QWidgetWindow: fix enter/leave events not sent due to fractional scaling

If widget A starts at y=0 and widget B starts at y=19, when the mouse
moves from y=15 to y=18.6667, the code was doing childAt(p) with a
rounded QPoint y=19 and finding B, but then the relative coord for B
was set to -0.33333 so B wasn't under the mouse and didn't get an enter
event (and since it's now the "last receiver", it doesn't get one later
either when y is bigger).

Add QWidget::childAt(QPointF) to fix this.

Fixes: QTBUG-128391
Pick-to: 6.8
Change-Id: I76d4b711a8297648780bdd079eb67405ab12be14
Reviewed-by: Volker Hilsheimer <[email protected]>

6 files changed, 38 insertions, 21 deletions

diff --git a/src/widgets/kernel/qapplication.cpp b/src/widgets/kernel/qapplication.cpp
index 5e1d7923197..89d451589a8 100644
--- a/src/widgets/kernel/qapplication.cpp
+++ b/src/widgets/kernel/qapplication.cpp
@@ -2253,8 +2253,8 @@ bool QApplicationPrivate::modalState()
 /*
    \internal
 */
-QWidget *QApplicationPrivate::pickMouseReceiver(QWidget *candidate, const QPoint &windowPos,
-                                                QPoint *pos, QEvent::Type type,
+QWidget *QApplicationPrivate::pickMouseReceiver(QWidget *candidate, const QPointF &windowPos,
+                                                QPointF *pos, QEvent::Type type,
                                                 Qt::MouseButtons buttons, QWidget *buttonDown,
                                                 QWidget *alienWidget)
 {
diff --git a/src/widgets/kernel/qapplication_p.h b/src/widgets/kernel/qapplication_p.h
index 7de9f54b587..5f1d4ef13c3 100644
--- a/src/widgets/kernel/qapplication_p.h
+++ b/src/widgets/kernel/qapplication_p.h
@@ -168,7 +168,7 @@ public:
     static QString styleSheet;
 #endif
     static QPointer<QWidget> leaveAfterRelease;
-    static QWidget *pickMouseReceiver(QWidget *candidate, const QPoint &windowPos, QPoint *pos,
+    static QWidget *pickMouseReceiver(QWidget *candidate, const QPointF &windowPos, QPointF *pos,
                                       QEvent::Type type, Qt::MouseButtons buttons,
                                       QWidget *buttonDown, QWidget *alienWidget);
     static bool sendMouseEvent(QWidget *receiver, QMouseEvent *event, QWidget *alienWidget,
diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index 8b9513e2dd3..dcf53f0e84d 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -10453,10 +10453,23 @@ bool QWidget::hasHeightForWidth() const
 
 QWidget *QWidget::childAt(const QPoint &p) const
 {
+    return d_func()->childAt_helper(QPointF(p), false);
+}
+
+/*!
+    \overload
+    \since 6.8
+
+    Returns the visible child widget at point \a p in the widget's own
+    coordinate system.
+*/
+
+QWidget *QWidget::childAt(const QPointF &p) const
+{
     return d_func()->childAt_helper(p, false);
 }
 
-QWidget *QWidgetPrivate::childAt_helper(const QPoint &p, bool ignoreChildrenInDestructor) const
+QWidget *QWidgetPrivate::childAt_helper(const QPointF &p, bool ignoreChildrenInDestructor) const
 {
     if (children.isEmpty())
         return nullptr;
@@ -10466,7 +10479,7 @@ QWidget *QWidgetPrivate::childAt_helper(const QPoint &p, bool ignoreChildrenInDe
     return childAtRecursiveHelper(p, ignoreChildrenInDestructor);
 }
 
