Always recreate backing store when TLW transparency changes

When using either the opengl or openvg graphics system on Symbian,
if a TLW is made transparent, the widget switches to using raster
rendering, because EGL surface transparency is currently not
supported by the platform.

This patch enables the reverse to occur: when the widget is
subsequently made opaque, rendering switches back to using GL/VG.

Task-number: QTBUG-21211
Reviewed-by: Jani Hautakangas
Reviewed-by: Laszlo Agocs
Reviewed-by: Sami Merila

4 files changed, 101 insertions, 27 deletions

diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index 8e8266c..bda0885 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -2238,10 +2238,16 @@ void QWidgetPrivate::updateIsOpaque()
 #endif
 
 #ifdef Q_WS_S60
-    if (q->windowType() == Qt::Dialog && q->testAttribute(Qt::WA_TranslucentBackground)
-                && S60->avkonComponentsSupportTransparency) {
-        setOpaque(false);
-        return;
+    if (q->testAttribute(Qt::WA_TranslucentBackground)) {
+        if (q->windowType() & Qt::Dialog || q->windowType() & Qt::Popup) {
+            if (S60->avkonComponentsSupportTransparency) {
+                setOpaque(false);
+                return;
+            }
+        } else {
+            setOpaque(false);
+            return;
+        }
     }
 #endif
 
@@ -2261,11 +2267,16 @@ void QWidgetPrivate::updateIsOpaque()
     }
 
     if (q->isWindow() && !q->testAttribute(Qt::WA_NoSystemBackground)) {
+#ifdef Q_WS_S60
+        setOpaque(true);
+        return;
+#else
         const QBrush &windowBrush = q->palette().brush(QPalette::Window);
         if (windowBrush.style() != Qt::NoBrush && windowBrush.isOpaque()) {
             setOpaque(true);
             return;
         }
+#endif
     }
     setOpaque(false);
 }
@@ -10845,11 +10856,14 @@ void QWidget::setAttribute(Qt::WidgetAttribute attribute, bool on)
         }
         break;
     case Qt::WA_TranslucentBackground:
+#if defined(Q_OS_SYMBIAN)
+        setAttribute(Qt::WA_NoSystemBackground, on);
+#else
         if (on) {
             setAttribute(Qt::WA_NoSystemBackground);
             d->updateIsTranslucent();
         }
-
+#endif
         break;
     case Qt::WA_AcceptTouchEvents:
 #if defined(Q_WS_WIN) || defined(Q_WS_MAC) || defined(Q_OS_SYMBIAN)
diff --git a/src/gui/kernel/qwidget_p.h b/src/gui/kernel/qwidget_p.h
index e30497c..caa6454 100644
--- a/src/gui/kernel/qwidget_p.h
+++ b/src/gui/kernel/qwidget_p.h
@@ -228,6 +228,7 @@ struct QTLWExtra {
     uint inExpose : 1; // Prevents drawing recursion
     uint nativeWindowTransparencyEnabled : 1; // Tracks native window transparency
     uint forcedToRaster : 1;
+    uint noSystemRotationDisabled : 1;
 #endif
 };
 
diff --git a/src/gui/kernel/qwidget_s60.cpp b/src/gui/kernel/qwidget_s60.cpp
index e80eced..e12dfa7 100644
--- a/src/gui/kernel/qwidget_s60.cpp
+++ b/src/gui/kernel/qwidget_s60.cpp
@@ -820,19 +820,12 @@ void QWidgetPrivate::setConstraints_sys()
 void QWidgetPrivate::s60UpdateIsOpaque()
 {
     Q_Q(QWidget);
-
     if (!q->testAttribute(Qt::WA_WState_Created))
         return;
-
     const bool writeAlpha = extraData()->nativePaintMode == QWExtra::BlitWriteAlpha;
-    if (!q->testAttribute(Qt::WA_TranslucentBackground) && !writeAlpha)
-        return;
     const bool requireAlphaChannel = !isOpaque || writeAlpha;
-
     createTLExtra();
-
     RWindow *const window = static_cast<RWindow *>(q->effectiveWinId()->DrawableWindow());
-
 #ifdef Q_SYMBIAN_SEMITRANSPARENT_BG_SURFACE
     if (QApplicationPrivate::instance()->useTranslucentEGLSurfaces
             && !extra->topextra->forcedToRaster) {
@@ -841,25 +834,47 @@ void QWidgetPrivate::s60UpdateIsOpaque()
         return;
     }
 #endif
+    const bool recreateBackingStore = extra->topextra->backingStore.data() && (
+                                          QApplicationPrivate::graphics_system_name == QLatin1String("openvg") ||
+                                          QApplicationPrivate::graphics_system_name == QLatin1String("opengl")
+                                      );
     if (requireAlphaChannel) {
-        const TDisplayMode displayMode = static_cast<TDisplayMode>(window->SetRequiredDisplayMode(EColor16MA));
-        if (window->SetTransparencyAlphaChannel() == KErrNone) {
+        window->SetRequiredDisplayMode(EColor16MA);
+        if (window->SetTransparencyAlphaChannel() == KErrNone)
             window->SetBackgroundColor(TRgb(255, 255, 255, 0));
-            extra->topextra->nativeWindowTransparencyEnabled = 1;
-            if (extra->topextra->backingStore.data() && (
-                    QApplicationPrivate::graphics_system_name == QLatin1String("openvg")
-                    || QApplicationPrivate::graphics_system_name == QLatin1String("opengl"))) {
-                // Semi-transparent EGL surfaces aren't supported. We need to
-                // recreate backing store to get translucent surface (raster surface).
-                extra->topextra->backingStore.create(q);
-                extra->topextra->backingStore.registerWidget(q);
-                // FixNativeOrientation() will not work without an EGL surface.
+    } else {
+        if (recreateBackingStore) {
+            // Clear the UI surface to ensure that the EGL surface content is visible
+            CWsScreenDevice *screenDevice = S60->screenDevice(q);
+            QScopedPointer<CWindowGc> gc(new CWindowGc(screenDevice));
+            const int err = gc->Construct();
+            if (!err) {
+                gc->Activate(*window);
+                window->BeginRedraw();
+                gc->SetDrawMode(CWindowGc::EDrawModeWriteAlpha);
+                gc->SetBrushColor(TRgb(0, 0, 0, 0));
+                gc->Clear(TRect(0, 0, q->width(), q->height()));
+                window->EndRedraw();
+            }
+        }
+        if (extra->topextra->nativeWindowTransparencyEnabled)
+            window->SetTransparentRegion(TRegionFix<1>());
+    }
+    extra->topextra->nativeWindowTransparencyEnabled = requireAlphaChannel;
+    if (recreateBackingStore) {
+        extra->topextra->backingStore.create(q);
+        extra->topextra->backingStore.registerWidget(q);
+        bool noSystemRotationDisabled = false;
+        if (requireAlphaChannel) {
+            if (q->testAttribute(Qt::WA_SymbianNoSystemRotation)) {
+                // FixNativeOrientation() will not work without an EGL surface
                 q->setAttribute(Qt::WA_SymbianNoSystemRotation, false);
+                noSystemRotationDisabled = true;
             }
+        } else {
+            q->setAttribute(Qt::WA_SymbianNoSystemRotation, extra->topextra->noSystemRotationDisabled);
         }
-    } else if (extra->topextra->nativeWindowTransparencyEnabled) {
-        window->SetTransparentRegion(TRegionFix<1>());
-        extra->topextra->nativeWindowTransparencyEnabled = 0;
+        extra->topextra->noSystemRotationDisabled = noSystemRotationDisabled;
     }
 }
 
