Setting WA_TranslucentBackground after winid() is ineffective on Symbian.

Currently Symbian doesn't support semi-transparent EGL surfaces.
WA_TranslucentBackground attribute is ineffective if set after EGL
surface creation. To enable translucency in this case we need to
recreate backing store to get raster surface which supports translucency.

Task-number: QT-4416
Reviewed-by: Jason Barron
(cherry picked from commit d62e9f4a6fe199ae790b1561fd4ba9ea84bd4d1e)

1 files changed, 8 insertions, 0 deletions

diff --git a/src/gui/kernel/qwidget_s60.cpp b/src/gui/kernel/qwidget_s60.cpp
index 7f8fec7..8e4e99a 100644
--- a/src/gui/kernel/qwidget_s60.cpp
+++ b/src/gui/kernel/qwidget_s60.cpp
@@ -780,6 +780,14 @@ void QWidgetPrivate::s60UpdateIsOpaque()
         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")) {
+                // 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);
+            }
         }
     } else if (extra->topextra->nativeWindowTransparencyEnabled) {
         window->SetTransparentRegion(TRegionFix<1>());