License Effector under the GPL, version 3 or later

LICENSE holds the text, the README and About Effector state it, and the
Arch package declares it. The version moves to 0.5.2 for the release.

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

.gitignore

@@ -5,3 +5,7 @@ compile_commands.json
 __pycache__/
 *.o
 *.a
+packaging/arch/effector/
+packaging/arch/src/
+packaging/arch/pkg/
+packaging/arch/*.pkg.tar*

CHANGELOG.md

@@ -0,0 +1,86 @@
+# Changelog
+
+Every release of Effector, newest first. The version lives in one place, the
+`project()` line of `CMakeLists.txt`, and each release is a `vX.Y.Z` tag on the
+commit that made it. The interface shows this file under Changelog in its menu.
+
+## [0.5.2] - 2026-09-26
+
+### Changed
+- Effector is free software under the GNU General Public License, version 3
+  or later; the `LICENSE` file holds the text, and About Effector says so.
+
+## [0.5.1] - 2026-09-26
+
+### Added
+- An Arch Linux `PKGBUILD` in `packaging/arch`: `makepkg -si` there builds and
+  installs the tagged release with pacman.
+- A desktop entry, so an installed Effector shows up in the app menu.
+
+## [0.5.0] - 2026-09-26
+
+### Added
+- A version number: `effector --version` prints it, and About Effector in the
+  menu shows it.
+- This changelog, readable from the interface under Changelog in the menu.
+- Open Recent in the project menu, listing the projects opened or saved here.
+- An optional shadow or glow under the image overlay, with an offset, size,
+  spread, colour and opacity.
+- Reordering the chain by dragging a row.
+
+### Fixed
+- The params' scrollbar no longer covers the spin buttons.
+
+## [0.4.0] - 2026-09-23
+
+### Added
+- Eight chaotic effects: slit shift, channel split, pixel sort, corruption,
+  shatter, warp, bit crush and feedback. None needs sources, so any of them can
+  lead a chain.
+- The sidebar split into Chain and Setup tabs.
+- A rotation for the text effect's placement.
+- Text stages labelled in the chain list with their words.
+
+### Changed
+- The preview stays centred however long the status line gets.
+- The status line stays short, with the full chain and setup in its tooltip.
+- The chain/params split fits the chain's rows until it is dragged; a
+  double-click on the handle fits it again.
+- The mouse wheel scrolls past spin buttons that do not have the focus.
+
+## [0.3.0] - 2026-09-19
+
+### Added
+- Named styles: several text stages can share one font and colour, and editing
+  the style moves every stage that follows it.
+- Switching a chain stage off without taking it apart, in the interface and
+  with `--disable NAME` on the command line.
+
+### Changed
+- The interface opens on an empty chain, and shows the sources only when the
+  chain uses them.
+
+## [0.2.0] - 2026-09-18
+
+### Added
+- Effect chains: stages cascade, each handed the previous one's output, built in
+  the sidebar or with repeated `-e`.
+- Blur, film grain, black and white, image overlay, text and tiles effects.
+- Projects saved and opened as plain JSON.
+- Standard web and print canvas formats (`--format`, `--dpi`).
+- Effects declare whether they need source images, so a chain led by blur
+  renders with none loaded.
+
+### Changed
+- The chain comes first in the sidebar.
+
+### Fixed
+- The canvas size is checked before it is narrowed to an int.
+- Projects are written and read in the C locale, and keep the seed whole.
+
+## [0.1.0] - 2026-09-18
+
+### Added
+- The C++20 port of the Python prototype: a GTK 4 interface and a headless
+  command line over pluggable effects, starting with scanlines.
+- Source images load in the background, with a progress window and Cancel.

CLAUDE.md

@@ -33,6 +33,22 @@ Headless render (no display needed, the fastest end-to-end smoke test):
 build/effector -o /tmp/out.png -s 800x600 --strip-height 6 --seed 1 a.jpg b.png
 ```
 
+### Versions and the changelog
+
+The version is the `project()` line of `CMakeLists.txt`, and nowhere else.
+CMake writes it, together with the text of `CHANGELOG.md`, into a generated
+`core/version.hpp` (`kVersion`, `kChangelog`, from `src/core/version.hpp.in`)
+in the build tree. `--version` prints it, and the header-bar menu shows it
+under About Effector and the changelog under Changelog. The `version` core test
+fails unless the newest `## [X.Y.Z]` entry in `CHANGELOG.md` is the current
+version, so a bump and its changelog entry go in together, and it also fails unless
+`pkgver` in `packaging/arch/PKGBUILD` matches (that PKGBUILD builds the
+`vX.Y.Z` tag, so reset `pkgrel=1` on a bump). Each release is an
+annotated `vX.Y.Z` tag on the commit that made it. When you add a user-visible
+change, add a line to the newest changelog entry, or start a new entry if that
+one is already tagged. The Changelog window reads only headings, `- ` bullets
+(wrapped onto indented lines) and `` `code` ``, so keep the file to those.
+
 ### Running the GUI from this shell
 
 GTK picks Wayland from an inherited `WAYLAND_DISPLAY` and will not draw into an
@@ -113,7 +129,7 @@ both the style and the stage for that reason. `renderChain` takes the pool as a
 trailing argument; the command line builds no styles and passes none.
 
 The interface builds the chain in the sidebar ("Effect chain": add from the
-menu, reorder, remove, switch off with the check on the row, one stage selected
+menu, reorder by dragging a row or with its arrows, remove, switch off with the check on the row, one stage selected
 at a time with its params below), the CLI builds it from repeated `-e`:
 `-e scanlines --strip-height 6 -e blur --radius 5`, with `--disable NAME`
 leaving a stage in place but skipping it. Flags share one namespace across all effects, so `buildChain`
@@ -148,7 +164,10 @@ can be moved or shared whole.
 
 The interface opens and saves projects from the header-bar menu (New, Open,
 Save, Save As, with the usual Ctrl+N/O/S accelerators); the window title shows
-the project name. Opening one replaces the sources, so a decode still in flight
+the project name. Open Recent lists the projects opened or saved here, kept in
+GTK's shared `RecentManager` list and told apart from other programs' files by
+the `effector` application name on each entry; the GUI tests point
+`XDG_DATA_HOME` at a temporary folder so they never touch the user's list. Opening one replaces the sources, so a decode still in flight
 is discarded rather than mixed into the new project (`dropLoadedImages_`).
 
 ### Two link targets, deliberately

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.20)
-project(effector VERSION 0.1.0 LANGUAGES CXX)
+project(effector VERSION 0.5.2 LANGUAGES CXX)
 
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
@@ -21,6 +21,14 @@ pkg_check_modules(PANGOCAIRO REQUIRED IMPORTED_TARGET pangocairo)
 
 find_package(Threads REQUIRED)
 
+# --- version: the one number, and the changelog that goes with it ------------
+# The version is the project() line above; each release is a vX.Y.Z tag on the
+# commit that set it. CHANGELOG.md is baked in so the interface can show it,
+# and editing it re-runs the configure step.
