QOpenGLCompositorBackingStore: ensure backing store on flushed windows

When the first QEglFSWindow got created for a QWindow, a backing store
was created with it and associated to the new QEglFSWindow. When the
window was hidden on the platform screen, the QEglFSWindow got deleted
and re-created when it was supposed to be shown.
The re-created QEglFSWindow was no longer associated to the backing
store. It was therefore not rendered on the screen.

=> ensure that the backing store is re-associated to the QEglFSWindow,
corrsponding to the QWindow argument passed to flush().

No autotest is added, because the fix is purely visual.
The widgets/menus example can be used to test the functionality
manually (see bug reports).

Fixes: QTBUG-115196
Fixes: QTBUG-116769
Pick-to: 6.6 6.5 6.2
Change-Id: I92ce2e8f7e76bd2d26e713a4d20612d079fb4717
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/plugins/platforms/eglfs/api/qeglfswindow_p.h b/src/plugins/platforms/eglfs/api/qeglfswindow_p.h
index d111042040..e51cd69f3d 100644
--- a/src/plugins/platforms/eglfs/api/qeglfswindow_p.h
+++ b/src/plugins/platforms/eglfs/api/qeglfswindow_p.h
@@ -70,8 +70,8 @@ public:
     bool isRaster() const;
 
 #ifndef QT_NO_OPENGL
-    QOpenGLCompositorBackingStore *backingStore() { return m_backingStore; }
-    void setBackingStore(QOpenGLCompositorBackingStore *backingStore);
+    QOpenGLCompositorBackingStore *backingStore() const override { return m_backingStore; }
+    void setBackingStore(QOpenGLCompositorBackingStore *backingStore) override;
     QWindow *sourceWindow() const override;
     const QPlatformTextureList *textures() const override;
     void endCompositing() override;