-QWidget *QWidgetPrivate::childAtRecursiveHelper(const QPoint &p, bool ignoreChildrenInDestructor) const
+QWidget *QWidgetPrivate::childAtRecursiveHelper(const QPointF &p, bool ignoreChildrenInDestructor) const
 {
     for (int i = children.size() - 1; i >= 0; --i) {
         QWidget *child = qobject_cast<QWidget *>(children.at(i));
@@ -10476,7 +10489,7 @@ QWidget *QWidgetPrivate::childAtRecursiveHelper(const QPoint &p, bool ignoreChil
         }
 
         // Map the point 'p' from parent coordinates to child coordinates.
-        QPoint childPoint = p;
+        QPointF childPoint = p;
         childPoint -= child->data->crect.topLeft();
 
         // Check if the point hits the child.
diff --git a/src/widgets/kernel/qwidget.h b/src/widgets/kernel/qwidget.h
index 7ee4412d881..faf2b31a832 100644
--- a/src/widgets/kernel/qwidget.h
+++ b/src/widgets/kernel/qwidget.h
@@ -627,6 +627,7 @@ public:
     static QWidget *find(WId);
     inline QWidget *childAt(int x, int y) const;
     QWidget *childAt(const QPoint &p) const;
+    QWidget *childAt(const QPointF &p) const;
 
     void setAttribute(Qt::WidgetAttribute, bool on = true);
     inline bool testAttribute(Qt::WidgetAttribute) const;
@@ -799,7 +800,7 @@ template <> inline const QWidget *qobject_cast<const QWidget*>(const QObject *o)
 #endif // !Q_QDOC
 
 inline QWidget *QWidget::childAt(int ax, int ay) const
-{ return childAt(QPoint(ax, ay)); }
+{ return childAt(QPointF(ax, ay)); }
 
 inline Qt::WindowType QWidget::windowType() const
 { return static_cast<Qt::WindowType>((data->window_flags & Qt::WindowType_Mask).toInt()); }
diff --git a/src/widgets/kernel/qwidget_p.h b/src/widgets/kernel/qwidget_p.h
index 7394bcdbbf8..f8ac13ebb74 100644
--- a/src/widgets/kernel/qwidget_p.h
+++ b/src/widgets/kernel/qwidget_p.h
@@ -420,9 +420,9 @@ public:
     bool setMinimumSize_helper(int &minw, int &minh);
     bool setMaximumSize_helper(int &maxw, int &maxh);
     void setConstraints_sys();
-    bool pointInsideRectAndMask(const QPoint &) const;
-    QWidget *childAt_helper(const QPoint &, bool) const;
-    QWidget *childAtRecursiveHelper(const QPoint &p, bool) const;
+    bool pointInsideRectAndMask(const QPointF &) const;
+    QWidget *childAt_helper(const QPointF &, bool) const;
+    QWidget *childAtRecursiveHelper(const QPointF &p, bool) const;
     void updateGeometry_helper(bool forceUpdate);
 
     void getLayoutItemMargins(int *left, int *top, int *right, int *bottom) const;
@@ -885,11 +885,14 @@ inline void QWidgetPrivate::setSharedPainter(QPainter *painter)
     x->sharedPainter = painter;
 }
 
-inline bool QWidgetPrivate::pointInsideRectAndMask(const QPoint &p) const
+inline bool QWidgetPrivate::pointInsideRectAndMask(const QPointF &p) const
 {
     Q_Q(const QWidget);
-    return q->rect().contains(p) && (!extra || !extra->hasMask || q->testAttribute(Qt::WA_MouseNoMask)
-                                     || extra->mask.contains(p));
+    // Use QRectF::contains so that (0, -0.1) isn't in, with p.toPoint() it would be
+    // The adjusted matches QRect semantics: (160,160) isn't contained in QRect(0, 0, 160, 160)
+    return QRectF(q->rect().adjusted(0, 0, -1, -1)).contains(p)
+            && (!extra || !extra->hasMask || q->testAttribute(Qt::WA_MouseNoMask)
+                || extra->mask.contains(p.toPoint() /* incorrect for the -0.1 case */));
 }
 