+file(READ ${CMAKE_CURRENT_SOURCE_DIR}/CHANGELOG.md EFFECTOR_CHANGELOG)
+set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS CHANGELOG.md)
+configure_file(src/core/version.hpp.in ${CMAKE_CURRENT_BINARY_DIR}/generated/core/version.hpp @ONLY)
+
 # --- core: effects and image handling, no GUI ---------------------------------
 add_library(effector_core STATIC
     src/core/canvas.cpp
@@ -48,7 +56,7 @@ add_library(effector_core STATIC
     src/effects/tiles.cpp
     src/effects/warp.cpp
 )
-target_include_directories(effector_core PUBLIC src)
+target_include_directories(effector_core PUBLIC src ${CMAKE_CURRENT_BINARY_DIR}/generated)
 # The core is GUI-free: it only needs gdk-pixbuf for decoding and encoding,
 # so headless rendering works without a display.
 target_link_libraries(effector_core PUBLIC PkgConfig::GDKPIXBUF PkgConfig::PANGOCAIRO Threads::Threads)
@@ -69,6 +77,8 @@ target_link_libraries(effector PRIVATE effector_gui)
 target_compile_options(effector PRIVATE -Wall -Wextra -Wpedantic)
 
 install(TARGETS effector RUNTIME DESTINATION bin)
+# The launcher entry, so the interface shows up in the desktop's app menu.
+install(FILES data/org.effector.Effector.desktop DESTINATION share/applications)
 
 # --- tests --------------------------------------------------------------------
 include(CTest)

LICENSE

@@ -0,0 +1,232 @@
+GNU GENERAL PUBLIC LICENSE
+Version 3, 29 June 2007
+
+Copyright © 2007 Free Software Foundation, Inc. <https://fsf.org/>
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+If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under the terms of this License, through a publicly available network server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available, or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a manner consistent with the requirements of this License, to extend the patent license to downstream recipients. “Knowingly relying” means you have actual knowledge that, but for the patent license, your conveying the covered work in a country, or your recipient's use of the covered work in a country, would infringe one or more identifiable patents in that country that you have reason to believe are valid.
+
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+
+A patent license is “discriminatory” if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007.
+
+Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law.
+
+12. No Surrender of Others' Freedom.
+If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program.
+
+13. Use with the GNU Affero General Public License.
+Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such.
+
+14. Revised Versions of this License.
+The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.
+
+Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License “or any later version” applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation.
+
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+
+Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version.
+
+15. Disclaimer of Warranty.
+THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+16. Limitation of Liability.
+IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
+
+17. Interpretation of Sections 15 and 16.
+If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee.
+
+END OF TERMS AND CONDITIONS
+
+How to Apply These Terms to Your New Programs
+
+If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
+
+To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.
+
+     <one line to give the program's name and a brief idea of what it does.>
+     Copyright (C) <year>  <name of author>
+
+     This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
+
+     This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+     You should have received a copy of the GNU General Public License along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode:
+
+     <program>  Copyright (C) <year>  <name of author>
+     This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+     This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, your program's commands might be different; for a GUI interface, you would use an “about box”.
+
+You should also get your employer (if you work as a programmer) or school, if any, to sign a “copyright disclaimer” for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see <https://www.gnu.org/licenses/>.
+
+The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read <https://www.gnu.org/philosophy/why-not-lgpl.html>.

README.md

@@ -19,12 +19,20 @@ ctest --test-dir build --output-on-failure
 The binary lands at `build/effector`; `cmake --install build --prefix ~/.local`
 installs it to `~/.local/bin`.
 
+On Arch, `packaging/arch/PKGBUILD` builds the release tagged `v<version>` from
+this repository and installs it with pacman, desktop entry included:
+
+```bash
+cd packaging/arch && makepkg -si
+```
+
 ## Run
 
 ```bash
 build/effector                  # GTK interface
 build/effector --list-effects
 build/effector --help
+build/effector --version
 ```
 
 Headless rendering, no display needed:
@@ -60,6 +68,17 @@ batch. Small batches finish before the window would be drawn, so it only appears
 if the decode is still going after 250 ms. On a terminal the headless mode keeps
 a single `reading n/total` line updated on stderr; redirected output stays clean.
 
+## Versions
+
+Releases are listed in [CHANGELOG.md](CHANGELOG.md) and tagged `vX.Y.Z`
+(`git tag -l 'v*'`). `effector --version` prints the version, and the menu in
+the interface has Changelog and About Effector.
+
+To cut a release: bump the `project()` version in `CMakeLists.txt`, move the
+changes into a new `## [X.Y.Z] - date` entry at the top of `CHANGELOG.md` (the
+core tests fail until the two agree), commit, and tag it:
+`git tag -a vX.Y.Z -m "Effector X.Y.Z"`.
+
 ## Effects
 
 ### scanlines
@@ -140,3 +159,14 @@ render time of the current preview in its status line.
 Decoding threads take the next file from a shared cursor rather than a fixed
 slice of the list, so one very large file cannot stall the files queued behind
 it and progress advances at a steady rate.
+
+## License
+
+Copyright © 2026 Si.
+
+Effector is free software: you can redistribute it and/or modify it under the
+terms of the GNU General Public License as published by the Free Software
+Foundation, either version 3 of the License, or (at your option) any later
+version. It is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; see `LICENSE` for the full text. Images you render with it are yours
+and are not covered by the license.

