Keep the status line short, with the full chain and setup in its tooltip

The line now reads only the number of effects that ran and the render
time; the chain, canvas size, sources and seed move to the tooltip.

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

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
@@ -20,6 +20,13 @@ 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
@@ -148,8 +155,9 @@ is discarded rather than mixed into the new project (`dropLoadedImages_`).
 
 `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
+no display) + Threads — **no gtkmm, no display**. `effector_gui` (static) adds
-adds `src/main.cpp`, `src/cli/`, `src/gui/` and links gtkmm. Keep GTK out of
+`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

@@ -32,13 +32,21 @@ add_library(effector_core STATIC
     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)
 # The core is GUI-free: it only needs gdk-pixbuf for decoding and encoding,
@@ -46,14 +54,18 @@ target_include_directories(effector_core PUBLIC src)
 target_link_libraries(effector_core PUBLIC PkgConfig::GDKPIXBUF PkgConfig::PANGOCAIRO Threads::Threads)
 target_compile_options(effector_core PRIVATE -Wall -Wextra -Wpedantic)
 
-# --- application --------------------------------------------------------------
+# --- interface: the GTK window, split out so the GUI tests can link it --------
-add_executable(effector
+add_library(effector_gui STATIC
-    src/main.cpp
     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)

src/core/effect.hpp

@@ -38,6 +38,13 @@ public:
     // 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/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/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/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"
@@ -57,6 +58,10 @@ 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.")
             .styled(),
@@ -198,6 +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.");
@@ -264,6 +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

@@ -30,6 +30,8 @@ public:
     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.cpp

@@ -43,6 +43,40 @@ Gtk::Label* sectionLabel(const char* text) {
     return label;
 }
 
+// A GtkSpinButton takes every wheel turn over it: it grabs the focus and
+// spins its value, so scrolling down a column of params stops dead at the
+// first spin under the pointer and quietly changes it. This hands the wheel to
+// the view instead unless the spin already has the focus -- the user clicked
+// into it and means to adjust it. It runs in the capture phase, ahead of the
+// spin's own controller, and so has to scroll the enclosing ScrolledWindow
+// itself: stopping the event there stops it for the window as well.
+void scrollPastUnlessFocused(Gtk::SpinButton& spin) {
+    auto scroll = Gtk::EventControllerScroll::create();
+    scroll->set_propagation_phase(Gtk::PropagationPhase::CAPTURE);
+    scroll->set_flags(Gtk::EventControllerScroll::Flags::VERTICAL);
+    auto* controller = scroll.get();
+    scroll->signal_scroll().connect(
+        [&spin, controller](double, double dy) {
+            if ((spin.get_state_flags() & Gtk::StateFlags::FOCUS_WITHIN) == Gtk::StateFlags::FOCUS_WITHIN) {
+                return false;
+            }
+            auto* scroller = spin.get_ancestor(GTK_TYPE_SCROLLED_WINDOW);
+            if (scroller == nullptr) return true;
+            auto adjustment = static_cast<Gtk::ScrolledWindow*>(scroller)->get_vadjustment();
+            // The step a ScrolledWindow itself takes for one notch of a wheel;
+            // a touchpad already reports its deltas in pixels.
+            double step = dy;
+            if (controller->get_unit() == Gdk::ScrollUnit::WHEEL) {
+                step *= std::pow(adjustment->get_page_size(), 2.0 / 3.0);
+            }
+            adjustment->set_value(std::clamp(adjustment->get_value() + step, adjustment->get_lower(),
+                                             adjustment->get_upper() - adjustment->get_page_size()));
+            return true;
+        },
+        false);
+    spin.add_controller(scroll);
+}
+
 }  // namespace
 
 EffectorWindow::EffectorWindow(const Options& initial) {
@@ -73,6 +107,7 @@ EffectorWindow::EffectorWindow(const Options& initial) {
 
 EffectorWindow::~EffectorWindow() {
     debounce_.disconnect();
+    chainSplitFit_.disconnect();
     loadWindowDelay_.disconnect();
     loadCancel_.store(true, std::memory_order_relaxed);
     if (loader_.joinable()) loader_.join();
@@ -118,29 +153,137 @@ void EffectorWindow::buildUi() {
     root->append(*paned);
 }
 
