Let QPlatformTheme decide which engine QIcon::fromTheme uses

By default we still use QIconLoaderEngine but now platform theme plugins
have the opportunity to override that. It is in particular planned to be
used in a WIP platform theme plugin for KDE sessions.

Change-Id: I07a82dc91daea44709b3a790f3f6e2a7a090d108
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: David Faure (KDE) <faure@kde.org>
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>

3 files changed, 24 insertions, 1 deletions

diff --git a/src/gui/image/qicon.cpp b/src/gui/image/qicon.cpp
index dce902301c..6b91ead666 100644
--- a/src/gui/image/qicon.cpp
+++ b/src/gui/image/qicon.cpp
@@ -60,6 +60,7 @@
 
 #include "private/qhexstring_p.h"
 #include "private/qguiapplication_p.h"
+#include "qpa/qplatformtheme.h"
 
 #ifndef QT_NO_ICON
 QT_BEGIN_NAMESPACE
@@ -986,7 +987,10 @@ QIcon QIcon::fromTheme(const QString &name, const QIcon &fallback)
     if (qtIconCache()->contains(name)) {
         icon = *qtIconCache()->object(name);
     } else {
-        QIcon *cachedIcon  = new QIcon(new QIconLoaderEngine(name));
+        QPlatformTheme * const platformTheme = QGuiApplicationPrivate::platformTheme();
+        QIconEngine * const engine = platformTheme ? platformTheme->createIconEngine(name)
+                                                   : new QIconLoaderEngine(name);
+        QIcon *cachedIcon  = new QIcon(engine);
         qtIconCache()->insert(name, cachedIcon);
         icon = *cachedIcon;
     }
diff --git a/src/gui/kernel/qplatformtheme.cpp b/src/gui/kernel/qplatformtheme.cpp
index ceb95c51e8..9f5c789a6e 100644
--- a/src/gui/kernel/qplatformtheme.cpp
+++ b/src/gui/kernel/qplatformtheme.cpp
@@ -46,6 +46,7 @@
 #include <QtCore/qfileinfo.h>
 #include <qpalette.h>
 #include <qtextformat.h>
+#include <qiconloader_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -272,4 +273,19 @@ QPlatformSystemTrayIcon *QPlatformTheme::createPlatformSystemTrayIcon() const
 }
 #endif
 
+/*!
+   Factory function for the QIconEngine used by QIcon::fromTheme(). By default this
+   function returns a QIconLoaderEngine, but subclasses can reimplement it to
+   provide their own.
+
+   It is especially useful to benefit from some platform specific facilities or
+   optimizations like an inter-process cache in systems mostly built with Qt.
+
+   \since 5.1
+*/
+QIconEngine *QPlatformTheme::createIconEngine(const QString &iconName) const
+{
+    return new QIconLoaderEngine(iconName);
+}
+
 QT_END_NAMESPACE
diff --git a/src/gui/kernel/qplatformtheme.h b/src/gui/kernel/qplatformtheme.h
index 14e2dac19d..0e95321102 100644
--- a/src/gui/kernel/qplatformtheme.h
+++ b/src/gui/kernel/qplatformtheme.h
@@ -55,6 +55,7 @@
 
 QT_BEGIN_NAMESPACE
 
+class QIconEngine;
 class QMenu;
 class QMenuBar;
 class QPlatformMenuItem;
@@ -270,6 +271,8 @@ public:
     virtual QPixmap standardPixmap(StandardPixmap sp, const QSizeF &size) const;
     virtual QPixmap fileIconPixmap(const QFileInfo &fileInfo, const QSizeF &size) const;
 
+    virtual QIconEngine *createIconEngine(const QString &iconName) const;
+
     static QVariant defaultThemeHint(ThemeHint hint);
 };