Wrong caching of opaque children in QWidget.

The opaque children cache was clipped to all the ancestors up to the
top-level, which means whenever a widget changes geometry all the
children must be invalidated. However, the bug was that we didn't
invalidate the children, and that is of course slow so we don't want
to do it either. A better solution is to only clip the children cache to the
widget itself (widget->rect() instead of widget->clipRect()), and we can
perfectly do this because the region we subtract the opaque children from is
already inside the clipRect().

Auto-test included.

Task-number: QTBUG-4245 (related to)

3 files changed, 51 insertions, 14 deletions

diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index 5fa9a92..1951ab2 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -1825,18 +1825,6 @@ void QWidgetPrivate::setDirtyOpaqueRegion()
         pd->setDirtyOpaqueRegion();
 }
 
-QRegion QWidgetPrivate::getOpaqueRegion() const
-{
-    Q_Q(const QWidget);
-
-    QRegion r = isOpaque ? q->rect() : getOpaqueChildren();
-    if (extra && extra->hasMask)
-        r &= extra->mask;
-    if (r.isEmpty())
-        return r;
-    return r & clipRect();
-}
-
 const QRegion &QWidgetPrivate::getOpaqueChildren() const
 {
     if (!dirtyOpaqueChildren)
@@ -1851,9 +1839,17 @@ const QRegion &QWidgetPrivate::getOpaqueChildren() const
             continue;
 
         const QPoint offset = child->geometry().topLeft();
-        that->opaqueChildren += child->d_func()->getOpaqueRegion().translated(offset);
+        QWidgetPrivate *childd = child->d_func();
+        QRegion r = childd->isOpaque ? child->rect() : childd->getOpaqueChildren();
+        if (childd->extra && childd->extra->hasMask)
+            r &= childd->extra->mask;
+        if (r.isEmpty())
+            continue;
+        r.translate(offset);
+        that->opaqueChildren += r;
     }
 
+    that->opaqueChildren &= q_func()->rect();
     that->dirtyOpaqueChildren = false;
 
     return that->opaqueChildren;
diff --git a/src/gui/kernel/qwidget_p.h b/src/gui/kernel/qwidget_p.h
index 159a3f2..5cea641 100644
--- a/src/gui/kernel/qwidget_p.h
+++ b/src/gui/kernel/qwidget_p.h
@@ -386,7 +386,6 @@ public:
     bool paintOnScreen() const;
     void invalidateGraphicsEffectsRecursively();
 
-    QRegion getOpaqueRegion() const;
     const QRegion &getOpaqueChildren() const;
     void setDirtyOpaqueRegion();
 
diff --git a/tests/auto/qwidget/tst_qwidget.cpp b/tests/auto/qwidget/tst_qwidget.cpp
index 050d1c5..9c421d1 100644
--- a/tests/auto/qwidget/tst_qwidget.cpp
+++ b/tests/auto/qwidget/tst_qwidget.cpp
@@ -332,6 +332,7 @@ private slots:
     void doubleRepaint();
 #ifndef Q_WS_MAC
     void resizeInPaintEvent();
+    void opaqueChildren();
 #endif
 
     void setMaskInResizeEvent();
@@ -8272,6 +8273,47 @@ void tst_QWidget::resizeInPaintEvent()
     // Make sure the resize triggers another update.
     QTRY_COMPARE(widget.numPaintEvents, 1);
 }
+
+void tst_QWidget::opaqueChildren()
+{
+    QWidget widget;
+    widget.resize(200, 200);
+
+    QWidget child(&widget);
+    child.setGeometry(-700, -700, 200, 200);
+
+    QWidget grandChild(&child);
+    grandChild.resize(200, 200);
+
+    QWidget greatGrandChild(&grandChild);
+    greatGrandChild.setGeometry(50, 50, 200, 200);
+    greatGrandChild.setPalette(Qt::red);
+    greatGrandChild.setAutoFillBackground(true); // Opaque child widget.
+
+    widget.show();
+#ifdef Q_WS_X11
+    qt_x11_wait_for_window_manager(&widget);
+#endif
+    QTest::qWait(100);
+
+    // Child, grandChild and greatGrandChild are outside the ancestor clip.
+    QRegion expectedOpaqueRegion(50, 50, 150, 150);
+    QCOMPARE(qt_widget_private(&grandChild)->getOpaqueChildren(), expectedOpaqueRegion);
+
+    // Now they are all inside the ancestor clip.
+    child.setGeometry(50, 50, 150, 150);
+    QCOMPARE(qt_widget_private(&grandChild)->getOpaqueChildren(), expectedOpaqueRegion);
+
+    // Set mask on greatGrandChild.
+    const QRegion mask(10, 10, 50, 50);
+    greatGrandChild.setMask(mask);
+    expectedOpaqueRegion &= mask.translated(50, 50);
+    QCOMPARE(qt_widget_private(&grandChild)->getOpaqueChildren(), expectedOpaqueRegion);
+
+    // Make greatGrandChild "transparent".
+    greatGrandChild.setAutoFillBackground(false);
+    QCOMPARE(qt_widget_private(&grandChild)->getOpaqueChildren(), QRegion());
+}
 #endif