Display combobox popup on the correct screen

Display QCompoBox popups on the correct screen, also
when the parent window spans multiple screens. In this
case, QWidget::screen() will return the main screen for the
window, which will not necessarily be the screen at
the combobox popup position.

Change-Id: Ib8a8163a757f7b849883b833fbde27a1e01af49a
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/widgets/kernel/qwidget_p.h

@@ -51,6 +51,8 @@
 // We mean it.
 //
 
+
+
 #include <QtWidgets/private/qtwidgetsglobal_p.h>
 #include "QtWidgets/qwidget.h"
 #include "private/qobject_p.h"
@@ -498,19 +500,45 @@ public:
 #endif
         return rect;
     }
+
     static QRect screenGeometry(const QWidget *widget)
     {
-        QRect rect = graphicsViewParentRect(widget);
-        if (rect.isNull())
-            rect = widget->screen()->geometry();
-        return rect;
+        return screenGeometry(widget, QPoint(), false);
     }
+
     static QRect availableScreenGeometry(const QWidget *widget)
+    {
+        return availableScreenGeometry(widget, QPoint(), false);
+    }
+
+    static QRect screenGeometry(const QWidget *widget, const QPoint &globalPosition, bool hasPosition = true)
     {
         QRect rect = graphicsViewParentRect(widget);
-        if (rect.isNull())
-            rect = widget->screen()->availableGeometry();
-        return rect;
+        if (!rect.isNull())
+            return rect;
+
+        QScreen *screen = nullptr;
+        if (hasPosition)
+            screen = widget->screen()->virtualSiblingAt(globalPosition);
+        if (!screen)
+            screen = widget->screen();
+
+        return screen->geometry();
+    }
+
+    static QRect availableScreenGeometry(const QWidget *widget, const QPoint &globalPosition, bool hasPosition = true)
+    {
+        QRect rect = graphicsViewParentRect(widget);
+        if (!rect.isNull())
+            return rect;
+
+        QScreen *screen = nullptr;
+        if (hasPosition)
+            screen = widget->screen()->virtualSiblingAt(globalPosition);
+        if (!screen)
+            screen = widget->screen();
+
+        return screen->availableGeometry();
     }
 
     inline void setRedirected(QPaintDevice *replacement, const QPoint &offset)

src/widgets/widgets/qcombobox.cpp

@@ -319,12 +319,12 @@ void QComboBoxPrivate::trySetValidIndex()
         setCurrentIndex(QModelIndex());
 }
 
-QRect QComboBoxPrivate::popupGeometry() const
+QRect QComboBoxPrivate::popupGeometry(const QPoint &globalPosition) const
 {
     Q_Q(const QComboBox);
     return QStylePrivate::useFullScreenForPopup()
-        ? QWidgetPrivate::screenGeometry(q)
-        : QWidgetPrivate::availableScreenGeometry(q);
+        ? QWidgetPrivate::screenGeometry(q, globalPosition)
+        : QWidgetPrivate::availableScreenGeometry(q, globalPosition);
 }
 
 bool QComboBoxPrivate::updateHoverControl(const QPoint &pos)
@@ -2612,7 +2612,7 @@ void QComboBox::showPopup()
     QComboBoxPrivateContainer* container = d->viewContainer();
     QRect listRect(style->subControlRect(QStyle::CC_ComboBox, &opt,
                                          QStyle::SC_ComboBoxListBoxPopup, this));
-    QRect screen = d->popupGeometry();
+    QRect screen = d->popupGeometry(mapToGlobal(listRect.topLeft()));
 
     QPoint below = mapToGlobal(listRect.bottomLeft());
     int belowHeight = screen.bottom() - below.y();

src/widgets/widgets/qcombobox_p.h

@@ -371,7 +371,7 @@ public:
     void updateArrow(QStyle::StateFlag state);
     bool updateHoverControl(const QPoint &pos);
     void trySetValidIndex();
-    QRect popupGeometry() const;
+    QRect popupGeometry(const QPoint &globalPos) const;
     QStyle::SubControl newHoverControl(const QPoint &pos);
     int computeWidthHint() const;
     QSize recomputeSizeHint(QSize &sh) const;