-// The chain is what the interface is about, so it comes first and the params
+// The sidebar is two tabs. "Chain" is what the interface is about: the stages
-// of the selected stage sit right below it. The sources are a prerequisite,
+// and the params of the selected one, with the whole height to themselves.
-// not the subject: they live at the bottom in a collapsed expander.
+// "Setup" holds what is set once per project -- the sources, the canvas and
+// the seed -- so it never takes room from the chain however long that grows.
 Gtk::Widget& EffectorWindow::buildSidebar() {
+    auto* stack = Gtk::make_managed<Gtk::Stack>();
+    stack->set_vexpand(true);
+    stack->set_transition_type(Gtk::StackTransitionType::CROSSFADE);
+    stack->add(buildChainTab(), "chain", "Chain");
+    stack->add(buildSetupTab(), "setup", "Setup");
+
+    auto* switcher = Gtk::make_managed<Gtk::StackSwitcher>();
+    switcher->set_stack(*stack);
+    switcher->set_halign(Gtk::Align::CENTER);
+
     auto* sidebar = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 12);
     sidebar->set_margin(12);
+    sidebar->append(*switcher);
+    sidebar->append(*stack);
+    return *sidebar;
+}
 
-    sidebar->append(buildChainSection());
+// The chain and the params of the selected stage share the tab through a
+// split. Until the user drags it, the split rests under the chain's rows
+// (fitChainSplit), so a short chain leaves the tab to the params and a long
+// one grows up to chainListMaxHeight and then scrolls; once dragged, it stays
+// where it was put.
+// The tallest the chain list grows on its own before it scrolls, in pixels:
+// room for eight stages.
+constexpr int chainListMaxHeight = 270;
 
+Gtk::Widget& EffectorWindow::buildChainTab() {
+    auto* params = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 12);
+    params->set_margin_top(12);
     paramHeading_.set_xalign(0.0F);
     paramHeading_.add_css_class("heading");
-    sidebar->append(paramHeading_);
+    params->append(paramHeading_);
     paramGrid_.set_column_spacing(8);
     paramGrid_.set_row_spacing(6);
     auto* paramScroller = Gtk::make_managed<Gtk::ScrolledWindow>();
     paramScroller->set_policy(Gtk::PolicyType::NEVER, Gtk::PolicyType::AUTOMATIC);
     paramScroller->set_child(paramGrid_);
     paramScroller->set_vexpand(true);
-    sidebar->append(*paramScroller);
+    params->append(*paramScroller);
+
+    auto& chain = buildChainSection();
+    chain.set_margin_bottom(6);
+
+    auto* split = Gtk::make_managed<Gtk::Paned>(Gtk::Orientation::VERTICAL);
+    split->set_start_child(chain);
+    split->set_end_child(*params);
+    split->set_resize_start_child(false);
+    split->set_resize_end_child(true);
+    split->set_shrink_start_child(false);
+    split->set_shrink_end_child(false);
+    chainSplit_ = split;
+    split->property_position().signal_changed().connect([this] { onChainSplitMoved(); });
+    // The room the split has changes with the window, and a fit it had to
+    // clamp may fit whole now.
+    split->property_max_position().signal_changed().connect([this] { scheduleChainSplitFit(); });
+    // A double-click on the handle undoes the drag: the split fits the rows
+    // again, and follows them from then on. The handle is the one child of the
+    // split that is neither pane, but the click is heard on the split itself,
+    // grouped with the split's own drag: that drag claims every press on the
+    // handle, which would cancel a click gesture anywhere else.
+    Gtk::Widget* handle = nullptr;
+    for (auto* child = split->get_first_child(); child != nullptr; child = child->get_next_sibling()) {
+        if (child != &chain && child != params) handle = child;
+    }
+    if (handle != nullptr) {
+        handle->set_tooltip_text("Drag to share the room, double-click to fit the chain");
+        auto click = Gtk::GestureClick::create();
+        click->set_propagation_phase(Gtk::PropagationPhase::CAPTURE);
+        // The split's drag ends every press on the handle, which starts the
+        // click's count over, so the second press is counted here. And that
+        // drag is still going on during the second press -- the least jitter
+        // puts the handle back under the pointer -- so the fit waits for it
+        // to end.
+        std::vector<Glib::RefPtr<Gtk::GestureDrag>> drags;
+        const auto controllers = split->observe_controllers();
+        for (guint i = 0; i < controllers->get_n_items(); ++i) {
+            auto other = std::dynamic_pointer_cast<Gtk::Gesture>(controllers->get_object(i));
+            if (other) click->group(other);
+            if (auto drag = std::dynamic_pointer_cast<Gtk::GestureDrag>(other)) drags.push_back(drag);
+        }
+        auto lastPress = std::make_shared<guint32>(0);
+        auto refitPending = std::make_shared<bool>(false);
+        for (const auto& drag : drags) {
+            drag->signal_drag_end().connect([this, refitPending](double, double) {
+                if (!*refitPending) return;
+                *refitPending = false;
+                refitChainSplit();
+            });
+        }
+        auto* gesture = click.get();  // not the RefPtr: the gesture owns this slot
+        const bool waitForDrag = !drags.empty();
+        click->signal_pressed().connect(
+            [this, split, handle, gesture, lastPress, refitPending, waitForDrag](int, double x, double y) {
+            // The handle is thin, and the drag takes presses a little past it.
+            const auto bounds = handle->compute_bounds(*split);
+            constexpr double slack = 6.0;
+            if (!bounds || y < bounds->get_y() - slack ||
+                y > bounds->get_y() + bounds->get_height() + slack ||
+                x < bounds->get_x() || x > bounds->get_x() + bounds->get_width()) {
+                *lastPress = 0;
+                return;
+            }
+            const guint32 now = gesture->get_current_event_time();
+            const int doubleClick = Gtk::Settings::get_default()->property_gtk_double_click_time();
+            if (*lastPress != 0 && now - *lastPress <= static_cast<guint32>(doubleClick)) {
+                *lastPress = 0;
+                if (waitForDrag) {
+                    *refitPending = true;
+                } else {
+                    refitChainSplit();
+                }
+            } else {
+                *lastPress = now;
+            }
+        });
+        split->add_controller(click);
+    }
     rebuildChainRows();
     buildParamWidgets();
+    return *split;
+}
 