data/org.effector.Effector.desktop

@@ -0,0 +1,12 @@
+[Desktop Entry]
+Type=Application
+Name=Effector
+GenericName=Image Effects
+Comment=Cascade glitch and collage effects over your photographs
+Exec=effector %F
+Icon=applications-graphics
+Terminal=false
+Categories=Graphics;2DGraphics;RasterGraphics;GTK;
+MimeType=image/jpeg;image/png;image/webp;image/tiff;image/bmp;
+Keywords=glitch;collage;scanlines;photo;effect;
+StartupNotify=true

packaging/arch/PKGBUILD

@@ -0,0 +1,30 @@
+# Builds the release tagged v$pkgver from the repository this file sits in,
+# so pkgver must follow the project() line of CMakeLists.txt (the version core
+# test checks it). From this folder: makepkg -si
+pkgname=effector
+pkgver=0.5.2
+pkgrel=1
+pkgdesc='Image effects app: a GTK4 interface and a headless CLI over pluggable effects'
+arch=('x86_64' 'aarch64')
+url='https://git.plan9.uber.space/hans/effector'
+license=('GPL-3.0-or-later')
+depends=('gtkmm-4.0' 'gdk-pixbuf2' 'pango' 'cairo' 'glib2' 'glibc' 'gcc-libs')
+makedepends=('cmake' 'ninja' 'git')
+checkdepends=('xorg-server-xvfb')
+source=("$pkgname::git+file://${startdir%/packaging/arch}#tag=v$pkgver")
+sha256sums=('SKIP')
+
+build() {
+    cmake -S "$pkgname" -B build -G Ninja \
+        -DCMAKE_BUILD_TYPE=Release \
+        -DCMAKE_INSTALL_PREFIX=/usr
+    cmake --build build
+}
+
+check() {
+    ctest --test-dir build --output-on-failure
+}
+
+package() {
+    DESTDIR="$pkgdir" cmake --install build
+}

src/cli/options.cpp

@@ -61,6 +61,8 @@ Options parseOptions(int argc, char** argv) {
 
         if (arg == "-h" || arg == "--help") {
             options.showHelp = true;
+        } else if (arg == "-V" || arg == "--version") {
+            options.showVersion = true;
         } else if (arg == "--list-effects") {
             options.listEffects = true;
         } else if (arg == "-e" || arg == "--effect") {
@@ -184,6 +186,7 @@ std::string usage(const char* programName) {
         << "      --disable NAME    keep this effect in the chain but skip it\n"
         << "      --seed N          random seed (default: random)\n"
         << "      --list-effects    list available effects and exit\n"
+        << "  -V, --version         show the version and exit\n"
         << "  -h, --help            show this help and exit\n";
 
     out << "\nCanvas formats (--format):\n";

src/cli/options.hpp

@@ -27,6 +27,7 @@ struct Options {
     ParamValues params;              // only the keys the user actually passed
     bool listEffects = false;
     bool showHelp = false;
+    bool showVersion = false;
 };
 
 // Throws EffectError on bad input. Effect flags are generated from the

src/core/version.hpp.in

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

src/effects/overlay.cpp

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

src/effects/overlay.hpp

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

src/gui/window.cpp

@@ -13,6 +13,7 @@
 #include "core/project.hpp"
 #include "core/registry.hpp"
 #include "core/rng.hpp"
+#include "core/version.hpp"
 
 namespace effector {
 namespace {
@@ -21,6 +22,11 @@ const char* const kImagePatterns[] = {"*.png",  "*.jpg",  "*.jpeg", "*.webp", "*
                                       "*.tif",  "*.tiff", "*.gif",  "*.ppm",  "*.PNG",
                                       "*.JPG",  "*.JPEG", "*.WEBP"};
 
+// How this program signs the entries it adds to the shared recent list, so
+// Open Recent lists its projects and nothing else.
+const char* const kRecentApp = "effector";
+const std::size_t kRecentCount = 10;
+
 Glib::RefPtr<Gio::ListStore<Gtk::FileFilter>> projectFilters() {
     auto filter = Gtk::FileFilter::create();
     filter->set_name("Effector projects");
@@ -108,6 +114,7 @@ EffectorWindow::EffectorWindow(const Options& initial) {
 EffectorWindow::~EffectorWindow() {
     debounce_.disconnect();
     chainSplitFit_.disconnect();
+    recentChanged_.disconnect();
     loadWindowDelay_.disconnect();
     loadCancel_.store(true, std::memory_order_relaxed);
     if (loader_.joinable()) loader_.join();
@@ -192,6 +199,9 @@ Gtk::Widget& EffectorWindow::buildChainTab() {
     params->append(paramHeading_);
     paramGrid_.set_column_spacing(8);
     paramGrid_.set_row_spacing(6);
+    // A gutter for the overlay scrollbar, which otherwise sits over the spin
+    // buttons' "+" and takes the clicks meant for it.
+    paramGrid_.set_margin_end(14);
     auto* paramScroller = Gtk::make_managed<Gtk::ScrolledWindow>();
     paramScroller->set_policy(Gtk::PolicyType::NEVER, Gtk::PolicyType::AUTOMATIC);
     paramScroller->set_child(paramGrid_);
@@ -1300,6 +1310,12 @@ row.stage-row:selected .stage-action,
 row.stage-row:focus-within .stage-action {
     opacity: 1;
 }
+row.stage-row.drop-before {
+    box-shadow: inset 0 2px @theme_fg_color;
+}
+row.stage-row.drop-after {
+    box-shadow: inset 0 -2px @theme_fg_color;
+}
 )css";
 
 Gtk::Widget& EffectorWindow::buildChainSection() {
@@ -1330,6 +1346,34 @@ Gtk::Widget& EffectorWindow::buildChainSection() {
     chainList_.signal_row_selected().connect(
         [this](Gtk::ListBoxRow*) { onStageSelected(); });
 
+    // A row is dragged by its index (see rebuildChainRows) and dropped between
+    // two rows, which a line along the edge of the row below or above shows.
+    auto drop = Gtk::DropTarget::create(Glib::Value<int>::value_type(), Gdk::DragAction::MOVE);
+    drop->signal_motion().connect(
+        [this](double, double y) {
+            showChainDropSlot(chainDropSlot(y));
+            return Gdk::DragAction::MOVE;
+        },
+        false);
+    drop->signal_leave().connect([this] { showChainDropSlot(-1); });
+    drop->signal_drop().connect(
+        [this](const Glib::ValueBase& value, double, double y) {
+            showChainDropSlot(-1);
+            Glib::Value<int> from;
+            from.init(value.gobj());
+            const int index = from.get();
+            const int slot = chainDropSlot(y);
+            // The slot counts the dragged row itself, which leaves its place
+            // before it takes the new one.
+            const int to = slot > index ? slot - 1 : slot;
+            // Not while the drag is still finishing: the move rebuilds the
+            // rows, the dragged one and its drag source with them.
