Fix rhi flush eval perf. and native window problems

This effectively reverts a4a51f6a641f4bf0a863251d6d3e026d81de6280
while solving the problem that change intended to fix by an
alternative approach: Swap the order of checks for rhi-based
flushing. Checking the widgets' wishes first was a mistake.  We should
first check what is forced, e.g. via the env.vars.  Then only move on
investigating the child widget hierarchy if there was nothing specific
requested.

This way having a QOpenGLWidget in a window and running with
QT_WIDGETS_RHI=1 QT_WIDGETS_RHI_BACKEND=vulkan will prioritize the
forced request (Vulkan) and so the QOpenGLWidget will gracefully not
render anything while printing the expected warning to tell what's
going on.

The expensive recursion plaguing the construction of larger widget
hierarchies is now avoided, that should no longer take seconds due to
walking the entire widget hierarchy of the top-level window every time
a new widget is added to it.

However, this then uncovered a set of problems concerning native child
widgets. The repaint manager seems to have an obvious mistake where
the usage of rhi (and so textures and whatnot) is decided based on
'widget' (which is either a top-level or a native child) instead of
'tlw' (which is the top-level with the backingstore). The usesRhiFlush
flag only really matters for a real top-level, not for native child
widgets.  The rhi-based flushing is tied to the backingstore, and the
backingstore comes from the top-level widget.

Finally, make the qopenglwidget autotest to actually exercise
something when it comes to QOpenGLWidgets (or their ancestors) turned
native.  The original code from a long time ago does not really test
native child widgets, because it turns the top-level into native which
is quite superfluous since the toplevel is backed by a native window
(and a backingstore) anyway.

Pick-to: 6.4
Task-number: QTBUG-105017
Fixes: QTBUG-108344
Fixes: QTBUG-108277
Change-Id: I1785b0ca627cf151aad06a5489f63874d787f087
Reviewed-by: Andy Nichols <andy.nichols@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

1 files changed, 125 insertions, 32 deletions

diff --git a/tests/auto/widgets/widgets/qopenglwidget/tst_qopenglwidget.cpp b/tests/auto/widgets/widgets/qopenglwidget/tst_qopenglwidget.cpp
index 523984e751..4d3699009f 100644
--- a/tests/auto/widgets/widgets/qopenglwidget/tst_qopenglwidget.cpp
+++ b/tests/auto/widgets/widgets/qopenglwidget/tst_qopenglwidget.cpp
@@ -529,39 +529,132 @@ void tst_QOpenGLWidget::nativeWindow()
 #ifdef Q_OS_ANDROID
     QSKIP("Crashes on Android, figure out why (QTBUG-102043)");
 #endif
-    QScopedPointer<ClearWidget> w(new ClearWidget(0, 800, 600));
-    w->resize(800, 600);
-    w->show();
-    w->winId();
-    QVERIFY(QTest::qWaitForWindowExposed(w.data()));
 