-    sidebar->append(*Gtk::make_managed<Gtk::Separator>(Gtk::Orientation::HORIZONTAL));
+// The sources come first because they are the first thing a project needs;
+// their list takes whatever height the canvas and seed leave over.
+Gtk::Widget& EffectorWindow::buildSetupTab() {
+    auto* tab = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 12);
 
     sourceList_.set_selection_mode(Gtk::SelectionMode::NONE);
     sourceList_.add_css_class("boxed-list");
@@ -153,10 +296,16 @@ Gtk::Widget& EffectorWindow::buildSidebar() {
     scroller->set_policy(Gtk::PolicyType::NEVER, Gtk::PolicyType::AUTOMATIC);
     scroller->set_child(sourceList_);
     scroller->set_size_request(-1, 140);
-    scroller->set_margin_top(6);
+    scroller->set_vexpand(true);
 
-    auto* sourcesBox = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 6);
+    sourcesHeading_.set_xalign(0.0F);
-    sourcesBox->append(*scroller);
+    sourcesHeading_.add_css_class("heading");
+    sourcesSection_.set_name("sources");
+    sourcesSection_.set_orientation(Gtk::Orientation::VERTICAL);
+    sourcesSection_.set_spacing(6);
+    sourcesSection_.set_vexpand(true);
+    sourcesSection_.append(sourcesHeading_);
+    sourcesSection_.append(*scroller);
 
     // Same shape as "Add effect": the icon and the text are put together by
     // hand because set_label() and set_icon_name() replace one another.
@@ -169,16 +318,14 @@ Gtk::Widget& EffectorWindow::buildSidebar() {
     addButton->set_halign(Gtk::Align::START);
     addButton->set_tooltip_text("Add source images");
     addButton->signal_clicked().connect(sigc::mem_fun(*this, &EffectorWindow::onAddImages));
-    sourcesBox->append(*addButton);
+    sourcesSection_.append(*addButton);
     addButton_ = addButton;
 
-    sourcesExpander_.set_child(*sourcesBox);
-    sourcesExpander_.set_expanded(false);
     updateSourcesLabel();
-    sidebar->append(sourcesExpander_);
+    tab->append(sourcesSection_);
 
-    sidebar->append(*sectionLabel("Canvas"));
+    tab->append(*sectionLabel("Canvas"));
-    sidebar->append(buildCanvasSection());
+    tab->append(buildCanvasSection());
 
     auto* seedBox = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::HORIZONTAL, 8);
     auto* seedLabel = Gtk::make_managed<Gtk::Label>("Seed");
@@ -188,9 +335,9 @@ Gtk::Widget& EffectorWindow::buildSidebar() {
     seedEntry_.set_text(std::to_string(seed_));
     seedEntry_.signal_activate().connect(sigc::mem_fun(*this, &EffectorWindow::onSeedEntered));
     seedBox->append(seedEntry_);
-    sidebar->append(*seedBox);
+    tab->append(*seedBox);
 