+            Glib::signal_idle().connect_once([this, index, to] { moveStage(index, to); });
+            return true;
+        },
+        false);
+    chainList_.add_controller(drop);
+
     auto* scroller = Gtk::make_managed<Gtk::ScrolledWindow>();
     scroller->set_policy(Gtk::PolicyType::NEVER, Gtk::PolicyType::AUTOMATIC);
     scroller->set_child(chainList_);
@@ -1409,12 +1453,13 @@ void EffectorWindow::removeStage(int index) {
     requestRender();
 }
 
-void EffectorWindow::moveStage(int index, int delta) {
+void EffectorWindow::moveStage(int from, int to) {
-    const int target = index + delta;
+    const auto count = static_cast<int>(stages_.size());
-    if (index < 0 || static_cast<std::size_t>(index) >= stages_.size()) return;
+    if (from < 0 || from >= count || to < 0 || to >= count || from == to) return;
-    if (target < 0 || static_cast<std::size_t>(target) >= stages_.size()) return;
+    ChainStage stage = std::move(stages_[static_cast<std::size_t>(from)]);
-    std::swap(stages_[static_cast<std::size_t>(index)], stages_[static_cast<std::size_t>(target)]);
+    stages_.erase(stages_.begin() + from);
-    selectedStage_ = target;
+    stages_.insert(stages_.begin() + to, std::move(stage));
+    selectedStage_ = to;
     rebuildChainRows();
     buildParamWidgets();
     requestRender();
@@ -1488,7 +1533,7 @@ void EffectorWindow::rebuildChainRows() {
                 if (delta == 0) {
                     removeStage(index);
                 } else {
-                    moveStage(index, delta);
+                    moveStage(index, index + delta);
                 }
             });
             if (delta == -1) button->set_sensitive(index > 0);
@@ -1497,6 +1542,23 @@ void EffectorWindow::rebuildChainRows() {
         }
 
         row->set_child(*box);
+
+        // The row itself is what is dragged, under the pointer where it was
+        // picked up; a press that goes nowhere is still a click on the row.
+        auto drag = Gtk::DragSource::create();
+        drag->set_actions(Gdk::DragAction::MOVE);
+        drag->signal_prepare().connect(
+            [source = drag.get(), row, index](double x, double y) {
+                source->set_icon(Gtk::WidgetPaintable::create(*row), static_cast<int>(x),
+                               static_cast<int>(y));
+                Glib::Value<int> value;
+                value.init(Glib::Value<int>::value_type());
+                value.set(index);
+                return Gdk::ContentProvider::create(value);
+            },
+            false);
+        row->add_controller(drag);
+
         chainList_.append(*row);
     }
 
@@ -1506,6 +1568,39 @@ void EffectorWindow::rebuildChainRows() {
     scheduleChainSplitFit();
 }
 
+// Where a row dropped at `y` goes: before the row whose upper half `y` is in,
+// or after the last row.
+int EffectorWindow::chainDropSlot(double y) const {
+    for (int i = 0;; ++i) {
+        auto* row = chainList_.get_row_at_index(i);
+        if (row == nullptr) return i;
+        graphene_rect_t bounds;
+        if (!gtk_widget_compute_bounds(GTK_WIDGET(row->gobj()), GTK_WIDGET(chainList_.gobj()),
+                                       &bounds))
+            continue;
+        if (y < bounds.origin.y + bounds.size.height / 2) return i;
+    }
+}
+
+// Marks the edge a drop into `slot` lands on; -1 clears the mark.
+void EffectorWindow::showChainDropSlot(int slot) {
+    const int count = static_cast<int>(stages_.size());
+    for (int i = 0; auto* row = chainList_.get_row_at_index(i); ++i) {
+        const bool before = i == slot;
+        const bool after = slot == count && i == count - 1;
+        if (before) {
+            row->add_css_class("drop-before");
+        } else {
+            row->remove_css_class("drop-before");
+        }
+        if (after) {
+            row->add_css_class("drop-after");
+        } else {
+            row->remove_css_class("drop-after");
+        }
+    }
+}
+
 // 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() {
@@ -1789,16 +1884,37 @@ Gtk::Widget& EffectorWindow::buildMainMenu() {
     add_action("open-project", sigc::mem_fun(*this, &EffectorWindow::onOpenProject));
     add_action("save-project", sigc::mem_fun(*this, &EffectorWindow::onSaveProject));
     add_action("save-project-as", sigc::mem_fun(*this, &EffectorWindow::onSaveProjectAs));
+    // The entry carries the file's URI rather than its path: a target must be
+    // UTF-8, and a file name need not be.
+    add_action_with_parameter("open-recent", Glib::VARIANT_TYPE_STRING,
+                              [this](const Glib::VariantBase& target) {
+                                  const auto uri =
+                                      Glib::VariantBase::cast_dynamic<Glib::Variant<Glib::ustring>>(target).get();
+                                  openProject(Glib::filename_from_uri(uri));
+                              });
+    // Never enabled: it only stands in for an empty list.
+    add_action("no-recent")->set_enabled(false);
+    add_action("show-changelog", sigc::mem_fun(*this, &EffectorWindow::showChangelog));
+    add_action("about", sigc::mem_fun(*this, &EffectorWindow::showAbout));
 
     auto menu = Gio::Menu::create();
     auto open = Gio::Menu::create();
     open->append("New Project", "win.new-project");
     open->append("Open Project…", "win.open-project");
+    recentMenu_ = Gio::Menu::create();
+    open->append_submenu("Open Recent", recentMenu_);
+    rebuildRecentMenu();
+    recentChanged_ = Gtk::RecentManager::get_default()->signal_changed().connect(
+        sigc::mem_fun(*this, &EffectorWindow::rebuildRecentMenu));
     menu->append_section(open);
     auto save = Gio::Menu::create();
     save->append("Save Project", "win.save-project");
     save->append("Save Project As…", "win.save-project-as");
     menu->append_section(save);
+    auto help = Gio::Menu::create();
+    help->append("Changelog", "win.show-changelog");
+    help->append("About Effector", "win.about");
+    menu->append_section(help);
 
     // The shortcuts hang off the window rather than the application, which the
     // window does not belong to yet while it is being built.
@@ -1900,11 +2016,215 @@ void EffectorWindow::onProjectChosen(const Glib::RefPtr<Gio::AsyncResult>& resul
         return;  // cancelled
     }
 
+    openProject(path);
+}
+
+void EffectorWindow::openProject(const std::string& path) {
     try {
         applyProject(loadProject(path), path);
     } catch (const std::exception& error) {
         showError(std::string("Could not open the project: ") + error.what());
+        return;
     }
+    rememberProject(path);
+}
+
+void EffectorWindow::rememberProject(const std::string& path) {
+    Gtk::RecentManager::Data data;
+    data.app_name = kRecentApp;
+    data.app_exec = "effector";
+    data.mime_type = "application/json";
+    try {
+        Gtk::RecentManager::get_default()->add_item(
+            Glib::filename_to_uri(std::filesystem::absolute(path).string()), data);
+    } catch (const Glib::Error&) {
+        // Not a path a URI can name; the project is open all the same.
+    }
+}
+
+void EffectorWindow::rebuildRecentMenu() {
+    std::vector<Glib::RefPtr<Gtk::RecentInfo>> recent;
+    for (const auto& info : Gtk::RecentManager::get_default()->get_items()) {
+        if (info->has_application(kRecentApp) && info->exists()) recent.push_back(info);
+    }
+    std::sort(recent.begin(), recent.end(), [](const auto& a, const auto& b) {
+        return a->get_modified().compare(b->get_modified()) > 0;
+    });
+    if (recent.size() > kRecentCount) recent.resize(kRecentCount);
+
+    // A project is listed by its name, and by its folder too only where two
+    // of the same name would otherwise read alike.
