Make wheelScrollLines a QStyleHint

The number of lines to scroll on a wheel click have previously been
a QPlatformTheme hint and QApplication setting, this patch moves it to
QStyleHint so it may be easier read by QGuiApplications.

Change-Id: I80673c7b99d78c6407b1202b3742e1cb5fef0583
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

src/gui/kernel/qplatformintegration.cpp

@@ -409,6 +409,8 @@ QVariant QPlatformIntegration::styleHint(StyleHint hint) const
         return QPlatformTheme::defaultThemeHint(QPlatformTheme::ItemViewActivateItemOnSingleClick);
     case UiEffects:
         return QPlatformTheme::defaultThemeHint(QPlatformTheme::UiEffects);
+    case WheelScrollLines:
+        return QPlatformTheme::defaultThemeHint(QPlatformTheme::WheelScrollLines);
     }
 
     return 0;

src/gui/kernel/qplatformintegration.h

@@ -157,7 +157,8 @@ public:
         TabFocusBehavior,
         ReplayMousePressOutsidePopup,
         ItemViewActivateItemOnSingleClick,
-        UiEffects
+        UiEffects,
+        WheelScrollLines,
     };
 
     virtual QVariant styleHint(StyleHint hint) const;

src/gui/kernel/qstylehints.cpp

@@ -78,6 +78,7 @@ public:
         , m_cursorFlashTime(-1)
         , m_tabFocusBehavior(-1)
         , m_uiEffects(-1)
+        , m_wheelScrollLines(-1)
         {}
 
     int m_mouseDoubleClickInterval;
@@ -88,6 +89,7 @@ public:
     int m_cursorFlashTime;
     int m_tabFocusBehavior;
     int m_uiEffects;
+    int m_wheelScrollLines;
 };
 
 /*!
@@ -495,4 +497,33 @@ void QStyleHints::setUseHoverEffects(bool useHoverEffects)
     emit useHoverEffectsChanged(useHoverEffects);
 }
 
+/*!
+    \property QStyleHints::wheelScrollLines
+    \brief Number of lines to scroll by default for each wheel click.
+
+    \since 5.9
+*/
+int QStyleHints::wheelScrollLines() const
+{
+    Q_D(const QStyleHints);
+    if (d->m_wheelScrollLines > 0)
+        return d->m_wheelScrollLines;
+    return themeableHint(QPlatformTheme::WheelScrollLines, QPlatformIntegration::WheelScrollLines).toInt();
+}
+
+/*!
+    Sets the \a wheelScrollLines.
+    \internal
+    \sa wheelScrollLines()
+    \since 5.9
+*/
+void QStyleHints::setWheelScrollLines(int scrollLines)
+{
+    Q_D(QStyleHints);
+    if (d->m_wheelScrollLines == scrollLines)
+        return;
+    d->m_wheelScrollLines = scrollLines;
+    emit wheelScrollLinesChanged(scrollLines);
+}
+
 QT_END_NAMESPACE

src/gui/kernel/qstylehints.h

@@ -71,6 +71,7 @@ class Q_GUI_EXPORT QStyleHints : public QObject
     Q_PROPERTY(Qt::TabFocusBehavior tabFocusBehavior READ tabFocusBehavior NOTIFY tabFocusBehaviorChanged FINAL)
     Q_PROPERTY(bool singleClickActivation READ singleClickActivation STORED false CONSTANT FINAL)
     Q_PROPERTY(bool useHoverEffects READ useHoverEffects WRITE setUseHoverEffects NOTIFY useHoverEffectsChanged FINAL)
+    Q_PROPERTY(int wheelScrollLines READ wheelScrollLines NOTIFY wheelScrollLinesChanged FINAL)
 
 public:
     void setMouseDoubleClickInterval(int mouseDoubleClickInterval);
@@ -99,6 +100,8 @@ public:
     bool singleClickActivation() const;
     bool useHoverEffects() const;
     void setUseHoverEffects(bool useHoverEffects);
+    int wheelScrollLines() const;
+    void setWheelScrollLines(int scrollLines);
 
 Q_SIGNALS:
     void cursorFlashTimeChanged(int cursorFlashTime);
@@ -109,6 +112,7 @@ Q_SIGNALS:
     void startDragTimeChanged(int startDragTime);
     void tabFocusBehaviorChanged(Qt::TabFocusBehavior tabFocusBehavior);
     void useHoverEffectsChanged(bool useHoverEffects);
+    void wheelScrollLinesChanged(int scrollLines);
 
 private:
     friend class QGuiApplication;

src/widgets/kernel/qapplication.cpp

@@ -408,7 +408,6 @@ QWidget *QApplicationPrivate::focus_widget = 0;        // has keyboard input foc
 QWidget *QApplicationPrivate::hidden_focus_widget = 0; // will get keyboard input focus after show()
 QWidget *QApplicationPrivate::active_window = 0;        // toplevel with keyboard focus
 #ifndef QT_NO_WHEELEVENT
-int QApplicationPrivate::wheel_scroll_lines;   // number of lines to scroll
 QPointer<QWidget> QApplicationPrivate::wheel_widget;
 #endif
 bool qt_in_tab_key_event = false;
@@ -642,19 +641,12 @@ void QApplicationPrivate::initialize()
     if (qEnvironmentVariableIntValue("QT_USE_NATIVE_WINDOWS") > 0)
         QCoreApplication::setAttribute(Qt::AA_NativeWindows);
 
-#ifndef QT_NO_WHEELEVENT
-    QApplicationPrivate::wheel_scroll_lines = 3;
-#endif
-
     if (qt_is_gui_used)
         initializeMultitouch();
 
     if (QApplication::desktopSettingsAware())
         if (const QPlatformTheme *theme = QGuiApplicationPrivate::platformTheme()) {
             QApplicationPrivate::enabledAnimations = theme->themeHint(QPlatformTheme::UiEffects).toInt();
-#ifndef QT_NO_WHEELEVENT
-            QApplicationPrivate::wheel_scroll_lines = theme->themeHint(QPlatformTheme::WheelScrollLines).toInt();
-#endif
         }
 
     is_app_running = true; // no longer starting up
@@ -4049,16 +4041,18 @@ int QApplication::keyboardInputInterval()
     or \l{QAbstractItemView::ScrollPerPixel}{scroll one pixel}.
 
     By default, this property has a value of 3.
+
+    \sa QStyleHints::wheelScrollLines()
 */
 #ifndef QT_NO_WHEELEVENT
 int QApplication::wheelScrollLines()
 {
-    return QApplicationPrivate::wheel_scroll_lines;
+    return styleHints()->wheelScrollLines();
 }
 
 void QApplication::setWheelScrollLines(int lines)
 {
-    QApplicationPrivate::wheel_scroll_lines = lines;
+    styleHints()->setWheelScrollLines(lines);
 }
 #endif