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>

1 files changed, 4 insertions, 1 deletions

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];
 };