+    std::vector<std::filesystem::path> paths;
+    for (const auto& info : recent) paths.emplace_back(Glib::filename_from_uri(info->get_uri()));
+    recentMenu_->remove_all();
+    for (std::size_t i = 0; i < recent.size(); ++i) {
+        std::string label = paths[i].stem().string();
+        const auto sameName = std::count_if(paths.begin(), paths.end(), [&](const auto& other) {
+            return other.stem() == paths[i].stem();
+        });
+        if (sameName > 1) label += " (" + paths[i].parent_path().filename().string() + ")";
+        // The menu reads an underscore as a mnemonic.
+        const std::string display = Glib::filename_display_name(label);
+        std::string escaped;
+        for (const char c : display) {
+            escaped += c;
+            if (c == '_') escaped += '_';
+        }
+        auto item = Gio::MenuItem::create(escaped, "");
+        item->set_action_and_target("win.open-recent",
+                                    Glib::Variant<Glib::ustring>::create(recent[i]->get_uri()));
+        recentMenu_->append_item(item);
+    }
+    if (recent.empty()) recentMenu_->append("No Recent Projects", "win.no-recent");
+}
+
+// ------------------------------------------------------------ changelog ---
+
+namespace {
+
+// Lays CHANGELOG.md out in a text buffer. It reads only the little Markdown
+// the file uses -- headings, bullets wrapped onto indented lines, and `code`
+// -- which is all a changelog needs.
+void fillChangelog(const Glib::RefPtr<Gtk::TextBuffer>& buffer, std::string_view markdown) {
+    auto tags = buffer->get_tag_table();
+    auto tag = [&](const char* name, auto&& configure) {
+        auto made = Gtk::TextTag::create(name);
+        configure(*made);
+        tags->add(made);
+    };
+    tag("title", [](Gtk::TextTag& t) {
+        t.property_weight() = Pango::Weight::BOLD;
+        t.property_scale() = 1.6;
+        t.property_pixels_below_lines() = 6;
+    });
+    tag("release", [](Gtk::TextTag& t) {
+        t.property_weight() = Pango::Weight::BOLD;
+        t.property_scale() = 1.3;
+        t.property_pixels_above_lines() = 18;
+        t.property_pixels_below_lines() = 2;
+    });
+    tag("section", [](Gtk::TextTag& t) {
+        t.property_weight() = Pango::Weight::BOLD;
+        t.property_pixels_above_lines() = 8;
+        t.property_pixels_below_lines() = 2;
+    });
+    tag("item", [](Gtk::TextTag& t) {
+        t.property_left_margin() = 28;
+        t.property_indent() = -14;
+        t.property_pixels_below_lines() = 3;
+    });
+    tag("para", [](Gtk::TextTag& t) { t.property_pixels_below_lines() = 6; });
+    tag("code", [](Gtk::TextTag& t) { t.property_family() = "monospace"; });
+
+    // Gather each block -- a heading, a bullet, a paragraph -- whole first,
+    // since a bullet or a paragraph goes on over several lines.
+    struct Block {
+        std::string kind;
+        std::string text;
+    };
+    std::vector<Block> blocks;
+    bool open = false;  // the last block still takes continuation lines
+    std::size_t pos = 0;
+    while (pos <= markdown.size()) {
+        auto end = markdown.find('\n', pos);
+        if (end == std::string_view::npos) end = markdown.size();
+        std::string line(markdown.substr(pos, end - pos));
+        pos = end + 1;
+
+        const auto first = line.find_first_not_of(' ');
+        if (first == std::string::npos) {
+            open = false;
+        } else if (line.rfind("# ", 0) == 0) {
+            blocks.push_back({"title", line.substr(2)});
+            open = false;
+        } else if (line.rfind("## ", 0) == 0) {
+            // "[0.5.0] - 2026-09-26" reads as "0.5.0 — 2026-09-26".
+            std::string text = line.substr(3);
+            std::erase(text, '[');
+            std::erase(text, ']');
+            if (const auto dash = text.find(" - "); dash != std::string::npos) {
+                text.replace(dash, 3, " — ");
+            }
+            blocks.push_back({"release", text});
+            open = false;
+        } else if (line.rfind("### ", 0) == 0) {
+            blocks.push_back({"section", line.substr(4)});
+            open = false;
+        } else if (line.rfind("- ", 0) == 0) {
+            blocks.push_back({"item", "•  " + line.substr(2)});
+            open = true;
+        } else if (open) {
+            blocks.back().text += " " + line.substr(first);
+        } else {
+            blocks.push_back({"para", line.substr(first)});
+            open = true;
+        }
+    }
+
+    auto at = buffer->end();
+    for (std::size_t i = 0; i < blocks.size(); ++i) {
+        const auto& block = blocks[i];
+        // Split on the backticks: every odd piece is code.
+        std::size_t start = 0;
+        bool code = false;
+        while (start <= block.text.size()) {
+            auto tick = block.text.find('`', start);
+            if (tick == std::string::npos) tick = block.text.size();
+            if (tick > start) {
+                std::vector<Glib::ustring> names{block.kind};
+                if (code) names.emplace_back("code");
+                at = buffer->insert_with_tags_by_name(at, block.text.substr(start, tick - start), names);
+            }
+            start = tick + 1;
+            code = !code;
+        }
+        if (i + 1 < blocks.size()) at = buffer->insert_with_tag(at, "\n", block.kind);
+    }
+}
+
+}  // namespace
+
+void EffectorWindow::showChangelog() {
+    if (!changelogWindow_) {
+        changelogWindow_ = std::make_unique<Gtk::Window>();
+        changelogWindow_->set_title("Changelog");
+        changelogWindow_->set_transient_for(*this);
+        changelogWindow_->set_default_size(560, 640);
+        changelogWindow_->set_hide_on_close(true);
+
+        auto* text = Gtk::make_managed<Gtk::TextView>();
+        text->set_name("changelog");
+        text->set_editable(false);
+        text->set_cursor_visible(false);
+        text->set_wrap_mode(Gtk::WrapMode::WORD);
+        text->set_left_margin(18);
+        text->set_right_margin(18);
+        text->set_top_margin(12);
+        text->set_bottom_margin(18);
+        fillChangelog(text->get_buffer(), kChangelog);
+
+        auto* scroller = Gtk::make_managed<Gtk::ScrolledWindow>();
+        scroller->set_policy(Gtk::PolicyType::NEVER, Gtk::PolicyType::AUTOMATIC);
+        scroller->set_child(*text);
+        changelogWindow_->set_child(*scroller);
+    }
+    changelogWindow_->present();
+}
+
+void EffectorWindow::showAbout() {
+    if (!aboutDialog_) {
+        aboutDialog_ = std::make_unique<Gtk::AboutDialog>();
+        aboutDialog_->set_transient_for(*this);
+        aboutDialog_->set_modal(true);
+        aboutDialog_->set_hide_on_close(true);
+        aboutDialog_->set_program_name("Effector");
+        aboutDialog_->set_version(std::string(kVersion));
+        aboutDialog_->set_comments("Image effects, cascaded through a chain.");
+        aboutDialog_->set_logo_icon_name("applications-graphics");
+        aboutDialog_->set_copyright("Copyright © 2026 Si");
+        aboutDialog_->set_license_type(Gtk::License::GPL_3_0);
+    }
+    aboutDialog_->present();
 }
 
 void EffectorWindow::onSaveProject() {
@@ -1951,6 +2271,7 @@ void EffectorWindow::writeProject(const std::string& path) {
     clearError();
     projectPath_ = path;
     updateTitle();
+    rememberProject(path);
     status_.set_text("Saved " + path);
     status_.set_tooltip_text("Saved " + path);
 }

src/gui/window.hpp

@@ -91,7 +91,11 @@ private:
     Gtk::Widget& buildAddMenu();      // the menu of effects that can be appended
     void appendStage(const EffectPtr& effect);
     void removeStage(int index);
-    void moveStage(int index, int delta);
+    void moveStage(int from, int to);  // `to` is the index it ends up at
+    // Dragging a row: the slot between rows it would drop into, and the line
+    // that shows it.
