every registered effect");
+    check(all<Gtk::Button>(*menu).size() == effects.size(), "and nothing else");
+
+    add->popup();
+    pump();
+    check(menu->get_mapped(), "the menu opens");
+    // A popover taller than the room below its button is not shown at all --
+    // though GTK still calls it mapped -- which is what broke the button once
+    // there were enough effects: the entries have to scroll instead, in a
+    // menu short enough to open below a button near the top of a 768-pixel
+    // screen.
+    const auto scrollers = all<Gtk::ScrolledWindow>(*menu);
+    const int cap = scrollers.empty() ? -1 : scrollers.front()->get_max_content_height();
+    check(!scrollers.empty() && isAncestor(*scrollers.front(), *menuEntry(*menu, effects.front()->title())),
+          "the entries scroll");
+    check(cap > 0 && cap <= 480, "past a height that fits a small screen");
+    check(menu->get_height() > 0 && menu->get_height() <= cap + 40,
+          "and the menu stays within it however many effects there are");
+    add->popdown();
+    pump();
+
+
+    std::vector<Gtk::ScrolledWindow*> listScrollers;
+    collect<Gtk::ScrolledWindow>(window, [&](Gtk::ScrolledWindow& s) {
+        return s.get_child() != nullptr && isAncestor(*s.get_child(), *chainList);
+    }, listScrollers);
+    auto* listScroller = listScrollers.empty() ? nullptr : listScrollers.back();
+    check(listScroller != nullptr && listScroller->get_propagate_natural_height() &&
+              listScroller->get_max_content_height() > 0,
+          "the chain list asks for the height of its rows, up to a cap");
+    const int emptySplit = split != nullptr ? split->get_position() : -1;
+
+    check(rowCount(*chainList) == 0, "the chain starts empty");
+    check(addFromMenu(*add, "Blur"), "picking Blur from the menu");
+    check(!menu->get_mapped(), "closes the menu");
+    check(rowCount(*chainList) == 1 && rowTitle(*chainList, 0) == "1. Blur",
+          "and appends a Blur stage");
+    check(chainList->get_selected_row() == chainList->get_row_at_index(0),
+          "the new stage is selected");
+    check(!sources->get_visible(), "a chain led by blur hides the sources");
+
+    check(addFromMenu(*add, "Scanlines"), "picking Scanlines");
+    check(rowCount(*chainList) == 2 && rowTitle(*chainList, 1) == "2. Scanlines",
+          "appends it after Blur");
+    check(chainList->get_selected_row() == chainList->get_row_at_index(1),
+          "and selects it");
+
+    std::cout << "stage rows\n";
+    if (rowCount(*chainList) != 2) return;
+    auto* second = chainList->get_row_at_index(1);
+    check(second->has_css_class("stage-row"), "a row is a stage row");
+    std::vector<Gtk::Button*> actions;
+    collect<Gtk::Button>(*second, [](Gtk::Button& b) { return b.has_css_class("stage-action"); }, actions);
+    check(actions.size() == 3, "with a move up, a move down and a remove action");
+    auto* first = chainList->get_row_at_index(0);
+    auto* firstUp = withTooltip(*first, "Move up");
+    auto* lastDown = withTooltip(*second, "Move down");
+    check(firstUp != nullptr && !firstUp->get_sensitive(), "the first stage cannot move up");
+    check(lastDown != nullptr && !lastDown->get_sensitive(), "the last stage cannot move down");
+
+    auto* up = withTooltip(*second, "Move up");
+    check(up != nullptr, "the second stage has Move up");
+    if (up != nullptr) press(*up);
+    check(rowTitle(*chainList, 0) == "1. Scanlines" && rowTitle(*chainList, 1) == "2. Blur",
+          "Move up swaps the stages");
+    check(chainList->get_selected_row() == chainList->get_row_at_index(0),
+          "and the moved stage stays selected");
+    check(sources->get_visible(), "a chain led by scanlines shows the sources");
+
+    auto* remove = withTooltip(*chainList->get_row_at_index(0), "Remove");
+    if (remove != nullptr) press(*remove);
+    check(rowCount(*chainList) == 1 && rowTitle(*chainList, 0) == "1. Blur",
+          "Remove drops the stage and renumbers the rest");
+    check(!sources->get_visible(), "and the sources hide again");
+
+    std::cout << "drag and drop\n";
+    addFromMenu(*add, "Scanlines");
+    for (const auto& effect : effects) {
+        if (effect->title() != "Blur" && effect->title() != "Scanlines") {
+            addFromMenu(*add, effect->title());
+            break;
+        }
+    }
+    GtkDropTarget* drop = chainDropTarget(*chainList);
+    check(drop != nullptr, "the chain list takes drops");
+    if (drop != nullptr && rowCount(*chainList) == 3) {
+        const std::string first = rowTitle(*chainList, 0).substr(3);
+        const std::string second = rowTitle(*chainList, 1).substr(3);
+        const std::string third = rowTitle(*chainList, 2).substr(3);
+        const double bottom = chainList->get_row_at_index(2)->get_height() * 3.0;
