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>

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
 */

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;

tests/auto/widgets/itemviews/qlistview/tst_qlistview.cpp

@@ -38,6 +38,7 @@
 #include <qapplication.h>
 #include <qlistview.h>
 #include <private/qlistview_p.h>
+#include <private/qcoreapplication_p.h>
 #include <qlistwidget.h>
 #include <qitemdelegate.h>
 #include <qstandarditemmodel.h>
@@ -148,6 +149,7 @@ private slots:
     void testScrollToWithHidden();
     void testViewOptions();
     void taskQTBUG_39902_mutualScrollBars();
+    void horizontalScrollingByVerticalWheelEvents();
 };
 
 // Testing get/set functions
@@ -2372,5 +2374,52 @@ void tst_QListView::taskQTBUG_39902_mutualScrollBars()
     QTest::qWait(100);
 }
 
+void tst_QListView::horizontalScrollingByVerticalWheelEvents()
+{
+    QListView lv;
+    lv.setWrapping(true);
+
+    TestDelegate *delegate = new TestDelegate(&lv);
+    delegate->m_sizeHint = QSize(100, 100);
+    lv.setItemDelegate(delegate);
+
+    QtTestModel model;
+    model.colCount = 1;
+    model.rCount = 100;
+
+    lv.setModel(&model);
+
+    lv.resize(300, 300);
+    lv.show();
+    QTest::qWaitForWindowExposed(&lv);
+
+    QPoint globalPos = lv.geometry().center();
+    QPoint pos = lv.viewport()->geometry().center();
+
+    QWheelEvent wheelDownEvent(pos, globalPos, QPoint(0, 0), QPoint(0, -120), -120, Qt::Vertical, 0, 0);
+    QWheelEvent wheelUpEvent(pos, globalPos, QPoint(0, 0), QPoint(0, 120), 120, Qt::Vertical, 0, 0);
+    QWheelEvent wheelLeftDownEvent(pos, globalPos, QPoint(0, 0), QPoint(120, -120), -120, Qt::Vertical, 0, 0);
+
+    int hValue = lv.horizontalScrollBar()->value();
+    QApplication::sendEvent(lv.viewport(), &wheelDownEvent);
+    QVERIFY(lv.horizontalScrollBar()->value() > hValue);
+
+    QApplication::sendEvent(lv.viewport(), &wheelUpEvent);
+    QVERIFY(lv.horizontalScrollBar()->value() == hValue);
+
+    QApplication::sendEvent(lv.viewport(), &wheelLeftDownEvent);
+    QVERIFY(lv.horizontalScrollBar()->value() == hValue);
+
+    // ensure that vertical wheel events are not converted when vertical
+    // scroll bar is not visible but vertical scrolling is possible
+    lv.setWrapping(false);
+    lv.setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
+    QApplication::processEvents();
+
+    int vValue = lv.verticalScrollBar()->value();
+    QApplication::sendEvent(lv.viewport(), &wheelDownEvent);
+    QVERIFY(lv.verticalScrollBar()->value() > vValue);
+}
+
 QTEST_MAIN(tst_QListView)
 #include "tst_qlistview.moc"