+    int chainDropSlot(double y) const;
+    void showChainDropSlot(int slot);
     // The check on a chain row: the stage stays where it is, and is skipped.
     void setStageEnabled(int index, bool enabled);
     void rebuildChainRows();
@@ -104,11 +108,18 @@ private:
     void selectStage(int index);
     void onStageSelected();
     Gtk::Widget& buildMainMenu();     // the header menu: new, open, save project
+    void showChangelog();
+    void showAbout();
     Project currentProject() const;
     void applyProject(const Project& project, const std::string& path);
     void clearSources();
     void onNewProject();
     void onOpenProject();
+    void openProject(const std::string& path);
+    // Open Recent: the projects this program opened or saved, newest first,
+    // kept in the desktop's shared list of recently used files.
+    void rememberProject(const std::string& path);
+    void rebuildRecentMenu();
     void onProjectChosen(const Glib::RefPtr<Gio::AsyncResult>& result,
                          const Glib::RefPtr<Gtk::FileDialog>& dialog);
     void onSaveProject();       // falls back to Save As while the project is untitled
@@ -163,6 +174,8 @@ private:
     Image result_;
     std::uint64_t seed_ = 0;
     std::string projectPath_;  // empty until the project has been saved once
+    Glib::RefPtr<Gio::Menu> recentMenu_;
+    sigc::connection recentChanged_;  // the recent list outlives the window
     bool suspendRender_ = true;
 
     // Source loading. Decoding a batch of large photographs takes seconds, so
@@ -198,6 +211,9 @@ private:
     Gtk::Button* addButton_ = nullptr;
     // Built fresh with the progress window, and null whenever it is closed.
     std::unique_ptr<Gtk::Window> loadWindow_;
+    // Opened from the menu on first use, then shown again rather than rebuilt.
+    std::unique_ptr<Gtk::Window> changelogWindow_;
+    std::unique_ptr<Gtk::AboutDialog> aboutDialog_;
     Gtk::ProgressBar* loadBar_ = nullptr;
     Gtk::Label* loadFileLabel_ = nullptr;
     Gtk::Box sourcesSection_;  // hidden while the chain needs no sources

src/main.cpp

@@ -13,6 +13,7 @@
 #include "core/image.hpp"
 #include "core/registry.hpp"
 #include "core/rng.hpp"
+#include "core/version.hpp"
 #include "gui/app.hpp"
 
 namespace {
@@ -78,6 +79,10 @@ int main(int argc, char** argv) {
             std::cout << effector::usage(argv[0]);
             return 0;
         }
+        if (options.showVersion) {
+            std::cout << "effector " << effector::kVersion << "\n";
+            return 0;
+        }
         if (options.listEffects) {
             for (const auto& effect : effector::effects()) {
                 std::cout << effect->name() << "\t" << effect->title() << " - "

tests/CMakeLists.txt

@@ -3,6 +3,8 @@
 add_executable(effector_tests core_tests.cpp ../src/cli/options.cpp)
 target_link_libraries(effector_tests PRIVATE effector_core)
 target_compile_options(effector_tests PRIVATE -Wall -Wextra -Wpedantic)
+# The version test reads the Arch PKGBUILD to keep its pkgver in step.
+target_compile_definitions(effector_tests PRIVATE EFFECTOR_SOURCE_DIR="${PROJECT_SOURCE_DIR}")
 
 add_test(NAME core COMMAND effector_tests)
 

tests/core_tests.cpp

@@ -24,6 +24,7 @@
 #include "core/registry.hpp"
 #include "core/rng.hpp"
 #include "core/style.hpp"
+#include "core/version.hpp"
 #include "effects/blur.hpp"
 #include "effects/grain.hpp"
 #include "effects/monochrome.hpp"
@@ -638,6 +639,49 @@ int main() {
                         solid(100, 100, 0, 0, 255)),
               "zero opacity leaves the input untouched");
 
+        // Halo: none by default, a shadow moved by its offset, a glow all round.
+        check(sameBytes(renderOverlay(blue, 100, 100, at),
+                        renderOverlay(blue, 100, 100, [&] {
+                            ParamValues none = at;
+                            none["overlay_halo"] = std::string("none");
+                            return none;
+                        }())),
+              "no halo is the default");
+        ParamValues shadowed = at;
+        shadowed["overlay_halo"] = std::string("shadow");
+        shadowed["overlay_halo_size"] = 0L;
+        shadowed["overlay_halo_opacity"] = 1.0;
+        shadowed["overlay_shadow_x"] = 5L;
+        shadowed["overlay_shadow_y"] = 5L;
+        const auto shadow = renderOverlay(blue, 100, 100, shadowed);
+        const auto dark = pixel(shadow, 72, 62);  // past the logo's bottom right corner (70, 60)
+        check(dark[0] == 0 && dark[1] == 0 && dark[2] == 0,
+              "a hard shadow is cast down and right by its offset");
+        check(isBlue(pixel(shadow, 28, 50)) && isRed(pixel(shadow, 50, 50)),
+              "it leaves the other side alone and stays beneath the image");
+        shadowed["overlay_halo_size"] = 12L;
+        const auto soft = pixel(renderOverlay(blue, 100, 100, shadowed), 78, 50);
+        check(soft[2] > 0 && soft[2] < 255, "a soft shadow fades out past the edge");
+
+        ParamValues glowing = at;
+        glowing["overlay_halo"] = std::string("glow");
+        const auto glow = renderOverlay(blue, 100, 100, glowing);
+        const auto left = pixel(glow, 27, 50);
+        const auto right = pixel(glow, 72, 50);
+        check(left[0] > 0 && left[0] == right[0] && left[1] == right[1],
+              "a glow lightens both sides alike");
+        check(isBlue(pixel(glow, 2, 2)), "and fades out before the far corners");
+        glowing["overlay_halo_spread"] = 0.5;
+        check(pixel(renderOverlay(blue, 100, 100, glowing), 27, 50)[0] > left[0],
+              "spread strengthens the halo near the edge");
+
+        ParamValues offCanvas = shadowed;
+        offCanvas["overlay_halo_size"] = 0L;
+        offCanvas["overlay_offset_x"] = -70L;  // the logo ends just left of the canvas
+        offCanvas["overlay_shadow_x"] = 20L;
+        const auto cast = pixel(renderOverlay(blue, 100, 100, offCanvas), 5, 50);
+        check(cast[2] == 0, "an image off the canvas still casts its shadow onto it");
+
         // No image chosen is the state the interface starts in: a pass through.