 inline QWidgetRepaintManager *QWidgetPrivate::maybeRepaintManager() const
diff --git a/src/widgets/kernel/qwidgetwindow.cpp b/src/widgets/kernel/qwidgetwindow.cpp
index 46871d0da16..e2f1776780d 100644
--- a/src/widgets/kernel/qwidgetwindow.cpp
+++ b/src/widgets/kernel/qwidgetwindow.cpp
@@ -450,7 +450,7 @@ void QWidgetWindow::handleEnterLeaveEvent(QEvent *event)
         }
     } else {
         const QEnterEvent *ee = static_cast<QEnterEvent *>(event);
-        QWidget *child = m_widget->childAt(ee->position().toPoint());
+        QWidget *child = m_widget->childAt(ee->position());
         QWidget *receiver = child ? child : m_widget.data();
         QWidget *leave = nullptr;
         if (QApplicationPrivate::inPopupMode() && receiver == m_widget
@@ -513,7 +513,7 @@ void QWidgetWindow::handleMouseEvent(QMouseEvent *event)
         if (activePopupWidget != m_widget)
             mapped = activePopupWidget->mapFromGlobal(event->globalPosition());
         bool releaseAfter = false;
-        QWidget *popupChild  = activePopupWidget->childAt(mapped.toPoint());
+        QWidget *popupChild = activePopupWidget->childAt(mapped);
 
         if (activePopupWidget != qt_popup_down) {
             qt_button_down = nullptr;
@@ -601,8 +601,8 @@ void QWidgetWindow::handleMouseEvent(QMouseEvent *event)
         return;
 
     // which child should have it?
-    QWidget *widget = m_widget->childAt(event->position().toPoint());
-    QPoint mapped = event->position().toPoint();
+    QWidget *widget = m_widget->childAt(event->position());
+    QPointF mapped = event->position();
 
     if (!widget)
         widget = m_widget;
@@ -611,7 +611,7 @@ void QWidgetWindow::handleMouseEvent(QMouseEvent *event)
     if (event->type() == QEvent::MouseButtonPress && initialPress)
         qt_button_down = widget;
 
-    QWidget *receiver = QApplicationPrivate::pickMouseReceiver(m_widget, event->scenePosition().toPoint(), &mapped, event->type(), event->buttons(),
+    QWidget *receiver = QApplicationPrivate::pickMouseReceiver(m_widget, event->scenePosition(), &mapped, event->type(), event->buttons(),
                                                                qt_button_down, widget);
     if (!receiver)
         return;
@@ -637,7 +637,7 @@ void QWidgetWindow::handleMouseEvent(QMouseEvent *event)
     if (event->type() == QGuiApplicationPrivate::contextMenuEventType()
         && event->button() == Qt::RightButton
         && m_widget->rect().contains(event->position().toPoint())) {
-        QContextMenuEvent e(QContextMenuEvent::Mouse, mapped, event->globalPosition().toPoint(), event->modifiers());
+        QContextMenuEvent e(QContextMenuEvent::Mouse, mapped.toPoint(), event->globalPosition().toPoint(), event->modifiers());
         QGuiApplication::forwardEvent(receiver, &e, event);
         if (e.isAccepted())
             event->accept();
@@ -867,7 +867,7 @@ void QWidgetWindow::handleWheelEvent(QWheelEvent *event)
     }
 
     // which child should have it?
-    QWidget *widget = rootWidget->childAt(pos.toPoint());
+    QWidget *widget = rootWidget->childAt(pos);
 
     if (!widget)
         widget = rootWidget;
@@ -1076,7 +1076,7 @@ void QWidgetWindow::handleTabletEvent(QTabletEvent *event)
     QWidget *widget = qt_tablet_target;
 
     if (!widget) {
-        widget = m_widget->childAt(event->position().toPoint());
+        widget = m_widget->childAt(event->position());
         if (!widget)
             widget = m_widget;
         if (event->type() == QEvent::TabletPress)