+        GdkDragAction action = GDK_ACTION_NONE;
+        g_signal_emit_by_name(drop, "motion", 1.0, bottom, &action);
+        check(chainList->get_row_at_index(2)->has_css_class("drop-after"),
+              "dragging past the last row marks its bottom edge");
+        dropStage(drop, 0, bottom);
+        pump();
+        check(rowTitle(*chainList, 0) == "1. " + second && rowTitle(*chainList, 1) == "2. " + third &&
+                  rowTitle(*chainList, 2) == "3. " + first,
+              "dropping the first stage past the last moves it to the end");
+        check(chainList->get_selected_row() == chainList->get_row_at_index(2),
+              "and selects it");
+        check(!chainList->get_row_at_index(2)->has_css_class("drop-after"),
+              "and clears the mark");
+        dropStage(drop, 2, 1.0);
+        pump();
+        check(rowTitle(*chainList, 0) == "1. " + first && rowTitle(*chainList, 1) == "2. " + second,
+              "dropping on the top edge of the first row moves it to the front");
+    }
+    for (int i = rowCount(*chainList) - 1; i > 0; --i) {
+        if (auto* removeRow = withTooltip(*chainList->get_row_at_index(i), "Remove")) press(*removeRow);
+    }
+
+    std::cout << "many stages\n";
+    for (int i = 0; i < 4; ++i) addFromMenu(*add, effects[static_cast<std::size_t>(i) % effects.size()]->title());
+    pump();
+    const int fewSplit = split != nullptr ? split->get_position() : -1;
+    check(split != nullptr && fewSplit > emptySplit,
+          "the split moves down as the chain grows");
+    for (int i = 4; i < 12; ++i) addFromMenu(*add, effects[static_cast<std::size_t>(i) % effects.size()]->title());
+    check(rowCount(*chainList) == 13, "the menu still works with a long chain");
+    check(addFromMenu(*add, effects.back()->title()) && rowCount(*chainList) == 14,
+          "including for the last effect in the menu");
+    pump();
+    const int longSplit = split != nullptr ? split->get_position() : -1;
+    check(longSplit > fewSplit && listScroller != nullptr &&
+              listScroller->get_height() <= listScroller->get_max_content_height() + 2,
+          "up to the cap, past which the list scrolls");
+    if (split != nullptr) split->set_position(emptySplit + 20);
+    pump();
+    addFromMenu(*add, effects.front()->title());
+    pump();
+    check(split != nullptr && split->get_position() == emptySplit + 20,
+          "once dragged, the split stays put as the chain grows");
+
+    // With the split dragged all the way down, the button must still work.
+    if (split != nullptr) split->set_position(10000);
+    pump();
+    add->popup();
+    pump();
+    check(menu->get_mapped(), "the menu opens with the split dragged to the bottom");
+    add->popdown();
+    pump();
+}
+
+// The labels of the entries under the "Open Recent" submenu of `model`, or
+// nothing when there is no such submenu.
+void recentLabels(GMenuModel* model, std::vector<std::string>& out, bool& found) {
+    for (int i = 0; i < g_menu_model_get_n_items(model); ++i) {
+        char* label = nullptr;
+        g_menu_model_get_item_attribute(model, i, G_MENU_ATTRIBUTE_LABEL, "s", &label);
+        const std::string text = label != nullptr ? label : "";
+        g_free(label);
+        if (GMenuModel* section = g_menu_model_get_item_link(model, i, G_MENU_LINK_SECTION)) {
+            recentLabels(section, out, found);
+            g_object_unref(section);
+        }
+        if (GMenuModel* submenu = g_menu_model_get_item_link(model, i, G_MENU_LINK_SUBMENU)) {
+            if (text == "Open Recent") {
+                found = true;
+                for (int j = 0; j < g_menu_model_get_n_items(submenu); ++j) {
+                    char* entry = nullptr;
+                    g_menu_model_get_item_attribute(submenu, j, G_MENU_ATTRIBUTE_LABEL, "s", &entry);
+                    out.emplace_back(entry != nullptr ? entry : "");
+                    g_free(entry);
+                }
+            }
+            g_object_unref(submenu);
+        }
+    }
+}
+
+std::vector<std::string> recentEntries(Gtk::Window& window) {
+    std::vector<Gtk::MenuButton*> buttons;
+    collect<Gtk::MenuButton>(window, [](Gtk::MenuButton& b) { return b.get_tooltip_text() == "Project menu"; },
+                             buttons);
+    std::vector<std::string> labels;
+    bool found = false;
+    if (buttons.empty()) return labels;
+    auto* popover = dynamic_cast<Gtk::PopoverMenu*>(buttons.front()->get_popover());
+    if (popover == nullptr || !popover->get_menu_model()) return labels;
+    recentLabels(popover->get_menu_model()->gobj(), labels, found);
+    if (!found) labels.emplace_back("<no Open Recent submenu>");
+    return labels;
+}
+
+// The version and the changelog, each a menu entry away.