-    return *sidebar;
+    return *tab;
 }
 
 // Only the first stage is ever handed the sources, so whether the chain wants
@@ -199,15 +346,14 @@ Gtk::Widget& EffectorWindow::buildSidebar() {
 // rather than left there to be filled in vain. This is the same declarative
 // answer the render gate uses -- no effect is named here.
 void EffectorWindow::updateSourcesVisible() {
-    sourcesExpander_.set_visible(chainNeedsSources(stages_));
+    sourcesSection_.set_visible(chainNeedsSources(stages_));
 }
 
-// The expander is collapsed by default, so its label carries the count that
+// The heading carries the count, which a long list scrolled away would hide.
-// used to be plain to see in the list.
 void EffectorWindow::updateSourcesLabel() {
     int count = 0;
     while (sourceList_.get_row_at_index(count) != nullptr) ++count;
-    sourcesExpander_.set_label(count == 0 ? "Source images"
+    sourcesHeading_.set_text(count == 0 ? "Source images"
                                           : "Source images (" + std::to_string(count) + ")");
 }
 
@@ -244,6 +390,7 @@ Gtk::Widget& EffectorWindow::buildCanvasSection() {
     dpiSpin_.set_value(kDefaultDpi);
     for (auto* spin : {&widthSpin_, &heightSpin_, &dpiSpin_}) {
         spin->set_hexpand(true);
+        scrollPastUnlessFocused(*spin);
     }
     for (auto* spin : {&widthSpin_, &heightSpin_}) {
         spin->signal_value_changed().connect([this] {
@@ -331,7 +478,7 @@ Gtk::Widget& EffectorWindow::buildPreview() {
     picture_.set_can_shrink(true);
     picture_.set_content_fit(Gtk::ContentFit::CONTAIN);
 
-    placeholder_.set_text("Add source images to start.");
+    placeholder_.set_text("Add source images under Setup to start.");
     placeholder_.set_wrap(true);
     placeholder_.add_css_class("dim-label");
 
@@ -350,6 +497,12 @@ Gtk::Widget& EffectorWindow::buildPreview() {
 
     auto* box = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL);
     box->append(*overlay);
+    // A long chain makes a long status line; left to its natural width it
+    // would widen the preview column past the pane and push the picture off
+    // centre. Ellipsized, it never asks for more room than it is given.
+    status_.set_ellipsize(Pango::EllipsizeMode::END);
+    status_.set_margin_start(8);
+    status_.set_margin_end(8);
     status_.set_margin_top(6);
     status_.set_margin_bottom(8);
     status_.add_css_class("dim-label");
@@ -434,6 +587,7 @@ void EffectorWindow::buildParamWidgets() {
                                     : paramDouble(values, spec.key, spec.defaultValue));
                 spin->signal_value_changed().connect(
                     sigc::mem_fun(*this, &EffectorWindow::onParamChanged));
+                scrollPastUnlessFocused(*spin);
                 widget = std::move(spin);
                 break;
             }
@@ -1129,10 +1283,44 @@ void EffectorWindow::onImagesChosen(const Glib::RefPtr<Gio::AsyncResult>& result
 
 // ---------------------------------------------------------------- chain ---
 
-Gtk::Widget& EffectorWindow::buildChainSection() {
+// The move and remove buttons are faded out until the pointer is over their
-    auto* box = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 6);
+// row, or the row is selected or focused, so a long chain reads as a list of
-    box->append(*sectionLabel("Effect chain"));
+// names rather than a column of icons. They keep their place while hidden,
+// so the names do not jump as the pointer moves.
+const char* const stageRowCss = R"css(
+row.stage-row .stage-action {
+    min-width: 24px;
+    min-height: 24px;
+    padding: 0;
+    opacity: 0;
+    transition: opacity 120ms;
+}
+row.stage-row:hover .stage-action,
+row.stage-row:selected .stage-action,
+row.stage-row:focus-within .stage-action {
+    opacity: 1;
+}
+)css";
 
