Merge branch 'chaos-effects'

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,

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/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

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";
@@ -933,6 +955,150 @@ 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)};