-    QImage image = w->grabFramebuffer();
-    QVERIFY(!image.isNull());
-    QCOMPARE(image.width(), w->width());
-    QCOMPARE(image.height(), w->height());
-    QVERIFY(image.pixel(30, 40) == qRgb(255, 0, 0));
-    QVERIFY(w->internalWinId());
-
-    // Now as a native child.
-    QWidget nativeParent;
-    nativeParent.resize(800, 600);
-    nativeParent.setAttribute(Qt::WA_NativeWindow);
-    ClearWidget *child = new ClearWidget(0, 800, 600);
-    child->setClearColor(0, 1, 0);
-    child->setParent(&nativeParent);
-    child->resize(400, 400);
-    child->move(23, 34);
-    nativeParent.show();
-    QVERIFY(QTest::qWaitForWindowExposed(&nativeParent));
-
-    QVERIFY(nativeParent.internalWinId());
-    QVERIFY(!child->internalWinId());
-
-    image = child->grabFramebuffer();
-    QVERIFY(!image.isNull());
-    QCOMPARE(image.width(), child->width());
-    QCOMPARE(image.height(), child->height());
-    QVERIFY(image.pixel(30, 40) == qRgb(0, 255, 0));
+    // NB these tests do not fully verify that native child widgets are fully
+    // functional since there is no guarantee that the content is composed and
+    // presented correctly as we can only do verification with
+    // grabFramebuffer() here which only exercises a part of the pipeline.
+
+    {
+        QScopedPointer<ClearWidget> w(new ClearWidget(nullptr, 800, 600));
+        w->resize(800, 600);
+        w->show();
+        w->winId();
+        QVERIFY(QTest::qWaitForWindowExposed(w.data()));
+
+        QImage image = w->grabFramebuffer();
+        QVERIFY(!image.isNull());
+        QCOMPARE(image.width(), w->width());
+        QCOMPARE(image.height(), w->height());
+        QVERIFY(image.pixel(30, 40) == qRgb(255, 0, 0));
+        QVERIFY(w->internalWinId());
+    }
+
+    // Now as a native child
+    {
+        QWidget topLevel;
+        topLevel.resize(800, 600);
+
+        ClearWidget *child = new ClearWidget(nullptr, 800, 600);
+        child->setParent(&topLevel);
+
+        // make it a native child (native window, but not top-level -> no backingstore)
+        child->winId();
+
+        child->setClearColor(0, 1, 0);
+        child->resize(400, 400);
+        child->move(23, 34);
+
+        topLevel.show();
+        QVERIFY(QTest::qWaitForWindowExposed(&topLevel));
+
+        QVERIFY(topLevel.internalWinId());
+        QVERIFY(child->internalWinId());
+
+        QImage image = child->grabFramebuffer();
+        QVERIFY(!image.isNull());
+        QCOMPARE(image.width(), child->width());
+        QCOMPARE(image.height(), child->height());
+        QVERIFY(image.pixel(30, 40) == qRgb(0, 255, 0));
+    }
+
+    // Now the same with WA_NativeWindow instead
+    {
+        QWidget topLevel;
+        topLevel.resize(800, 600);
+
+        ClearWidget *child = new ClearWidget(nullptr, 800, 600);
+        child->setParent(&topLevel);
+
+        // make it a native child (native window, but not top-level -> no backingstore)
+        child->setAttribute(Qt::WA_NativeWindow);
+
+        child->setClearColor(0, 1, 0);
+        child->resize(400, 400);
+        child->move(23, 34);
+
+        topLevel.show();
+        QVERIFY(QTest::qWaitForWindowExposed(&topLevel));
+
+        QVERIFY(child->internalWinId());
+
+        QImage image = child->grabFramebuffer();
+        QCOMPARE(image.width(), child->width());
+        QCOMPARE(image.height(), child->height());
+        QVERIFY(image.pixel(30, 40) == qRgb(0, 255, 0));
+    }
+
+    // Now as a child of a native child
+    {
+        QWidget topLevel;
+        topLevel.resize(800, 600);
+
+        QWidget *container = new QWidget(&topLevel);
+        // make it a native child (native window, but not top-level -> no backingstore)
+        container->winId();
+
+        ClearWidget *child = new ClearWidget(nullptr, 800, 600);
+        // set the parent separately, this is important, see next test case
+        child->setParent(container);
+        child->setClearColor(0, 1, 0);
+        child->resize(400, 400);
+        child->move(23, 34);
+
+        topLevel.show();
+        QVERIFY(QTest::qWaitForWindowExposed(&topLevel));
+
+        QVERIFY(topLevel.internalWinId());
+        QVERIFY(container->internalWinId());
+        QVERIFY(!child->internalWinId());
+
+        QImage image = child->grabFramebuffer();
+        QCOMPARE(image.width(), child->width());
+        QCOMPARE(image.height(), child->height());
+        QVERIFY(image.pixel(30, 40) == qRgb(0, 255, 0));
+    }
+
+    // Again as a child of a native child, but this time specifying the parent
+    // upon construction, not with an explicit setParent() call afterwards.
+    {
+        QWidget topLevel;
+        topLevel.resize(800, 600);
+        QWidget *container = new QWidget(&topLevel);
+        container->winId();
+        // parent it right away
+        ClearWidget *child = new ClearWidget(container, 800, 600);
+        child->setClearColor(0, 1, 0);
+        child->resize(400, 400);
+        child->move(23, 34);
+        topLevel.show();
+        QVERIFY(QTest::qWaitForWindowExposed(&topLevel));
+        QVERIFY(topLevel.internalWinId());
+        QVERIFY(container->internalWinId());
+        QVERIFY(!child->internalWinId());
+        QImage image = child->grabFramebuffer();
+        QCOMPARE(image.width(), child->width());
+        QCOMPARE(image.height(), child->height());
+        QVERIFY(image.pixel(30, 40) == qRgb(0, 255, 0));
+    }
 }
 
 static inline QString msgRgbMismatch(unsigned actual, unsigned expected)