         check(sameBytes(renderOverlay(blue, 100, 100, {}), solid(100, 100, 0, 0, 255)),
               "with no image chosen the stage passes its input through");
@@ -1672,6 +1716,28 @@ int main() {
         std::filesystem::remove_all(dir);
     }
 
+    std::cout << "version\n";
+    {
+        // A release is the version in CMakeLists.txt and its entry at the top
+        // of CHANGELOG.md; bumping one without the other fails here.
+        const std::string_view log = kChangelog;
+        const auto newest = log.find("\n## [");
+        check(newest != std::string_view::npos &&
+                  log.substr(newest + 5).starts_with(std::string(kVersion) + "]"),
+              "the newest changelog entry is this version");
+        std::ifstream pkgbuild(std::string(EFFECTOR_SOURCE_DIR) + "/packaging/arch/PKGBUILD");
+        std::string line;
+        std::string pkgver;
+        while (std::getline(pkgbuild, line)) {
+            if (line.starts_with("pkgver=")) pkgver = line.substr(7);
+        }
+        check(pkgver == kVersion, "the Arch PKGBUILD packages this version");
+        const auto options = parsedOptions({"--version"});
+        check(options && options->showVersion, "--version is understood");
+        const auto shortOptions = parsedOptions({"-V"});
+        check(shortOptions && shortOptions->showVersion, "and so is -V");
+    }
+
     std::cout << (failures == 0 ? "\nall checks passed\n" : "\n" + std::to_string(failures) + " failed\n");
     return failures == 0 ? 0 : 1;
 }

tests/gui_tests.cpp

@@ -6,6 +6,7 @@
 
 #include <chrono>
 #include <cstdlib>
+#include <filesystem>
 #include <iostream>
 #include <memory>
 #include <string>
@@ -13,7 +14,9 @@
 #include <vector>
 
 #include "cli/options.hpp"
+#include "core/project.hpp"
 #include "core/registry.hpp"
+#include "core/version.hpp"
 #include "gui/window.hpp"
 
 namespace {
@@ -122,6 +125,30 @@ bool addFromMenu(Gtk::MenuButton& add, const std::string& title) {
     return true;
 }
 
+// The drop target the chain list reorders its rows with.
+GtkDropTarget* chainDropTarget(Gtk::Widget& list) {
+    GListModel* controllers = gtk_widget_observe_controllers(list.gobj());
+    GtkDropTarget* found = nullptr;
+    for (guint i = 0; i < g_list_model_get_n_items(controllers) && found == nullptr; ++i) {
+        auto* controller = g_list_model_get_item(controllers, i);
+        if (GTK_IS_DROP_TARGET(controller)) found = GTK_DROP_TARGET(controller);
+        g_object_unref(controller);
+    }
+    g_object_unref(controllers);
+    return found;
+}
+
+// What dropping the row of stage `index` at `y` does; a real drag needs a
+// pointer, which the tests do not have.
+void dropStage(GtkDropTarget* drop, int index, double y) {
+    GValue value = G_VALUE_INIT;
+    g_value_init(&value, G_TYPE_INT);
+    g_value_set_int(&value, index);
+    gboolean handled = FALSE;
+    g_signal_emit_by_name(drop, "drop", &value, 1.0, y, &handled);
+    g_value_unset(&value);
+}
+
 void runTests(Gtk::Window& window) {
     const auto& effects = effector::effects();
 
@@ -239,6 +266,43 @@ void runTests(Gtk::Window& window) {
           "Remove drops the stage and renumbers the rest");
     check(!sources->get_visible(), "and the sources hide again");
 
+    std::cout << "drag and drop\n";
+    addFromMenu(*add, "Scanlines");
+    for (const auto& effect : effects) {
+        if (effect->title() != "Blur" && effect->title() != "Scanlines") {
+            addFromMenu(*add, effect->title());
+            break;
+        }
+    }
+    GtkDropTarget* drop = chainDropTarget(*chainList);
+    check(drop != nullptr, "the chain list takes drops");
+    if (drop != nullptr && rowCount(*chainList) == 3) {
+        const std::string first = rowTitle(*chainList, 0).substr(3);
+        const std::string second = rowTitle(*chainList, 1).substr(3);
+        const std::string third = rowTitle(*chainList, 2).substr(3);
+        const double bottom = chainList->get_row_at_index(2)->get_height() * 3.0;
+        GdkDragAction action = GDK_ACTION_NONE;
+        g_signal_emit_by_name(drop, "motion", 1.0, bottom, &action);
+        check(chainList->get_row_at_index(2)->has_css_class("drop-after"),
+              "dragging past the last row marks its bottom edge");
+        dropStage(drop, 0, bottom);
+        pump();
+        check(rowTitle(*chainList, 0) == "1. " + second && rowTitle(*chainList, 1) == "2. " + third &&
+                  rowTitle(*chainList, 2) == "3. " + first,
+              "dropping the first stage past the last moves it to the end");
+        check(chainList->get_selected_row() == chainList->get_row_at_index(2),
+              "and selects it");
+        check(!chainList->get_row_at_index(2)->has_css_class("drop-after"),
+              "and clears the mark");
+        dropStage(drop, 2, 1.0);
+        pump();
+        check(rowTitle(*chainList, 0) == "1. " + first && rowTitle(*chainList, 1) == "2. " + second,
+              "dropping on the top edge of the first row moves it to the front");
+    }
+    for (int i = rowCount(*chainList) - 1; i > 0; --i) {
+        if (auto* removeRow = withTooltip(*chainList->get_row_at_index(i), "Remove")) press(*removeRow);
+    }
+
     std::cout << "many stages\n";
     for (int i = 0; i < 4; ++i) addFromMenu(*add, effects[static_cast<std::size_t>(i) % effects.size()]->title());
     pump();
@@ -271,6 +335,111 @@ void runTests(Gtk::Window& window) {
     pump();
 }
 
+// The labels of the entries under the "Open Recent" submenu of `model`, or
+// nothing when there is no such submenu.
