Allow setting the QIcon fallback theme

This allows apps that know their icons are
in a given icon theme to set that theme as
fallback, so in case the user theme does
not include them, the icons can still be found.

This solves the problem of missing icons
that often happens when running KDE applications
on a GNOME desktop.

Change-Id: I4e5543d598012352a29ff79dab0357506d986b6d
Reviewed-by: Dominik Haumann <dhaumann@kde.org>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 15 insertions, 5 deletions

diff --git a/src/gui/image/qiconloader.cpp b/src/gui/image/qiconloader.cpp
index 1ea4f1340b..228de3adc3 100644
--- a/src/gui/image/qiconloader.cpp
+++ b/src/gui/image/qiconloader.cpp
@@ -60,7 +60,7 @@ QT_BEGIN_NAMESPACE
 Q_GLOBAL_STATIC(QIconLoader, iconLoaderInstance)
 
 /* Theme to use in last resort, if the theme does not have the icon, neither the parents  */
-static QString fallbackTheme()
+static QString systemFallbackThemeName()
 {
     if (const QPlatformTheme *theme = QGuiApplicationPrivate::platformTheme()) {
         const QVariant themeHint = theme->themeHint(QPlatformTheme::SystemIconFallbackThemeName);
@@ -117,7 +117,7 @@ void QIconLoader::ensureInitialized()
         m_systemTheme = systemThemeName();
 
         if (m_systemTheme.isEmpty())
-            m_systemTheme = fallbackTheme();
+            m_systemTheme = systemFallbackThemeName();
         if (qt_iconEngineFactoryLoader()->keyMap().key(QLatin1String("svg"), -1) != -1)
             m_supportsSvg = true;
     }
@@ -137,7 +137,7 @@ void QIconLoader::updateSystemTheme()
     if (m_userTheme.isEmpty()) {
         QString theme = systemThemeName();
         if (theme.isEmpty())
-            theme = fallbackTheme();
+            theme = fallbackThemeName();
         if (theme != m_systemTheme) {
             m_systemTheme = theme;
             invalidateKey();
@@ -151,6 +151,16 @@ void QIconLoader::setThemeName(const QString &themeName)
     invalidateKey();
 }
 
+QString QIconLoader::fallbackThemeName() const
+{
+    return m_userFallbackTheme.isEmpty() ? systemFallbackThemeName() : m_userFallbackTheme;
+}
+
+void QIconLoader::setFallbackThemeName(const QString &themeName)
+{
+    m_userFallbackTheme = themeName;
+}
+
 void QIconLoader::setThemeSearchPath(const QStringList &searchPaths)
 {
     m_iconDirs = searchPaths;
@@ -388,7 +398,7 @@ QIconTheme::QIconTheme(const QString &themeName)
 
         // Ensure a default platform fallback for all themes
         if (m_parents.isEmpty()) {
-            const QString fallback = fallbackTheme();
+            const QString fallback = QIconLoader::instance()->fallbackThemeName();
             if (!fallback.isEmpty())
                 m_parents.append(fallback);
         }
@@ -414,7 +424,7 @@ QThemeIconInfo QIconLoader::findIconHelper(const QString &themeName,
     if (!theme.isValid()) {
         theme = QIconTheme(themeName);
         if (!theme.isValid())
-            theme = QIconTheme(fallbackTheme());
+            theme = QIconTheme(fallbackThemeName());
     }
 
     const QStringList contentDirs = theme.contentDirs();