+Gtk::Widget& EffectorWindow::buildChainSection() {
+    auto css = Gtk::CssProvider::create();
+    css->load_from_string(stageRowCss);
+    Gtk::StyleProvider::add_provider_for_display(Gdk::Display::get_default(), css,
+                                                 GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
+
+    auto* box = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::VERTICAL, 6);
+
+    // "Add effect" sits beside the heading rather than under the list: under
+    // it, the split could drag it so far down the screen that the menu of
+    // effects had no room left to open.
+    auto* heading = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::HORIZONTAL, 6);
+    auto* title = sectionLabel("Effect chain");
+    title->set_hexpand(true);
+    heading->append(*title);
+    heading->append(addEffectButton_);
+    box->append(*heading);
+
+    chainList_.set_name("chain-list");
     chainList_.add_css_class("boxed-list");
     chainList_.set_selection_mode(Gtk::SelectionMode::SINGLE);
     auto* empty = Gtk::make_managed<Gtk::Label>("No effects yet");
@@ -1145,7 +1333,13 @@ Gtk::Widget& EffectorWindow::buildChainSection() {
     auto* scroller = Gtk::make_managed<Gtk::ScrolledWindow>();
     scroller->set_policy(Gtk::PolicyType::NEVER, Gtk::PolicyType::AUTOMATIC);
     scroller->set_child(chainList_);
-    scroller->set_size_request(-1, 150);
+    // The list asks for the height of its rows, up to a cap, which is where
+    // the split above the params rests until it is dragged; the size request
+    // is only the least it may be dragged down to.
+    scroller->set_propagate_natural_height(true);
+    scroller->set_max_content_height(chainListMaxHeight);
+    scroller->set_size_request(-1, 100);
+    scroller->set_vexpand(true);
     box->append(*scroller);
 
     // set_label() and set_icon_name() replace one another, so the icon and the
@@ -1158,12 +1352,14 @@ Gtk::Widget& EffectorWindow::buildChainSection() {
     addEffectButton_.set_always_show_arrow(true);
     addEffectButton_.set_tooltip_text("Append an effect, applied to the output so far");
     addEffectButton_.set_popover(static_cast<Gtk::Popover&>(buildAddMenu()));
-    addEffectButton_.set_halign(Gtk::Align::START);
+    addEffectButton_.set_name("add-effect");
-    box->append(addEffectButton_);
 
     return *box;
 }
 
+// The tallest the menu of effects grows before it scrolls, in pixels.
+constexpr int addMenuMaxHeight = 480;
+
 // One entry per registered effect, so a new effect shows up here without this
 // file knowing anything about it.
 Gtk::Widget& EffectorWindow::buildAddMenu() {
@@ -1182,7 +1378,15 @@ Gtk::Widget& EffectorWindow::buildAddMenu() {
         list->append(*item);
     }
 
-    popover->set_child(*list);
+    // A popover that does not fit on the screen is not shown at all, and the
+    // list grows with every effect registered, so past a point it scrolls.
+    auto* scroller = Gtk::make_managed<Gtk::ScrolledWindow>();
+    scroller->set_policy(Gtk::PolicyType::NEVER, Gtk::PolicyType::AUTOMATIC);
+    scroller->set_propagate_natural_height(true);
+    scroller->set_max_content_height(addMenuMaxHeight);
+    scroller->set_child(*list);
+
+    popover->set_child(*scroller);
     return *popover;
 }
 
@@ -1223,6 +1427,7 @@ void EffectorWindow::rebuildChainRows() {
     // Only the rows: the placeholder is a child of the list box as well, and
     // removing it would leave the empty list blank.
     while (auto* row = chainList_.get_row_at_index(0)) chainList_.remove(*row);
+    stageLabels_.clear();
 
     // The first stage that actually runs is the one handed the sources, which
     // is not stage 1 once stage 1 is switched off.
@@ -1233,9 +1438,10 @@ void EffectorWindow::rebuildChainRows() {
     for (std::size_t i = 0; i < stages_.size(); ++i) {
         const int index = static_cast<int>(i);
         auto* row = Gtk::make_managed<Gtk::ListBoxRow>();
-        auto* box = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::HORIZONTAL, 4);
+        row->add_css_class("stage-row");
-        box->set_margin_top(4);
+        auto* box = Gtk::make_managed<Gtk::Box>(Gtk::Orientation::HORIZONTAL, 2);
-        box->set_margin_bottom(4);
+        box->set_margin_top(1);
+        box->set_margin_bottom(1);
         box->set_margin_start(8);
         box->set_margin_end(4);
 
