Implement virtual void QPlatformWindow::setBackingStore()

QWidget re-uses an existing backing store. Platform windows depend on
being associated to a backing store, in case they become toplevel
windows. If a platform window gets deleted and re-created each time it
is shown or hidden, it has to be manually associated to the re-used
backing store.

This patch partly reverts fbf0aeea7d3b38ced7a16fcd5c3e2e9b45536292.
It removes Android specific code from QWidgetPrivate::create(), which
has been added to suppress re-using backing stores in the absence of
the new API.

Fixes: QTBUG-97482
Pick-to: 6.6
Change-Id: Iaa1b7652efa120ec1955914c0383e8ccd8a41429
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

3 files changed, 11 insertions, 2 deletions

diff --git a/src/platformsupport/fbconvenience/qfbscreen.cpp b/src/platformsupport/fbconvenience/qfbscreen.cpp
index e804488005..a5d87fec04 100644
--- a/src/platformsupport/fbconvenience/qfbscreen.cpp
+++ b/src/platformsupport/fbconvenience/qfbscreen.cpp
@@ -47,6 +47,7 @@ bool QFbScreen::event(QEvent *event)
 
 void QFbScreen::addWindow(QFbWindow *window)
 {
+    Q_ASSERT(window->backingStore());
     mWindowStack.prepend(window);
     if (!mPendingBackingStores.isEmpty()) {
         //check if we have a backing store for this window
diff --git a/src/platformsupport/fbconvenience/qfbwindow.cpp b/src/platformsupport/fbconvenience/qfbwindow.cpp
index 54716cc497..8df50a14da 100644
--- a/src/platformsupport/fbconvenience/qfbwindow.cpp
+++ b/src/platformsupport/fbconvenience/qfbwindow.cpp
@@ -3,9 +3,11 @@
 
 #include "qfbwindow_p.h"
 #include "qfbscreen_p.h"
+#include "qfbbackingstore_p.h"
 
 #include <QtGui/QScreen>
 #include <qpa/qwindowsysteminterface.h>
+#include <qpa/qplatformbackingstore.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -111,5 +113,11 @@ void QFbWindow::repaint(const QRegion &region)
     for (auto rect : region)
         platformScreen()->setDirty(rect.translated(topLeft));
 }
-
+void QFbWindow::setBackingStore(QPlatformBackingStore *store)
+{
+    Q_ASSERT(store);
+    Q_ASSERT_X(dynamic_cast<QFbBackingStore *>(store), __FUNCTION__,
+               "Argument is not a QFbBackingStore.");
+    mBackingStore = static_cast<QFbBackingStore *>(store);
+}
 QT_END_NAMESPACE
diff --git a/src/platformsupport/fbconvenience/qfbwindow_p.h b/src/platformsupport/fbconvenience/qfbwindow_p.h
index 8367a10bce..8848e9dcf8 100644
--- a/src/platformsupport/fbconvenience/qfbwindow_p.h
+++ b/src/platformsupport/fbconvenience/qfbwindow_p.h
@@ -41,7 +41,7 @@ public:
 
     WId winId() const override { return mWindowId; }
 
-    void setBackingStore(QFbBackingStore *store) { mBackingStore = store; }
+    void setBackingStore(QPlatformBackingStore *store) override;
     QFbBackingStore *backingStore() const { return mBackingStore; }
 
     QFbScreen *platformScreen() const;