Allow horizontal scrolling with a mouse wheel for QListView

Convert vertical wheel events to horizontal for two cases of
the items layout when vertical scrolling is impossible:
1) TopToBottom flow with wrapping
2) LeftToRight flow without wrapping

Do it only for pure vertical events to avoid a mess for such
devices as touchpads or Apple Mouse.

[ChangeLog][QtWidgets][Important Behavior Changes] Allow
horizontal scrolling with a vertical mouse wheel for QListView.

Task-number: QTBUG-37007
Change-Id: Ie2525153fa7b443d27ca08cc5f5d4d7ecdb8c183
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

2 files changed, 34 insertions, 0 deletions

diff --git a/src/widgets/itemviews/qlistview.cpp b/src/widgets/itemviews/qlistview.cpp
index b7a4ec3925..29a6629bcd 100644
--- a/src/widgets/itemviews/qlistview.cpp
+++ b/src/widgets/itemviews/qlistview.cpp
@@ -53,6 +53,8 @@
 
 QT_BEGIN_NAMESPACE
 
+extern bool qt_sendSpontaneousEvent(QObject *receiver, QEvent *event);
+
 /*!
     \class QListView
 
@@ -796,6 +798,35 @@ void QListView::mouseReleaseEvent(QMouseEvent *e)
     }
 }
 
+#ifndef QT_NO_WHEELEVENT
+/*!
+  \reimp
+*/
+void QListView::wheelEvent(QWheelEvent *e)
+{
+    Q_D(QListView);
+    if (e->orientation() == Qt::Vertical) {
+        if (e->angleDelta().x() == 0
+            && ((d->flow == TopToBottom && d->wrap) || (d->flow == LeftToRight && !d->wrap))
+            && d->vbar->minimum() == 0 && d->vbar->maximum() == 0) {
+            QPoint pixelDelta(e->pixelDelta().y(), e->pixelDelta().x());
+            QPoint angleDelta(e->angleDelta().y(), e->angleDelta().x());
+            QWheelEvent hwe(e->pos(), e->globalPos(), pixelDelta, angleDelta, e->delta(),
+                            Qt::Horizontal, e->buttons(), e->modifiers(), e->phase());
+            if (e->spontaneous())
+                qt_sendSpontaneousEvent(d->hbar, &hwe);
+            else
+                QApplication::sendEvent(d->hbar, &hwe);
+            e->setAccepted(hwe.isAccepted());
+        } else {
+            QApplication::sendEvent(d->vbar, e);
+        }
+    } else {
+        QApplication::sendEvent(d->hbar, e);
+    }
+}
+#endif // QT_NO_WHEELEVENT
+
 /*!
   \reimp
 */
diff --git a/src/widgets/itemviews/qlistview.h b/src/widgets/itemviews/qlistview.h
index f62c96067f..ac65a47d9f 100644
--- a/src/widgets/itemviews/qlistview.h
+++ b/src/widgets/itemviews/qlistview.h
@@ -146,6 +146,9 @@ protected:
 
     void mouseMoveEvent(QMouseEvent *e) Q_DECL_OVERRIDE;
     void mouseReleaseEvent(QMouseEvent *e) Q_DECL_OVERRIDE;
+#ifndef QT_NO_WHEELEVENT
+    void wheelEvent(QWheelEvent *e) Q_DECL_OVERRIDE;
+#endif
 
     void timerEvent(QTimerEvent *e) Q_DECL_OVERRIDE;
     void resizeEvent(QResizeEvent *e) Q_DECL_OVERRIDE;