Refactor theme plugin loading.

In the old implementation, the QPlatformIntegration was asked
for the theme first, so there was no way of overriding that
by a custom plugin. Also, there was a memory leak in case
the platform theme was actually created by a plugin.

QGuiApplication now asks the QPlatformIntegration for a list
of potential theme names first, tries to load them using
the plugin loader and finally invokes a factory method of
QPlatformIntegration in case that fails. The theme is now
owned by QGuiApplication.

In the XCB plugin, the environment variable DESKTOP_SESSION
is queried and appended to the list of themes, making it possible
to load plugins for other session types.

Change-Id: I1a4b4e061815bca16c65b23e591bb7563a3e44e2
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

5 files changed, 22 insertions, 11 deletions

diff --git a/src/plugins/platforms/windows/qwindowscontext.cpp b/src/plugins/platforms/windows/qwindowscontext.cpp
index e8050d5027..f61e40ef77 100644
--- a/src/plugins/platforms/windows/qwindowscontext.cpp
+++ b/src/plugins/platforms/windows/qwindowscontext.cpp
@@ -788,7 +788,8 @@ bool QWindowsContext::windowsProc(HWND hwnd, UINT message,
         QWindowSystemInterface::handleCloseEvent(platformWindow->window());
         return true;
     case QtWindows::ThemeChanged: // ### fixme: Compress these events?
-        QWindowsTheme::instance()->windowsThemeChanged(platformWindow->window());
+        if (QWindowsTheme *theme = QWindowsTheme::instance())
+            theme->windowsThemeChanged(platformWindow->window());
         return true;
     default:
         break;
diff --git a/src/plugins/platforms/windows/qwindowsintegration.cpp b/src/plugins/platforms/windows/qwindowsintegration.cpp
index 7510cded50..ee58a19ca9 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.cpp
+++ b/src/plugins/platforms/windows/qwindowsintegration.cpp
@@ -183,7 +183,6 @@ struct QWindowsIntegrationPrivate
     QOpenGLStaticContextPtr m_staticOpenGLContext;
     QWindowsInputContext m_inputContext;
     QWindowsAccessibility m_accessibility;
-    QWindowsTheme m_theme;
     QWindowsServices m_services;
 };
 
@@ -362,9 +361,16 @@ QAbstractEventDispatcher * QWindowsIntegration::guiThreadEventDispatcher() const
     return d->m_eventDispatcher;
 }
 
-QPlatformTheme *QWindowsIntegration::platformTheme() const
+QStringList QWindowsIntegration::themeNames() const
 {
-    return &d->m_theme;
+    return QStringList(QLatin1String(QWindowsTheme::name));
+}
+
+QPlatformTheme *QWindowsIntegration::createPlatformTheme(const QString &name) const
+{
+    if (name == QLatin1String(QWindowsTheme::name))
+        return new QWindowsTheme;
+    return QPlatformIntegration::createPlatformTheme(name);
 }
 
 QPlatformServices *QWindowsIntegration::services() const
diff --git a/src/plugins/platforms/windows/qwindowsintegration.h b/src/plugins/platforms/windows/qwindowsintegration.h
index 6dd65a02e4..20fd790bfe 100644
--- a/src/plugins/platforms/windows/qwindowsintegration.h
+++ b/src/plugins/platforms/windows/qwindowsintegration.h
@@ -69,7 +69,8 @@ public:
     virtual QPlatformAccessibility *accessibility() const;
     virtual QPlatformNativeInterface *nativeInterface() const;
     virtual QPlatformFontDatabase *fontDatabase() const;
-    virtual QPlatformTheme *platformTheme() const;
+    virtual QStringList themeNames() const;
+    virtual QPlatformTheme *createPlatformTheme(const QString &name) const;
     QPlatformServices *services() const;
     virtual QVariant styleHint(StyleHint hint) const;
 
diff --git a/src/plugins/platforms/windows/qwindowstheme.cpp b/src/plugins/platforms/windows/qwindowstheme.cpp
index f10595fa79..f3a9d91d00 100644
--- a/src/plugins/platforms/windows/qwindowstheme.cpp
+++ b/src/plugins/platforms/windows/qwindowstheme.cpp
@@ -229,8 +229,12 @@ static inline QPalette *menuBarPalette(const QPalette &menuPalette)
     return result;
 }
 
+const char *QWindowsTheme::name = "windows";
+QWindowsTheme *QWindowsTheme::m_instance = 0;
+
 QWindowsTheme::QWindowsTheme()
 {
+    m_instance = this;
     qFill(m_fonts, m_fonts + NFonts, static_cast<QFont *>(0));
     qFill(m_palettes, m_palettes + NPalettes, static_cast<QPalette *>(0));
     refresh();
@@ -240,11 +244,7 @@ QWindowsTheme::~QWindowsTheme()
 {
     clearPalettes();
     clearFonts();
-}
-
-QWindowsTheme *QWindowsTheme::instance()
-{
-    return static_cast<QWindowsTheme *>(QWindowsIntegration::instance()->platformTheme());
+    m_instance = 0;
 }
 
 static inline QStringList iconThemeSearchPaths()
diff --git a/src/plugins/platforms/windows/qwindowstheme.h b/src/plugins/platforms/windows/qwindowstheme.h
index 37346eed3a..7515a13a72 100644
--- a/src/plugins/platforms/windows/qwindowstheme.h
+++ b/src/plugins/platforms/windows/qwindowstheme.h
@@ -57,7 +57,7 @@ public:
     QWindowsTheme();
     ~QWindowsTheme();
 
-    static QWindowsTheme *instance();
+    static QWindowsTheme *instance() { return m_instance; }
 
     virtual bool usePlatformNativeDialog(DialogType type) const;
     virtual QPlatformDialogHelper *createPlatformDialogHelper(DialogType type) const;
@@ -69,6 +69,8 @@ public:
 
     void windowsThemeChanged(QWindow *window);
 
+    static const char *name;
+
 private:
     void refresh() { refreshPalettes(); refreshFonts(); }
     void clearPalettes();
@@ -76,6 +78,7 @@ private:
     void clearFonts();
     void refreshFonts();
 
+    static QWindowsTheme *m_instance;
     QPalette *m_palettes[NPalettes];
     QFont *m_fonts[NFonts];
 };