Add palette() and further hints to QtGui/QPlatformTheme.

- Move palette() from deprecated QtWidgets/QGuiPlatformPlugin
  to  QtGui/QPlatformTheme, Make it return a const * since
  QPalette does not have isNull().
- Initialize QGuiApplication::palette() and
  QApplication::systemPalette() from it.
- Do not initialize QPalette from QGuiApplication::palette()
  unless app_pal is non-null (default to Qt::black if it is 0).
  This avoids initialization order crashes/recursions in the
  QPA plugin. Streamline initialization function.
- Remove styleName(), systemIconThemeName() and iconSearchPaths()
  from QGuiPlatformPlugin and re-add them as
  QPlatformTheme::themeHint().
- Remove styleHint() from QGuiPlatformPlugin, add it to
  QPlatformTheme::themeHint().
- Add UNIX themes with factory function (Generic,
  KDE, Gnome), taking it from Qt 4.8 code (stripping the
  KDE 3 code).
- Implement Windows palettes.

Task-number: QTBUG-24204

Change-Id: Ie27ec035df4f84c42deaffc4816b2e53ce705462
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 5f50fe343a..9f8186424e 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -48,6 +48,7 @@
 #include "qplatformfontdatabase_qpa.h"
 #include "qplatformwindow_qpa.h"
 #include "qplatformnativeinterface_qpa.h"
+#include "qplatformtheme_qpa.h"
 
 #include <QtCore/QAbstractEventDispatcher>
 #include <QtCore/private/qcoreapplication_p.h>
@@ -1383,6 +1384,9 @@ QClipboard * QGuiApplication::clipboard()
 QPalette QGuiApplication::palette()
 {
     if (!QGuiApplicationPrivate::app_pal)
+        if (const QPalette *themePalette = QGuiApplicationPrivate::platformTheme()->palette())
+            QGuiApplicationPrivate::app_pal = new QPalette(*themePalette);
+    if (!QGuiApplicationPrivate::app_pal)
         QGuiApplicationPrivate::app_pal = new QPalette(Qt::black);
     return *QGuiApplicationPrivate::app_pal;
 }