Show Tile swap's Swap rate as a slider, and let it go slower

A new ParamSpec::slider() marks an Int or Double param to be shown in
the interface as a Gtk::Scale with its minimum and maximum marked under
the ends, rather than a spin button; the command line and the project
file are unchanged. Swap rate uses it, and now runs from 0 to 5 in
steps of 0.01 (was 0 to 30 in steps of 0.1): with every tile swapping
on its own, even 0.1 swapped the canvas many times a second.

Version 0.8.2.

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

CHANGELOG.md

@@ -4,6 +4,13 @@ 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.
 
+## [0.8.2] - 2026-09-30
+
+### Changed
+- The Swap rate of Tile swap is a slider marked with its range, and goes
+  down in steps of 0.01 rather than 0.1, so a clip can swap its tiles much
+  more slowly. Its top end is now 5 swaps a second (it was 30).
+
 ## [0.8.1] - 2026-09-26
 
 ### Added

CLAUDE.md

@@ -80,6 +80,10 @@ travel as `ParamValues` (a
 `map<string, variant<long,double,bool,string>>`), read back with
 `paramInt`/`paramDouble`/`paramBool`/`paramChoice`.
 
+An Int or Double param marked `.slider()` is shown in
+the interface as a slider with its minimum and maximum marked instead of a spin
+button; nothing else changes.
+
 A param can also be marked `.styled()`, which says a *named style* carries it
 rather than the stage it sits on: the font and the colour of a text stage, but
 never its words or its placement. The pool a style comes from is named by

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.20)
-project(effector VERSION 0.8.1 LANGUAGES CXX)
+project(effector VERSION 0.8.2 LANGUAGES CXX)
 
 set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)

packaging/arch/PKGBUILD

@@ -2,7 +2,7 @@
 # so pkgver must follow the project() line of CMakeLists.txt (the version core
 # test checks it). From this folder: makepkg -si
 pkgname=effector
-pkgver=0.8.1
+pkgver=0.8.2
 pkgrel=1
 pkgdesc='Image effects app: a GTK4 interface and a headless CLI over pluggable effects'
 arch=('x86_64' 'aarch64')

src/core/params.cpp

@@ -16,6 +16,12 @@ ParamSpec ParamSpec::styled() const {
     return copy;
 }
 
+ParamSpec ParamSpec::slider() const {
+    ParamSpec copy = *this;
+    copy.onSlider = true;
+    return copy;
+}
+
 ParamSpec ParamSpec::makeInt(std::string key, std::string label, long defaultValue, long minimum,
                              long maximum, std::string help, long step) {
     ParamSpec spec;

src/core/params.hpp

@@ -27,6 +27,9 @@ struct ParamSpec {
     // Whether a named style carries this param rather than the stage it sits
     // on: see core/style.hpp.
     bool inStyle = false;
+    // Whether the interface shows this number as a slider marked with its
+    // range rather than as a spin button: see slider().
+    bool onSlider = false;
 
     std::string flag() const;  // "strip_height" -> "--strip-height"
 
@@ -35,6 +38,11 @@ struct ParamSpec {
     // signatures they have.
     ParamSpec styled() const;
 
+    // A copy of this Int or Double spec shown as a slider in the interface, for
+    // a number whose place between its minimum and maximum says more than its
+    // digits do. The command line and the project file are unchanged.
+    ParamSpec slider() const;
+
     static ParamSpec makeInt(std::string key, std::string label, long defaultValue, long minimum,
                              long maximum, std::string help = {}, long step = 1);
     static ParamSpec makeDouble(std::string key, std::string label, double defaultValue,

src/effects/tileswap.cpp

@@ -25,10 +25,11 @@ const std::vector<ParamSpec>& TileSwapEffect::params() const {
                            "How many tiles are dropped on the canvas; scattered layout only."),
         ParamSpec::makeBool("tileswap_keep_order", "Cycle images in order", false,
                             "Take tiles from the images in order instead of picking randomly."),
-        ParamSpec::makeDouble("tileswap_rate", "Swap rate", 1.0, 0.0, 30.0,
+        ParamSpec::makeDouble("tileswap_rate", "Swap rate", 1.0, 0.0, 5.0,
                               "Swaps per second of each tile, rounded so that the clip loops "
                               "without a jump; 0 for none.",
-                              0.1, 1),
+                              0.01, 2)
+            .slider(),
     };
     return specs;
 }

src/gui/window.cpp

@@ -5,6 +5,7 @@
 #include <cmath>
 #include <cstdint>
 #include <filesystem>
+#include <iomanip>
 #include <sstream>
 #include <utility>
 