@@ -1020,6 +1035,7 @@ void QWidgetPrivate::createTLSysExtra()
     extra->topextra->inExpose = 0;
     extra->topextra->nativeWindowTransparencyEnabled = 0;
     extra->topextra->forcedToRaster = 0;
+    extra->topextra->noSystemRotationDisabled = 0;
 }
 
 void QWidgetPrivate::deleteTLSysExtra()
diff --git a/tests/auto/qwidget/tst_qwidget.cpp b/tests/auto/qwidget/tst_qwidget.cpp
index 43dd077..2161f99 100644
--- a/tests/auto/qwidget/tst_qwidget.cpp
+++ b/tests/auto/qwidget/tst_qwidget.cpp
@@ -397,6 +397,9 @@ private slots:
     void minimizedWindowModeTransitions();
     void normalWindowModeTransitions();
     void focusSwitchClosesPopupMenu();
+#if !defined(Q_SYMBIAN_SEMITRANSPARENT_BG_SURFACE)
+    void opacityChangeCausesBackingStoreRecreation();
+#endif
 #endif
 
     void focusProxyAndInputMethods();
@@ -10336,7 +10339,47 @@ void tst_QWidget::focusSwitchClosesPopupMenu()
     mainWindow.activateWindow();
     QVERIFY(!CEikonEnv::Static()->AppUiFactory()->MenuBar()->IsDisplayed());
 }
-#endif
+
+#if !defined(Q_SYMBIAN_SEMITRANSPARENT_BG_SURFACE)
+class OpacityChangeWidget : public QWidget
+{
+public:
+    OpacityChangeWidget() : m_paintEngineType(QPaintEngine::MaxUser) { }
+    void paintEvent(QPaintEvent *)
+    {
+        QPainter painter(this);
+        m_paintEngineType = painter.paintEngine()->type();
+    }
+    QPaintEngine::Type paintEngineType() const { return m_paintEngineType; }
+private:
+    QPaintEngine::Type m_paintEngineType;
+};
+
+void tst_QWidget::opacityChangeCausesBackingStoreRecreation()
+{
+    OpacityChangeWidget w;
+    w.show();
+    QTest::qWaitForWindowShown(&w);
+    const QPaintEngine::Type type = w.paintEngineType();
+    if (QPaintEngine::OpenGL != type && QPaintEngine::OpenVG != type) {
+        QSKIP("Test case is only valid when using opengl or openvg graphics system", SkipAll);
+    } else {
+        if (QApplicationPrivate::instance()->useTranslucentEGLSurfaces) {
+            QSKIP("Test case is only valid when EGL surface transparency is not supported", SkipAll);
+        } else {
+            // Making window transparent should force switch to raster graphics system
+            w.setAttribute(Qt::WA_TranslucentBackground, true);
+            w.repaint();
+            QCOMPARE(w.paintEngineType(), QPaintEngine::Raster);
+            // Making window opaque should cause switch back to previous graphics system
+            w.setAttribute(Qt::WA_TranslucentBackground, false);
+            w.repaint();
+            QCOMPARE(w.paintEngineType(), type);
+        }
+    }
+}
+#endif // !Q_SYMBIAN_SEMITRANSPARENT_BG_SURFACE
+#endif // Q_OS_SYMBIAN
 
 class InputContextTester : public QInputContext
 {