Linux: handle dark system themes nicely

yuzu's default theme doesn't specify everything, which is fine for
windows, but in linux anything unspecified is set to the users theme.

Symptoms of this are that a linux user with a dark theme won't think
to change the theme to a dark theme when first using yuzu

Idea here is to try and support arbitrary themes on linux.

preliminary work on a "default_dark" theme, used only as overlay
for any themes that are measured to be dark mode.

Other work done:

FreeDesktop standard icon names:
plus -> list-add
delete refresh, we use view-refresh

remove duplicated icons for qdarkstyle_midnight_blue
referencing icon aliases in the qrc files is the way to go

Note:
Dynamic style changing doesn't appear to work with AppImage

4 files changed, 77 insertions, 14 deletions

diff --git a/src/yuzu/game_list.cpp b/src/yuzu/game_list.cpp
index 041e6ac11..c4b1f65bd 100644
--- a/src/yuzu/game_list.cpp
+++ b/src/yuzu/game_list.cpp
@@ -286,7 +286,7 @@ void GameList::OnUpdateThemedIcons() {
         }
         case GameListItemType::AddDir:
             child->setData(
-                QIcon::fromTheme(QStringLiteral("plus"))
+                QIcon::fromTheme(QStringLiteral("list-add"))
                     .pixmap(icon_size)
                     .scaled(icon_size, icon_size, Qt::IgnoreAspectRatio, Qt::SmoothTransformation),
                 Qt::DecorationRole);
diff --git a/src/yuzu/game_list_p.h b/src/yuzu/game_list_p.h
index e7667cf60..0e19be22d 100644
--- a/src/yuzu/game_list_p.h
+++ b/src/yuzu/game_list_p.h
@@ -294,7 +294,7 @@ public:
 
         const int icon_size = UISettings::values.folder_icon_size.GetValue();
 
-        setData(QIcon::fromTheme(QStringLiteral("plus"))
+        setData(QIcon::fromTheme(QStringLiteral("list-add"))
                     .pixmap(icon_size)
                     .scaled(icon_size, icon_size, Qt::IgnoreAspectRatio, Qt::SmoothTransformation),
                 Qt::DecorationRole);
diff --git a/src/yuzu/main.cpp b/src/yuzu/main.cpp
index f8c234082..e473ac6da 100644
--- a/src/yuzu/main.cpp
+++ b/src/yuzu/main.cpp
@@ -257,6 +257,18 @@ static QString PrettyProductName() {
     return QSysInfo::prettyProductName();
 }
 
+bool GMainWindow::check_dark_mode() {
+#ifdef __linux__
+    const QPalette test_palette(qApp->palette());
+    const QColor text_color = test_palette.color(QPalette::Active, QPalette::Text);
+    const QColor window_color = test_palette.color(QPalette::Active, QPalette::Window);
+    return (text_color.value() > window_color.value());
+#else
+    // TODO: Windows
+    return false;
+#endif // __linux__
+}
+
 GMainWindow::GMainWindow(bool has_broken_vulkan)
     : ui{std::make_unique<Ui::MainWindow>()}, system{std::make_unique<Core::System>()},
       input_subsystem{std::make_shared<InputCommon::InputSubsystem>()},
@@ -274,6 +286,13 @@ GMainWindow::GMainWindow(bool has_broken_vulkan)
     ui->setupUi(this);
     statusBar()->hide();
 
+    // Check dark mode before a theme is loaded
+    os_dark_mode = check_dark_mode();
+    startup_icon_theme = QIcon::themeName();
+    // fallback can only be set once, colorful theme icons are okay on both light/dark
+    QIcon::setFallbackThemeName(QStringLiteral("colorful"));
+    QIcon::setFallbackSearchPaths(QStringList(QStringLiteral(":/icons")));
+
     default_theme_paths = QIcon::themeSearchPaths();
     UpdateUITheme();
 
@@ -3930,8 +3949,21 @@ void GMainWindow::filterBarSetChecked(bool state) {
     emit(OnToggleFilterBar());
 }
 