@@ -1252,8 +1458,8 @@ void EffectorWindow::rebuildChainRows() {
         });
         box->append(*check);
 
-        auto* label = Gtk::make_managed<Gtk::Label>(std::to_string(index + 1) + ". " +
+        auto* label = Gtk::make_managed<Gtk::Label>(stageLabel(i));
-                                                    stages_[i].effect->title());
+        stageLabels_.push_back(label);
         label->set_xalign(0.0F);
         label->set_hexpand(true);
         label->set_ellipsize(Pango::EllipsizeMode::END);
@@ -1275,6 +1481,8 @@ void EffectorWindow::rebuildChainRows() {
             button->set_icon_name(action.icon);
             button->set_tooltip_text(action.tip);
             button->add_css_class("flat");
+            button->add_css_class("stage-action");
+            button->set_valign(Gtk::Align::CENTER);
             const int delta = action.delta;
             button->signal_clicked().connect([this, index, delta] {
                 if (delta == 0) {
@@ -1295,6 +1503,56 @@ void EffectorWindow::rebuildChainRows() {
     selectStage(selectedStage_);
     suspendStageSelect_ = false;
     updateSourcesVisible();
+    scheduleChainSplitFit();
+}
+
+// Once the rows are laid out, not in the middle of a rebuild or of an
+// allocation, where moving the split would ask for another one.
+void EffectorWindow::scheduleChainSplitFit() {
+    if (chainSplitDragged_ || chainSplitFit_.connected()) return;
+    chainSplitFit_ = Glib::signal_idle().connect([this] {
+        fitChainSplit();
+        return false;
+    });
+}
+
+// GtkPaned would size the fixed pane from its minimum height, which is only
+// the floor it may be dragged down to, so the fit to the rows' natural height
+// is done here.
+void EffectorWindow::fitChainSplit() {
+    if (chainSplit_ == nullptr || chainSplitDragged_) return;
+    auto* chain = chainSplit_->get_start_child();
+    if (chain == nullptr) return;
+    int minimum = 0;
+    int natural = 0;
+    int minimumBaseline = 0;
+    int naturalBaseline = 0;
+    const int width = chainSplit_->get_width();
+    chain->measure(Gtk::Orientation::VERTICAL, width > 0 ? width : -1, minimum, natural,
+                   minimumBaseline, naturalBaseline);
+    fittedChainSplit_ = natural;
+    suspendSplitTrack_ = true;
+    chainSplit_->set_position(natural);
+    suspendSplitTrack_ = false;
+}
+
+void EffectorWindow::refitChainSplit() {
+    chainSplitDragged_ = false;
+    fitChainSplit();
+}
+
+// Any move but a fit, or GTK clamping a fit into a window too short for it,
+// is the user's drag.
+void EffectorWindow::onChainSplitMoved() {
+    if (suspendSplitTrack_ || fittedChainSplit_ < 0) return;
+    const int position = chainSplit_->get_position();
+    if (position == fittedChainSplit_) return;
+    const int lowest = chainSplit_->property_min_position();
+    const int highest = chainSplit_->property_max_position();
+    if (fittedChainSplit_ > highest && position == highest) return;
+    if (fittedChainSplit_ < lowest && position == lowest) return;
+    chainSplitDragged_ = true;
+    chainSplitFit_.disconnect();
 }
 
 // Switching a stage off leaves everything about it alone -- its settings, its
@@ -1325,8 +1583,17 @@ void EffectorWindow::onStageSelected() {
 
 // ------------------------------------------------------------ rendering ---
 
+std::string EffectorWindow::stageLabel(std::size_t index) const {
+    const ChainStage& stage = stages_[index];
+    return std::to_string(index + 1) + ". " + stage.effect->label(stageValues(stage, styles_));
+}
+
 void EffectorWindow::onParamChanged() {
     storeParams();
+    // A param can be what names the stage (the words of a text stage), and a
+    // styled one can rename every stage sharing the style.
+    for (std::size_t i = 0; i < stageLabels_.size() && i < stages_.size(); ++i)
+        stageLabels_[i]->set_text(stageLabel(i));
     requestRender();
 }
 
