QWidget::childAt for masked child widgets doesn't work properly

Problem was that we didn't take the children's effective mask
into account when checking whether a point was inside or not.

This commit is also an optimization since we no longer check the point
against the widget's rect twice. Furthermore, unnecessary
QRegion operations are completely avoided in the common case.

Auto tests included.

Task-number: QTBUG-7150
Reviewed-by: paul

1 files changed, 44 insertions, 31 deletions

diff --git a/src/gui/kernel/qwidget.cpp b/src/gui/kernel/qwidget.cpp
index ab84a54..492954a 100644
--- a/src/gui/kernel/qwidget.cpp
+++ b/src/gui/kernel/qwidget.cpp
@@ -67,6 +67,7 @@
 # include "qt_mac_p.h"
 # include "qt_cocoa_helpers_mac_p.h"
 # include "qmainwindow.h"
+# include "qtoolbar.h"
 #endif
 #if defined(Q_WS_QWS)
 # include "qwsdisplay_qws.h"
@@ -9716,46 +9717,58 @@ QWidget *QWidget::childAt(const QPoint &p) const
 
 QWidget *QWidgetPrivate::childAt_helper(const QPoint &p, bool ignoreChildrenInDestructor) const
 {
-    Q_Q(const QWidget);
+    if (children.isEmpty())
+        return 0;
+
 #ifdef Q_WS_MAC
+    Q_Q(const QWidget);
+    // Unified tool bars on the Mac require special handling since they live outside
+    // QMainWindow's geometry(). See commit: 35667fd45ada49269a5987c235fdedfc43e92bb8
     bool includeFrame = q->isWindow() && qobject_cast<const QMainWindow *>(q)
                         && static_cast<const QMainWindow *>(q)->unifiedTitleAndToolBarOnMac();
+    if (includeFrame)
+        return childAtRecursiveHelper(p, ignoreChildrenInDestructor, includeFrame);
 #endif
 
-    if (
-#ifdef Q_WS_MAC
-            !includeFrame &&
-#endif
-            !q->rect().contains(p))
+    if (!pointInsideRectAndMask(p))
         return 0;
+    return childAtRecursiveHelper(p, ignoreChildrenInDestructor);
+}
 
-    for (int i = children.size(); i > 0 ;) {
-        --i;
-        QWidget *w = qobject_cast<QWidget *>(children.at(i));
-        if (w && !w->isWindow() && !w->isHidden()
-                && (w->geometry().contains(p)
-#ifdef Q_WS_MAC
-                    || (includeFrame && w->geometry().contains(qt_mac_nativeMapFromParent(w, p)))
+QWidget *QWidgetPrivate::childAtRecursiveHelper(const QPoint &p, bool ignoreChildrenInDestructor, bool includeFrame) const
+{
+#ifndef Q_WS_MAC
+    Q_UNUSED(includeFrame);
 #endif
-               )) {
-            if (ignoreChildrenInDestructor && w->data->in_destructor)
-                continue;
-            if (w->testAttribute(Qt::WA_TransparentForMouseEvents))
-                continue;
-            QPoint childPoint = w->mapFromParent(p);
-#ifdef Q_WS_MAC
-            if (includeFrame && !w->geometry().contains(p))
-                childPoint = qt_mac_nativeMapFromParent(w, p);
-#endif
-            if (QWidget *t = w->d_func()->childAt_helper(childPoint, ignoreChildrenInDestructor))
-                return t;
-            // if WMouseNoMask is set the widget mask is ignored, if
-            // the widget has no mask then the WMouseNoMask flag has no
-            // effect
-            if (w->testAttribute(Qt::WA_MouseNoMask) || w->mask().contains(childPoint)
-                || w->mask().isEmpty())
-                return w;
+    for (int i = children.size() - 1; i >= 0; --i) {
+        QWidget *child = qobject_cast<QWidget *>(children.at(i));
+        if (!child || child->isWindow() || child->isHidden() || child->testAttribute(Qt::WA_TransparentForMouseEvents)
+            || (ignoreChildrenInDestructor && child->data->in_destructor)) {
+            continue;
         }
+
+        // Map the point 'p' from parent coordinates to child coordinates.
+        QPoint childPoint = p;
+#ifdef Q_WS_MAC
+        // 'includeFrame' is true if the child's parent is a top-level QMainWindow with an unified tool bar.
+        // An unified tool bar on the Mac lives outside QMainWindow's geometry(), so a normal
+        // QWidget::mapFromParent won't do the trick.
+        if (includeFrame && qobject_cast<QToolBar *>(child))
+            childPoint = qt_mac_nativeMapFromParent(child, p);
+        else
+#endif
+        childPoint -= child->data->crect.topLeft();
+
+        // Check if the point hits the child.
+        if (!child->d_func()->pointInsideRectAndMask(childPoint))
+            continue;
+
+        // Do the same for the child's descendants.
+        if (QWidget *w = child->d_func()->childAtRecursiveHelper(childPoint, ignoreChildrenInDestructor))
+            return w;
+
+        // We have found our target; namely the child at position 'p'.
+        return child;
     }
     return 0;
 }