@@ -74,14 +75,14 @@ Gtk::Label* sectionLabel(const char* text) {
     return label;
 }
 
-// A GtkSpinButton takes every wheel turn over it: it grabs the focus and
-// spins its value, so scrolling down a column of params stops dead at the
-// first spin under the pointer and quietly changes it. This hands the wheel to
+// A GtkSpinButton (or a GtkScale) takes every wheel turn over it: it grabs the
+// focus and spins its value, so scrolling down a column of params stops dead at
+// the first spin under the pointer and quietly changes it. This hands the wheel to
 // the view instead unless the spin already has the focus -- the user clicked
 // into it and means to adjust it. It runs in the capture phase, ahead of the
 // spin's own controller, and so has to scroll the enclosing ScrolledWindow
 // itself: stopping the event there stops it for the window as well.
-void scrollPastUnlessFocused(Gtk::SpinButton& spin) {
+void scrollPastUnlessFocused(Gtk::Widget& spin) {
     auto scroll = Gtk::EventControllerScroll::create();
     scroll->set_propagation_phase(Gtk::PropagationPhase::CAPTURE);
     scroll->set_flags(Gtk::EventControllerScroll::Flags::VERTICAL);
@@ -950,14 +951,39 @@ void EffectorWindow::buildParamWidgets() {
             }
             case ParamSpec::Type::Int:
             case ParamSpec::Type::Double: {
+                const double value =
+                    spec.type == ParamSpec::Type::Int
+                        ? static_cast<double>(
+                              paramInt(values, spec.key, static_cast<long>(spec.defaultValue)))
+                        : paramDouble(values, spec.key, spec.defaultValue);
+                if (spec.onSlider) {
+                    // The ends are marked with their values, so where the
+                    // number sits in its range can be read at a glance.
+                    const int digits = spec.type == ParamSpec::Type::Int ? 0 : spec.digits;
+                    auto scale = std::make_unique<Gtk::Scale>(Gtk::Orientation::HORIZONTAL);
+                    scale->set_range(spec.minimum, spec.maximum);
+                    scale->set_increments(spec.step, spec.step * 10);
+                    scale->set_round_digits(digits);
+                    scale->set_digits(digits);
+                    scale->set_draw_value(true);
+                    scale->set_value_pos(Gtk::PositionType::RIGHT);
+                    const auto mark = [digits](double at) {
+                        return Glib::ustring::format(std::fixed, std::setprecision(digits), at);
+                    };
+                    scale->add_mark(spec.minimum, Gtk::PositionType::BOTTOM, mark(spec.minimum));
+                    scale->add_mark(spec.maximum, Gtk::PositionType::BOTTOM, mark(spec.maximum));
+                    scale->set_value(value);
+                    scale->signal_value_changed().connect(
+                        sigc::mem_fun(*this, &EffectorWindow::onParamChanged));
+                    scrollPastUnlessFocused(*scale);
+                    widget = std::move(scale);
+                    break;
+                }
                 auto spin = std::make_unique<Gtk::SpinButton>();
                 spin->set_range(spec.minimum, spec.maximum);
                 spin->set_increments(spec.step, spec.step * 10);
                 spin->set_digits(spec.type == ParamSpec::Type::Int ? 0 : spec.digits);
-                spin->set_value(spec.type == ParamSpec::Type::Int
-                                    ? static_cast<double>(paramInt(values, spec.key,
-                                                                  static_cast<long>(spec.defaultValue)))
-                                    : paramDouble(values, spec.key, spec.defaultValue));
+                spin->set_value(value);
                 spin->signal_value_changed().connect(
                     sigc::mem_fun(*this, &EffectorWindow::onParamChanged));
                 scrollPastUnlessFocused(*spin);
@@ -1065,12 +1091,17 @@ ParamValues EffectorWindow::paramValues() const {
                 values[entry.spec.key] = static_cast<Gtk::Switch*>(entry.widget)->get_active();
                 break;
             case ParamSpec::Type::Int:
-                values[entry.spec.key] =
-                    static_cast<long>(static_cast<Gtk::SpinButton*>(entry.widget)->get_value());
-                break;
-            case ParamSpec::Type::Double:
-                values[entry.spec.key] = static_cast<Gtk::SpinButton*>(entry.widget)->get_value();
+            case ParamSpec::Type::Double: {
+                const double value =
+                    entry.spec.onSlider ? static_cast<Gtk::Scale*>(entry.widget)->get_value()
+                                        : static_cast<Gtk::SpinButton*>(entry.widget)->get_value();
+                if (entry.spec.type == ParamSpec::Type::Int) {
+                    values[entry.spec.key] = std::lround(value);
+                } else {
+                    values[entry.spec.key] = value;
+                }
                 break;
+            }
             case ParamSpec::Type::Path:
             case ParamSpec::Type::Text:
                 values[entry.spec.key] =