@@ -1391,7 +1658,7 @@ bool EffectorWindow::canRender() const {
 std::string EffectorWindow::missingText() const {
     if (stages_.empty()) return "Add an effect to start.";
     if (enabledStages(stages_).empty()) return "Every effect is switched off.";
-    return "Add source images to start.";
+    return "Add source images under Setup to start.";
 }
 
 void EffectorWindow::showPlaceholder() {
@@ -1400,6 +1667,7 @@ void EffectorWindow::showPlaceholder() {
     placeholder_.set_text(missingText());
     previewStack_.set_visible_child("placeholder");
     status_.set_text("");
+    status_.set_tooltip_text("");
 }
 
 void EffectorWindow::requestRender() {
@@ -1496,15 +1764,20 @@ void EffectorWindow::onRenderFinished() {
     previewStack_.set_visible_child("picture");
     saveButton_.set_sensitive(true);
 
+    // The line itself stays short; the full chain and setup go in the tooltip.
+    const std::size_t effects = enabledStages(stages_).size();
     std::ostringstream status;
     status.setf(std::ios::fixed);
     status.precision(1);
-    status << chainTitle(stages_) << " · " << result_.width() << "×" << result_.height() << " · ";
+    status << effects << (effects == 1 ? " effect" : " effects") << " · " << millis << " ms";
+    std::ostringstream details;
+    details << chainTitle(stages_) << " · " << result_.width() << "×" << result_.height() << " · ";
     if (!sources_->empty()) {
-        status << sources_->size() << (sources_->size() == 1 ? " source" : " sources") << " · ";
+        details << sources_->size() << (sources_->size() == 1 ? " source" : " sources") << " · ";
     }
-    status << "seed " << seed_ << " · " << millis << " ms";
+    details << "seed " << seed_;
     status_.set_text(status.str());
+    status_.set_tooltip_text(details.str());
 }
 
 // -------------------------------------------------------------- project ---
@@ -1679,6 +1952,7 @@ void EffectorWindow::writeProject(const std::string& path) {
     projectPath_ = path;
     updateTitle();
     status_.set_text("Saved " + path);
+    status_.set_tooltip_text("Saved " + path);
 }
 
 void EffectorWindow::updateTitle() {
@@ -1722,6 +1996,7 @@ void EffectorWindow::onSaveChosen(const Glib::RefPtr<Gio::AsyncResult>& result,
     }
     clearError();
     status_.set_text("Saved " + path.string());
+    status_.set_tooltip_text("Saved " + path.string());
 }
 
 // --------------------------------------------------------------- errors ---

src/gui/window.hpp

@@ -29,6 +29,8 @@ public:
 private:
     void buildUi();
     Gtk::Widget& buildSidebar();
+    Gtk::Widget& buildChainTab();
+    Gtk::Widget& buildSetupTab();
     Gtk::Widget& buildPreview();
     void buildParamWidgets();
     ParamValues paramValues() const;
@@ -72,7 +74,7 @@ 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();
 
@@ -93,6 +95,12 @@ private:
     // 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
@@ -143,6 +151,15 @@ private:
     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
@@ -183,7 +200,8 @@ private:
     std::unique_ptr<Gtk::Window> loadWindow_;
     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_;

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

@@ -12,6 +12,7 @@
 #include <locale>
 #include <mutex>
 #include <optional>
+#include <set>
 #include <string>
 #include <utility>
 #include <vector>
@@ -201,6 +202,18 @@ 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;
@@ -243,6 +256,15 @@ 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";
@@ -737,6 +759,20 @@ 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;
@@ -821,6 +857,13 @@ 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");
@@ -855,7 +898,8 @@ int main() {
                   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_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");
@@ -933,6 +977,150 @@ int main() {
               "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)};

tests/gui_tests.cpp

@@ -0,0 +1,300 @@
+// 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 <iostream>
+#include <memory>
+#include <string>
+#include <thread>
+#include <vector>
+
+#include "cli/options.hpp"
+#include "core/registry.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;
+}
+
+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 << "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();
+}
+
+}  // 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;
+    }
+
+    auto app = Gtk::Application::create("org.effector.GuiTests",
+                                        Gio::Application::Flags::NON_UNIQUE);
+    app->signal_activate().connect([&app] {
+        auto window = std::make_unique<effector::EffectorWindow>(effector::Options{});
+        app->add_window(*window);
+        window->present();
+        pump(300);
+        runTests(*window);
+        app->remove_window(*window);
+    });
+    const int status = app->run(argc > 0 ? 1 : 0, argv);
+    if (status != 0) return status;
+    std::cout << (failures == 0 ? "all passed\n" : std::to_string(failures) + " failed\n");
+    return failures;
+}