+static void AdjustLinkColor() {
+    QPalette new_pal(qApp->palette());
+    if (UISettings::IsDarkTheme()) {
+        new_pal.setColor(QPalette::Link, QColor(0, 190, 255, 255));
+    } else {
+        new_pal.setColor(QPalette::Link, QColor(0, 140, 200, 255));
+    }
+    if (qApp->palette().color(QPalette::Link) != new_pal.color(QPalette::Link)) {
+        qApp->setPalette(new_pal);
+    }
+}
+
 void GMainWindow::UpdateUITheme() {
-    const QString default_theme = QStringLiteral("default");
+    const QString default_theme =
+        QString::fromUtf8(UISettings::themes[static_cast<size_t>(Config::default_theme)].second);
     QString current_theme = UISettings::values.theme;
     QStringList theme_paths(default_theme_paths);
 
@@ -3939,6 +3971,23 @@ void GMainWindow::UpdateUITheme() {
         current_theme = default_theme;
     }
 
+#ifdef _WIN32
+    QIcon::setThemeName(current_theme);
+    AdjustLinkColor();
+#else
+    if (current_theme == QStringLiteral("default") || current_theme == QStringLiteral("colorful")) {
+        QIcon::setThemeName(current_theme == QStringLiteral("colorful") ? current_theme
+                                                                        : startup_icon_theme);
+        QIcon::setThemeSearchPaths(theme_paths);
+        if (check_dark_mode()) {
+            current_theme = QStringLiteral("default_dark");
+        }
+    } else {
+        QIcon::setThemeName(current_theme);
+        QIcon::setThemeSearchPaths(QStringList(QStringLiteral(":/icons")));
+        AdjustLinkColor();
+    }
+#endif
     if (current_theme != default_theme) {
         QString theme_uri{QStringLiteral(":%1/style.qss").arg(current_theme)};
         QFile f(theme_uri);
@@ -3961,17 +4010,6 @@ void GMainWindow::UpdateUITheme() {
         qApp->setStyleSheet({});
         setStyleSheet({});
     }
-
-    QPalette new_pal(qApp->palette());
-    if (UISettings::IsDarkTheme()) {
-        new_pal.setColor(QPalette::Link, QColor(0, 190, 255, 255));
-    } else {
-        new_pal.setColor(QPalette::Link, QColor(0, 140, 200, 255));
-    }
-    qApp->setPalette(new_pal);
-
-    QIcon::setThemeName(current_theme);
-    QIcon::setThemeSearchPaths(theme_paths);
 }
 
 void GMainWindow::LoadTranslation() {
@@ -4022,6 +4060,26 @@ void GMainWindow::SetDiscordEnabled([[maybe_unused]] bool state) {
     discord_rpc->Update();
 }
 
+void GMainWindow::changeEvent(QEvent* event) {
+#ifdef __linux__
+    // PaletteChange event appears to only reach so far into the GUI, explicitly asking to
+    // UpdateUITheme is a decent work around
+    if (event->type() == QEvent::PaletteChange) {
+        const QPalette test_palette(qApp->palette());
+        const QString current_theme = UISettings::values.theme;
+        // Keeping eye on QPalette::Window to avoid looping. QPalette::Text might be useful too
+        static QColor last_window_color;
+        const QColor window_color = test_palette.color(QPalette::Active, QPalette::Window);
+        if (last_window_color != window_color && (current_theme == QStringLiteral("default") ||
+                                                  current_theme == QStringLiteral("colorful"))) {
+            UpdateUITheme();
+        }
+        last_window_color = window_color;
+    }
+#endif // __linux__
+    QWidget::changeEvent(event);
+}
+
 #ifdef main
 #undef main
 #endif
diff --git a/src/yuzu/main.h b/src/yuzu/main.h
index 23b67a14e..2d1c8857b 100644
--- a/src/yuzu/main.h
+++ b/src/yuzu/main.h
@@ -251,6 +251,7 @@ private:
     bool ConfirmForceLockedExit();
     void RequestGameExit();
     void RequestGameResume();
+    void changeEvent(QEvent* event) override;
     void closeEvent(QCloseEvent* event) override;
 
 #ifdef __linux__
@@ -392,6 +393,10 @@ private:
     QTimer mouse_hide_timer;
     QTimer mouse_center_timer;
 
+    QString startup_icon_theme;
+    bool os_dark_mode = false;
+    bool check_dark_mode();
+
     // FS
     std::shared_ptr<FileSys::VfsFilesystem> vfs;
     std::unique_ptr<FileSys::ManualContentProvider> provider;