Fixes scrolling horizontally with a mouse wheel over sliders.

When scrolling horizontally over sliders the slider should go to the right,
which means the value of the slider should increase. However in Qt scrolling
with a mouse wheel horizontally means the delta value is negative, which is
wrong. So changed the delta to be inversed.

Reviewed-by: Richard Moe Gustavsen

3 files changed, 57 insertions, 27 deletions

diff --git a/src/gui/widgets/qabstractslider.cpp b/src/gui/widgets/qabstractslider.cpp
index 2874647..f119a4f 100644
--- a/src/gui/widgets/qabstractslider.cpp
+++ b/src/gui/widgets/qabstractslider.cpp
@@ -688,51 +688,64 @@ void QAbstractSlider::sliderChange(SliderChange)
     update();
 }
 
-
-/*!
-    \reimp
-*/
-#ifndef QT_NO_WHEELEVENT
-void QAbstractSlider::wheelEvent(QWheelEvent * e)
+bool QAbstractSliderPrivate::scrollByDelta(Qt::Orientation orientation, Qt::KeyboardModifiers modifiers, int delta)
 {
-    Q_D(QAbstractSlider);
-    e->ignore();
-
+    Q_Q(QAbstractSlider);
     int stepsToScroll = 0;
-    qreal offset = qreal(e->delta()) / 120;
+    // in Qt scrolling to the right gives negative values.
+    if (orientation == Qt::Horizontal)
+        delta = -delta;
+    qreal offset = qreal(delta) / 120;
 
-    if ((e->modifiers() & Qt::ControlModifier) || (e->modifiers() & Qt::ShiftModifier)) {
+    if ((modifiers & Qt::ControlModifier) || (modifiers & Qt::ShiftModifier)) {
         // Scroll one page regardless of delta:
-        stepsToScroll = qBound(-d->pageStep, int(offset * d->pageStep), d->pageStep);
-        d->offset_accumulated = 0;
+        stepsToScroll = qBound(-pageStep, int(offset * pageStep), pageStep);
+        offset_accumulated = 0;
     } else {
         // Calculate how many lines to scroll. Depending on what delta is (and 
         // offset), we might end up with a fraction (e.g. scroll 1.3 lines). We can
         // only scroll whole lines, so we keep the reminder until next event.
-        qreal stepsToScrollF = offset * QApplication::wheelScrollLines() * d->effectiveSingleStep();
+        qreal stepsToScrollF = offset * QApplication::wheelScrollLines() * effectiveSingleStep();
         // Check if wheel changed direction since last event:
-        if (d->offset_accumulated != 0 && (offset / d->offset_accumulated) < 0)
-            d->offset_accumulated = 0;
+        if (offset_accumulated != 0 && (offset / offset_accumulated) < 0)
+            offset_accumulated = 0;
 
-        d->offset_accumulated += stepsToScrollF;
-        stepsToScroll = qBound(-d->pageStep, int(d->offset_accumulated), d->pageStep);
-        d->offset_accumulated -= int(d->offset_accumulated);
+        offset_accumulated += stepsToScrollF;
+        stepsToScroll = qBound(-pageStep, int(offset_accumulated), pageStep);
+        offset_accumulated -= int(offset_accumulated);
         if (stepsToScroll == 0)
-            return;
+            return false;
     }
 
-    if (d->invertedControls)
+    if (invertedControls)
         stepsToScroll = -stepsToScroll;
 
-    int prevValue = d->value;
-    d->position = d->overflowSafeAdd(stepsToScroll); // value will be updated by triggerAction()
-    triggerAction(SliderMove);
+    int prevValue = value;
+    position = overflowSafeAdd(stepsToScroll); // value will be updated by triggerAction()
+    q->triggerAction(QAbstractSlider::SliderMove);
 
-    if (prevValue == d->value)
-        d->offset_accumulated = 0;
-    else
+    if (prevValue == value) {
+        offset_accumulated = 0;
+        return false;
+    }
+    return true;
+}
+
+/*!
+    \reimp
+*/
+#ifndef QT_NO_WHEELEVENT
+void QAbstractSlider::wheelEvent(QWheelEvent * e)
+{
+    Q_D(QAbstractSlider);
+    e->ignore();
+    if (e->orientation() != d->orientation && !rect().contains(e->pos()))
+        return;
+    int delta = e->delta();
+    if (d->scrollByDelta(e->orientation(), e->modifiers(), delta))
         e->accept();
 }
+
 #endif
 #ifdef QT_KEYPAD_NAVIGATION
 /*!
diff --git a/src/gui/widgets/qabstractslider_p.h b/src/gui/widgets/qabstractslider_p.h
index 6cde468..6e6ff6e 100644
--- a/src/gui/widgets/qabstractslider_p.h
+++ b/src/gui/widgets/qabstractslider_p.h
@@ -138,6 +138,7 @@ public:
         }
         q->triggerAction(repeatAction);
     }
+    bool scrollByDelta(Qt::Orientation orientation, Qt::KeyboardModifiers modifiers, int delta);
 };
 
 QT_END_NAMESPACE
diff --git a/src/gui/widgets/qscrollbar.cpp b/src/gui/widgets/qscrollbar.cpp
index 73ce122..3eed3a9 100644
--- a/src/gui/widgets/qscrollbar.cpp
+++ b/src/gui/widgets/qscrollbar.cpp
@@ -521,6 +521,22 @@ bool QScrollBar::event(QEvent *event)
     if (const QHoverEvent *he = static_cast<const QHoverEvent *>(event))
         d_func()->updateHoverControl(he->pos());
         break;
+    case QEvent::Wheel: {
+        // override wheel event without adding virtual function override
+        QWheelEvent *ev = static_cast<QWheelEvent *>(event);
+        int delta = ev->delta();
+        // scrollbar is a special case - in vertical mode it reaches minimum
+        // value in the upper position, however QSlider's minimum value is on
+        // the bottom. So we need to invert a value, but since the scrollbar is
+        // inverted by default, we need to inverse the delta value for the
+        // horizontal orientation.
+        if (ev->orientation() == Qt::Horizontal)
+            delta = -delta;
+        Q_D(QScrollBar);
+        if (d->scrollByDelta(ev->orientation(), ev->modifiers(), delta))
+            event->accept();
+        return true;
+    }
     default:
         break;
     }