QMenu/QComboBox: Extract helper for determining the pop up geometry

Move the code returning whether a popup should use the full
screen to QStylePrivate and use for QMenu and QComboBox.

Task-number: QTBUG-73231
Change-Id: I1901ecedfa90edf16329ce3b13ef4abea5ab44e8
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/widgets/styles/qstyle.cpp

@@ -46,6 +46,7 @@
 #include "qstyleoption.h"
 #include "private/qstyle_p.h"
 #include "private/qguiapplication_p.h"
+#include <qpa/qplatformtheme.h>
 #ifndef QT_NO_DEBUG
 #include "qdebug.h"
 #endif
@@ -2447,6 +2448,13 @@ void QStyle::setProxy(QStyle *style)
     d->proxyStyle = style;
 }
 
+//Windows and KDE allow menus to cover the taskbar, while GNOME and macOS don't
+bool QStylePrivate::useFullScreenForPopup()
+{
+    auto theme = QGuiApplicationPrivate::platformTheme();
+    return theme && theme->themeHint(QPlatformTheme::UseFullScreenForPopupMenu).toBool();
+}
+
 QT_END_NAMESPACE
 
 #include "moc_qstyle.cpp"

src/widgets/styles/qstyle_p.h

@@ -67,6 +67,9 @@ class QStylePrivate: public QObjectPrivate
 public:
     inline QStylePrivate()
         : layoutSpacingIndex(-1), proxyStyle(0) {}
+
+    static bool useFullScreenForPopup();
+
     mutable int layoutSpacingIndex;
     QStyle *proxyStyle;
 };

src/widgets/widgets/qcombobox.cpp

@@ -80,6 +80,7 @@
 #if QT_CONFIG(effects)
 # include <private/qeffects_p.h>
 #endif
+#include <private/qstyle_p.h>
 #ifndef QT_NO_ACCESSIBILITY
 #include "qaccessible.h"
 #endif
@@ -261,16 +262,11 @@ void QComboBoxPrivate::_q_modelDestroyed()
     model = QAbstractItemModelPrivate::staticEmptyModel();
 }
 
-
-//Windows and KDE allows menus to cover the taskbar, while GNOME and Mac don't
 QRect QComboBoxPrivate::popupGeometry(int screen) const
 {
-    bool useFullScreenForPopupMenu = false;
-    if (const QPlatformTheme *theme = QGuiApplicationPrivate::platformTheme())
-        useFullScreenForPopupMenu = theme->themeHint(QPlatformTheme::UseFullScreenForPopupMenu).toBool();
-    return useFullScreenForPopupMenu ?
-           QDesktopWidgetPrivate::screenGeometry(screen) :
-           QDesktopWidgetPrivate::availableGeometry(screen);
+    return QStylePrivate::useFullScreenForPopup()
+        ? QDesktopWidgetPrivate::screenGeometry(screen)
+        : QDesktopWidgetPrivate::availableGeometry(screen);
 }
 
 bool QComboBoxPrivate::updateHoverControl(const QPoint &pos)

src/widgets/widgets/qmenu.cpp

@@ -78,6 +78,7 @@
 #include <private/qguiapplication_p.h>
 #include <qpa/qplatformtheme.h>
 #include <private/qdesktopwidget_p.h>
+#include <private/qstyle_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -307,29 +308,26 @@ int QMenuPrivate::scrollerHeight() const
     return qMax(QApplication::globalStrut().height(), q->style()->pixelMetric(QStyle::PM_MenuScrollerHeight, 0, q));
 }
 
-//Windows and KDE allow menus to cover the taskbar, while GNOME and Mac don't
+// Windows and KDE allow menus to cover the taskbar, while GNOME and macOS
+// don't. Torn-off menus are again different
+inline bool QMenuPrivate::useFullScreenForPopup() const
+{
+    return !tornoff && QStylePrivate::useFullScreenForPopup();
+}
+
 QRect QMenuPrivate::popupGeometry() const
 {
     Q_Q(const QMenu);
-    if (!tornoff && // Torn-off menus are different
-            QGuiApplicationPrivate::platformTheme() &&
-            QGuiApplicationPrivate::platformTheme()->themeHint(QPlatformTheme::UseFullScreenForPopupMenu).toBool()) {
-        return QDesktopWidgetPrivate::screenGeometry(q);
-    } else {
-        return QDesktopWidgetPrivate::availableGeometry(q);
-    }
+    return useFullScreenForPopup()
+        ? QDesktopWidgetPrivate::screenGeometry(q)
+        : QDesktopWidgetPrivate::availableGeometry(q);
 }
 
-//Windows and KDE allow menus to cover the taskbar, while GNOME and Mac don't
 QRect QMenuPrivate::popupGeometry(int screen) const
 {
-    if (!tornoff && // Torn-off menus are different
-            QGuiApplicationPrivate::platformTheme() &&
-            QGuiApplicationPrivate::platformTheme()->themeHint(QPlatformTheme::UseFullScreenForPopupMenu).toBool()) {
-        return QDesktopWidgetPrivate::screenGeometry(screen);
-    } else {
-        return QDesktopWidgetPrivate::availableGeometry(screen);
-    }
+    return useFullScreenForPopup()
+        ? QDesktopWidgetPrivate::screenGeometry(screen)
+        : QDesktopWidgetPrivate::availableGeometry(screen);
 }
 
 QVector<QPointer<QWidget> > QMenuPrivate::calcCausedStack() const

src/widgets/widgets/qmenu_p.h

@@ -343,6 +343,7 @@ public:
     void updateActionRects(const QRect &screen) const;
     QRect popupGeometry() const;
     QRect popupGeometry(int screen) const;
+    bool useFullScreenForPopup() const;
     int getLastVisibleAction() const;
 
     //selection