Set sharedPainter correctly for QGraphicsEffect

Autotest is taken from the previously reverted 8b1377f. Task-number: QTBUG-60231 Change-Id: I44dd79cba22b6baefdd6d95c176790bef0b7eafe Reviewed-by: Andy Nichols <andy.nichols@qt.io>
sailfishos · Dec 12, 2017 · 7257862 · 7257862
1 parent 6a5ca72
commit 7257862
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Showing 2 changed files with 23 additions and 2 deletions.
diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
@@ -5528,11 +5528,11 @@ void QWidgetPrivate::drawWidget(QPaintDevice *pdev, const QRegion &rgn, const QP
                 setSystemClip(pdev, rgn.translated(offset));
                 QPainter p(pdev);
                 p.translate(offset);
-                context.painter = &p;
+                context.painter = context.sharedPainter = &p;
                 graphicsEffect->draw(&p);
                 setSystemClip(pdev, QRegion());
             } else {
-                context.painter = sharedPainter;
+                context.painter = context.sharedPainter = sharedPainter;
                 if (sharedPainter->worldTransform() != sourced->lastEffectTransform) {
                     sourced->invalidateCache();
                     sourced->lastEffectTransform = sharedPainter->worldTransform();

diff --git a/tests/auto/widgets/effects/qgraphicseffect/tst_qgraphicseffect.cpp b/tests/auto/widgets/effects/qgraphicseffect/tst_qgraphicseffect.cpp
@@ -52,6 +52,7 @@ private slots:
     void boundingRect2();
     void draw();
     void opacity();
+    void nestedOpaqueOpacity();
     void grayscale();
     void colorize();
     void drawPixmapItem();
@@ -407,6 +408,26 @@ void tst_QGraphicsEffect::opacity()
     QCOMPARE(effect->m_opacity, qreal(0.5));
 }
 
+void tst_QGraphicsEffect::nestedOpaqueOpacity()
+{
+    // QTBUG-60231: Nesting widgets with a QGraphicsEffect on a toplevel with
+    // QGraphicsOpacityEffect caused crashes due to constructing several
+    // QPainter instances on a device in the fast path for
+    // QGraphicsOpacityEffect::opacity=1
+    QWidget topLevel;
+    topLevel.setWindowTitle(QTest::currentTestFunction());
+    topLevel.resize(320, 200);
+    QGraphicsOpacityEffect *opacityEffect = new QGraphicsOpacityEffect;
+    opacityEffect->setOpacity(1);
+    topLevel.setGraphicsEffect(opacityEffect);
+    QWidget *child = new QWidget(&topLevel);
+    child->resize(topLevel.size() / 2);
+    QGraphicsDropShadowEffect *childEffect = new QGraphicsDropShadowEffect;
+    child->setGraphicsEffect(childEffect);
+    topLevel.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&topLevel));
+}
+
 void tst_QGraphicsEffect::grayscale()
 {
     if (qApp->desktop()->depth() < 24)