tests/gui_tests.cpp

@@ -7,6 +7,7 @@
 #include <chrono>
 #include <cstdlib>
 #include <filesystem>
+#include <iomanip>
 #include <iostream>
 #include <memory>
 #include <string>
@@ -633,6 +634,50 @@ void testFont(Gtk::Window& window, const std::filesystem::path& dir) {
           "a family chosen there is saved with the project");
 }
 
+void testSlider(Gtk::Window& window, const std::filesystem::path& dir) {
+    std::cout << "slider\n";
+    std::filesystem::create_directories(dir);
+    const auto path = dir / "swapping.json";
+    effector::Project project;
+    project.video.enabled = true;
+    effector::ChainStage stage{effector::effectByName("tileswap"), {}};
+    stage.values["tileswap_rate"] = 0.5;
+    project.stages.push_back(stage);
+    effector::saveProject(path.string(), project);
+    window.activate_action("win.open-recent",
+                           Glib::Variant<Glib::ustring>::create(Glib::filename_to_uri(path.string())));
+    pump(300);
+
+    auto* chainList = named<Gtk::ListBox>(window, "chain-list");
+    if (chainList != nullptr && chainList->get_row_at_index(0) != nullptr) {
+        chainList->select_row(*chainList->get_row_at_index(0));
+    }
+    pump(100);
+    std::vector<Gtk::Scale*> scales;
+    collect<Gtk::Scale>(window, [](Gtk::Scale& s) { return s.is_drawable(); }, scales);
+    check(scales.size() == 1, "a param marked as a slider is shown as one");
+    if (scales.size() != 1) return;
+    auto* scale = scales.front();
+    auto adjustment = scale->get_adjustment();
+    // Written the way the locale writes numbers, as the interface does.
+    const auto mark = [](double at) {
+        return std::string(Glib::ustring::format(std::fixed, std::setprecision(2), at));
+    };
+    check(adjustment->get_lower() == 0.0 && adjustment->get_upper() == 5.0 &&
+              showsText(*scale, mark(0.0)) && showsText(*scale, mark(5.0)),
+          "with its range marked at both ends");
+    check(scale->get_value() == 0.5, "and shows the value saved");
+
+    scale->set_value(0.05);
+    pump(100);
+    window.activate_action("win.save-project");
+    pump(100);
+    const auto saved = effector::loadProject(path.string());
+    check(saved.stages.size() == 1 &&
+              std::abs(effector::paramDouble(saved.stages[0].values, "tileswap_rate", 0.0) - 0.05) < 1e-9,
+          "a value slid to is saved with the project");
+}
+
 bool actionEnabled(Gtk::Window& window, const std::string& name) {
     auto action = dynamic_cast<Gtk::ApplicationWindow&>(window).lookup_action(name);
     return action && action->get_enabled();
@@ -822,6 +867,7 @@ int main(int argc, char** argv) {
         testRecentProjects(*window, dataDir / "projects");
         testVideo(*window, dataDir / "video");
         testFont(*window, dataDir / "font");
+        testSlider(*window, dataDir / "slider");
         testHistory(*window, dataDir / "history");
         testMemoryGuard(*window, dataDir / "memory");
         app->remove_window(*window);