+void testHelpWindows(Gtk::Window& window) {
+    std::cout << "changelog and about\n";
+    auto toplevel = [](const std::string& title) -> Gtk::Window* {
+        for (auto* w : Gtk::Window::list_toplevels()) {
+            if (w->get_title() == title && w->get_visible()) return w;
+        }
+        return nullptr;
+    };
+
+    window.activate_action("win.show-changelog");
+    pump(200);
+    auto* changelog = toplevel("Changelog");
+    check(changelog != nullptr, "Changelog opens a window");
+    auto* text = changelog != nullptr ? named<Gtk::TextView>(*changelog, "changelog") : nullptr;
+    const std::string shown = text != nullptr ? std::string(text->get_buffer()->get_text()) : "";
+    check(shown.find(std::string(effector::kVersion) + " — ") != std::string::npos,
+          "listing this version as a release");
+    check(shown.find("[") == std::string::npos && shown.find("`") == std::string::npos &&
+              shown.find("### ") == std::string::npos,
+          "with the Markdown laid out rather than shown");
+    if (changelog != nullptr) changelog->close();
+    pump(50);
+    check(toplevel("Changelog") == nullptr, "and closes");
+
+    window.activate_action("win.about");
+    pump(200);
+    Gtk::AboutDialog* about = nullptr;
+    for (auto* w : Gtk::Window::list_toplevels()) {
+        if (auto* dialog = dynamic_cast<Gtk::AboutDialog*>(w); dialog != nullptr && dialog->get_visible()) {
+            about = dialog;
+        }
+    }
+    check(about != nullptr && about->get_version() == std::string(effector::kVersion),
+          "About Effector shows the version");
+    if (about != nullptr) about->close();
+    pump(50);
+}
+
+void testRecentProjects(Gtk::Window& window, const std::filesystem::path& dir) {
+    std::cout << "recent projects\n";
+    check(recentEntries(window) == std::vector<std::string>{"No Recent Projects"},
+          "Open Recent starts out empty");
+
+    // Two projects of the same name in different folders, and a third.
+    std::filesystem::create_directories(dir / "first");
+    std::filesystem::create_directories(dir / "second");
+    const std::filesystem::path paths[] = {dir / "first" / "my_look.json", dir / "second" / "my_look.json",
+                                           dir / "other.json"};
+    effector::Project project;
+    project.stages.push_back({effector::effectByName("blur"), {}});  // renders with no sources
+    for (const auto& path : paths) {
+        effector::saveProject(path.string(), project);
+        window.activate_action("win.open-recent",
+                               Glib::Variant<Glib::ustring>::create(Glib::filename_to_uri(path.string())));
+        pump(50);
+    }
+    pump(500);  // the recent list is written, and announced, from an idle
+    check(window.get_title() == "other — Effector", "an entry opens its project");
+    const auto labels = recentEntries(window);
+    check(labels == std::vector<std::string>{"other", "my__look (second)", "my__look (first)"},
+          "opened projects are listed newest first, a shared name with its folder");
+}
+
+}  // namespace
+
+int main(int argc, char** argv) {
+    // A crash should still leave every check before it on the screen.
+    std::cout << std::unitbuf;
+    const char* x11 = std::getenv("DISPLAY");
+    const char* wayland = std::getenv("WAYLAND_DISPLAY");
+    if ((x11 == nullptr || *x11 == '\0') && (wayland == nullptr || *wayland == '\0')) {
+        std::cout << "no display, skipped\n";
+        return 77;
+    }
+
+    // Keep the projects the tests open out of the user's own recent list.
+    std::string dataTemplate = (std::filesystem::temp_directory_path() / "effector-gui-XXXXXX").string();
+    const std::filesystem::path dataDir = g_mkdtemp(dataTemplate.data());
+    g_setenv("XDG_DATA_HOME", dataDir.c_str(), TRUE);
+
+    auto app = Gtk::Application::create("org.effector.GuiTests",
+                                        Gio::Application::Flags::NON_UNIQUE);
+    app->signal_activate().connect([&app, &dataDir] {
+        auto window = std::make_unique<effector::EffectorWindow>(effector::Options{});
+        app->add_window(*window);
+        window->present();
+        pump(300);
+        runTests(*window);
+        testHelpWindows(*window);
+        testRecentProjects(*window, dataDir / "projects");
+        app->remove_window(*window);
+    });
+    const int status = app->run(argc > 0 ? 1 : 0, argv);
+    std::filesystem::remove_all(dataDir);
+    if (status != 0) return status;
+    std::cout << (failures == 0 ? "all passed\n" : std::to_string(failures) + " failed\n");
+    return failures;
+}