Read and use WheelScrollLines configuration on KDE

Qt supports changing the default lines a scroll wheel click scroll, but
wasn't trying to read the system settings. The patch adds support for
platform themes to set the default.

Change-Id: I53fdcec7984941d1d1285d927d70460356613f81
Reviewed-by: Kevin Ottens <kevin.ottens@kdab.com>
Reviewed-by: David Faure <david.faure@kdab.com>

src/gui/kernel/qplatformtheme.cpp

@@ -513,6 +513,8 @@ QVariant QPlatformTheme::defaultThemeHint(ThemeHint hint)
             int dist = qgetenv("QT_DBL_CLICK_DIST").toInt(&ok);
             return QVariant(ok ? dist : 5);
         }
+    case WheelScrollLines:
+        return QVariant(3);
     }
     return QVariant();
 }

src/gui/kernel/qplatformtheme.h

@@ -109,7 +109,8 @@ public:
         DialogSnapToDefaultButton,
         ContextMenuOnMouseRelease,
         MousePressAndHoldInterval,
-        MouseDoubleClickDistance
+        MouseDoubleClickDistance,
+        WheelScrollLines
     };
 
     enum DialogType {

src/platformsupport/themes/genericunix/qgenericunixthemes.cpp

@@ -178,6 +178,7 @@ public:
         , toolButtonStyle(Qt::ToolButtonTextBesideIcon)
         , toolBarIconSize(0)
         , singleClick(true)
+        , wheelScrollLines(3)
     { }
 
     static QString kdeGlobals(const QString &kdeDir)
@@ -201,6 +202,7 @@ public:
     int toolButtonStyle;
     int toolBarIconSize;
     bool singleClick;
+    int wheelScrollLines;
 };
 
 void QKdeThemePrivate::refresh()
@@ -250,6 +252,10 @@ void QKdeThemePrivate::refresh()
             toolButtonStyle = Qt::ToolButtonTextUnderIcon;
     }
 
+    const QVariant wheelScrollLinesValue = readKdeSetting(QStringLiteral("KDE/WheelScrollLines"), kdeDirs, kdeSettings);
+    if (wheelScrollLinesValue.isValid())
+        wheelScrollLines = wheelScrollLinesValue.toInt();
+
     // Read system font, ignore 'smallestReadableFont'
     if (QFont *systemFont = kdeFont(readKdeSetting(QStringLiteral("font"), kdeDirs, kdeSettings)))
         resources.fonts[QPlatformTheme::SystemFont] = systemFont;
@@ -436,6 +442,8 @@ QVariant QKdeTheme::themeHint(QPlatformTheme::ThemeHint hint) const
         return QVariant(int(KdeKeyboardScheme));
     case QPlatformTheme::ItemViewActivateItemOnSingleClick:
         return QVariant(d->singleClick);
+    case QPlatformTheme::WheelScrollLines:
+        return QVariant(d->wheelScrollLines);
     default:
         break;
     }

src/widgets/kernel/qapplication.cpp

@@ -666,8 +666,12 @@ void QApplicationPrivate::initialize()
         initializeMultitouch();
 
     if (QApplication::desktopSettingsAware())
-        if (const QPlatformTheme *theme = QGuiApplicationPrivate::platformTheme())
+        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
 }