+void recentLabels(GMenuModel* model, std::vector<std::string>& out, bool& found) {
+    for (int i = 0; i < g_menu_model_get_n_items(model); ++i) {
+        char* label = nullptr;
+        g_menu_model_get_item_attribute(model, i, G_MENU_ATTRIBUTE_LABEL, "s", &label);
+        const std::string text = label != nullptr ? label : "";
+        g_free(label);
+        if (GMenuModel* section = g_menu_model_get_item_link(model, i, G_MENU_LINK_SECTION)) {
+            recentLabels(section, out, found);
+            g_object_unref(section);
+        }
+        if (GMenuModel* submenu = g_menu_model_get_item_link(model, i, G_MENU_LINK_SUBMENU)) {
+            if (text == "Open Recent") {
+                found = true;
+                for (int j = 0; j < g_menu_model_get_n_items(submenu); ++j) {
+                    char* entry = nullptr;
+                    g_menu_model_get_item_attribute(submenu, j, G_MENU_ATTRIBUTE_LABEL, "s", &entry);
+                    out.emplace_back(entry != nullptr ? entry : "");
+                    g_free(entry);
+                }
+            }
+            g_object_unref(submenu);
+        }
+    }
+}
+
+std::vector<std::string> recentEntries(Gtk::Window& window) {
+    std::vector<Gtk::MenuButton*> buttons;
+    collect<Gtk::MenuButton>(window, [](Gtk::MenuButton& b) { return b.get_tooltip_text() == "Project menu"; },
+                             buttons);
+    std::vector<std::string> labels;
+    bool found = false;
+    if (buttons.empty()) return labels;
+    auto* popover = dynamic_cast<Gtk::PopoverMenu*>(buttons.front()->get_popover());
+    if (popover == nullptr || !popover->get_menu_model()) return labels;
+    recentLabels(popover->get_menu_model()->gobj(), labels, found);
+    if (!found) labels.emplace_back("<no Open Recent submenu>");
+    return labels;
+}
+
+// The version and the changelog, each a menu entry away.
+void testHelpWindows(Gtk::Window& window) {
+    std::cout << "changelog and about\n";
+    auto toplevel = [](const std::string& title) -> Gtk::Window* {
+        for (auto* w : Gtk::Window::list_toplevels()) {
+            if (w->get_title() == title && w->get_visible()) return w;
+        }
+        return nullptr;
+    };
+
+    window.activate_action("win.show-changelog");
+    pump(200);
+    auto* changelog = toplevel("Changelog");
+    check(changelog != nullptr, "Changelog opens a window");
+    auto* text = changelog != nullptr ? named<Gtk::TextView>(*changelog, "changelog") : nullptr;
+    const std::string shown = text != nullptr ? std::string(text->get_buffer()->get_text()) : "";
+    check(shown.find(std::string(effector::kVersion) + " — ") != std::string::npos,
+          "listing this version as a release");
+    check(shown.find("[") == std::string::npos && shown.find("`") == std::string::npos &&
+              shown.find("### ") == std::string::npos,
+          "with the Markdown laid out rather than shown");
+    if (changelog != nullptr) changelog->close();
+    pump(50);
+    check(toplevel("Changelog") == nullptr, "and closes");
+
+    window.activate_action("win.about");
+    pump(200);
+    Gtk::AboutDialog* about = nullptr;
+    for (auto* w : Gtk::Window::list_toplevels()) {
+        if (auto* dialog = dynamic_cast<Gtk::AboutDialog*>(w); dialog != nullptr && dialog->get_visible()) {
+            about = dialog;
+        }
+    }
+    check(about != nullptr && about->get_version() == std::string(effector::kVersion),
+          "About Effector shows the version");
+    if (about != nullptr) about->close();
+    pump(50);
+}
+
+void testRecentProjects(Gtk::Window& window, const std::filesystem::path& dir) {
+    std::cout << "recent projects\n";
+    check(recentEntries(window) == std::vector<std::string>{"No Recent Projects"},
+          "Open Recent starts out empty");
+
+    // Two projects of the same name in different folders, and a third.
+    std::filesystem::create_directories(dir / "first");
+    std::filesystem::create_directories(dir / "second");
+    const std::filesystem::path paths[] = {dir / "first" / "my_look.json", dir / "second" / "my_look.json",
+                                           dir / "other.json"};
+    effector::Project project;
+    project.stages.push_back({effector::effectByName("blur"), {}});  // renders with no sources
+    for (const auto& path : paths) {
+        effector::saveProject(path.string(), project);
+        window.activate_action("win.open-recent",
+                               Glib::Variant<Glib::ustring>::create(Glib::filename_to_uri(path.string())));
+        pump(50);
+    }
+    pump(500);  // the recent list is written, and announced, from an idle
+    check(window.get_title() == "other — Effector", "an entry opens its project");
+    const auto labels = recentEntries(window);
+    check(labels == std::vector<std::string>{"other", "my__look (second)", "my__look (first)"},
+          "opened projects are listed newest first, a shared name with its folder");
+}
+
 }  // namespace
 
 int main(int argc, char** argv) {
@@ -283,17 +452,25 @@ int main(int argc, char** argv) {
         return 77;
     }
 
+    // Keep the projects the tests open out of the user's own recent list.
+    std::string dataTemplate = (std::filesystem::temp_directory_path() / "effector-gui-XXXXXX").string();
+    const std::filesystem::path dataDir = g_mkdtemp(dataTemplate.data());
+    g_setenv("XDG_DATA_HOME", dataDir.c_str(), TRUE);
+
     auto app = Gtk::Application::create("org.effector.GuiTests",
                                         Gio::Application::Flags::NON_UNIQUE);
-    app->signal_activate().connect([&app] {
+    app->signal_activate().connect([&app, &dataDir] {
         auto window = std::make_unique<effector::EffectorWindow>(effector::Options{});
         app->add_window(*window);
         window->present();
         pump(300);
         runTests(*window);
+        testHelpWindows(*window);
+        testRecentProjects(*window, dataDir / "projects");
         app->remove_window(*window);
     });
     const int status = app->run(argc > 0 ? 1 : 0, argv);
+    std::filesystem::remove_all(dataDir);
     if (status != 0) return status;
     std::cout << (failures == 0 ? "all passed\n" : std::to_string(failures) + " failed\n");
     return failures;