Improve interaction between snapping and sections

* Use velocity to prefer snapping in the active direction.
* Calculate snap based on where the item is, rather than where
  the section is.

Change-Id: I2531501dbe0a58f26f20bc3e719e435185e047a5
Task-number: QTBUG-67051
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

3 files changed, 134 insertions, 11 deletions

diff --git a/src/quick/items/qquicklistview.cpp b/src/quick/items/qquicklistview.cpp
index 540805ac28..908801ce1c 100644
--- a/src/quick/items/qquicklistview.cpp
+++ b/src/quick/items/qquicklistview.cpp
@@ -515,8 +515,8 @@ QString QQuickListViewPrivate::sectionAt(int modelIndex)
 
 qreal QQuickListViewPrivate::snapPosAt(qreal pos)
 {
-    if (FxViewItem *snapItem = snapItemAt(pos))
-        return snapItem->position();
+    if (FxListItemSG *snapItem = static_cast<FxListItemSG*>(snapItemAt(pos)))
+        return snapItem->itemPosition();
     if (visibleItems.count()) {
         qreal firstPos = (*visibleItems.constBegin())->position();
         qreal endPos = (*(--visibleItems.constEnd()))->position();
@@ -530,22 +530,35 @@ qreal QQuickListViewPrivate::snapPosAt(qreal pos)
 
 FxViewItem *QQuickListViewPrivate::snapItemAt(qreal pos)
 {
+    const qreal velocity = orient == QQuickListView::Vertical ? vData.velocity : hData.velocity;
     FxViewItem *snapItem = nullptr;
+    FxViewItem *prevItem = nullptr;
     qreal prevItemSize = 0;
     for (FxViewItem *item : qAsConst(visibleItems)) {
         if (item->index == -1)
             continue;
-        qreal itemTop = item->position();
-        if (highlight && itemTop >= pos && item->endPosition() <= pos + highlight->size())
+
+        const FxListItemSG *listItem = static_cast<FxListItemSG *>(item);
+        qreal itemTop = listItem->position();
+        qreal itemSize = listItem->size();
+        if (highlight && itemTop >= pos && listItem->endPosition() <= pos + highlight->size())
             return item;
 
+        if (listItem->section() && velocity > 0) {
+            if (itemTop + listItem->sectionSize() / 2 >= pos && itemTop - prevItemSize / 2 < pos)
+                snapItem = prevItem;
+            itemTop = listItem->itemPosition();
+            itemSize = listItem->itemSize();
+        }
+
         // Middle of item and spacing (i.e. the middle of the distance between this item and the next
-        qreal halfwayToNextItem = itemTop + (item->size()+spacing) / 2;
+        qreal halfwayToNextItem = itemTop + (itemSize+spacing) / 2;
         qreal halfwayToPrevItem = itemTop - (prevItemSize+spacing) / 2;
         if (halfwayToNextItem >= pos && halfwayToPrevItem < pos)
             snapItem = item;
 
-        prevItemSize = item->size();
+        prevItemSize = listItem->itemSize();
+        prevItem = item;
     }
     return snapItem;
 }
@@ -1530,15 +1543,15 @@ void QQuickListViewPrivate::fixup(AxisData &data, qreal minExtent, qreal maxExte
                 pos = isContentFlowReversed() ? - header->position() + highlightRangeStart - size() : header->position() - highlightRangeStart;
             } else {
                 if (isContentFlowReversed())
-                    pos = qMax(qMin(-topItem->position() + highlightRangeStart - size(), -maxExtent), -minExtent);
+                    pos = qMax(qMin(-static_cast<FxListItemSG*>(topItem)->itemPosition() + highlightRangeStart - size(), -maxExtent), -minExtent);
                 else
-                    pos = qMax(qMin(topItem->position() - highlightRangeStart, -maxExtent), -minExtent);
+                    pos = qMax(qMin(static_cast<FxListItemSG*>(topItem)->itemPosition() - highlightRangeStart, -maxExtent), -minExtent);
             }
         } else if (bottomItem && isInBounds) {
             if (isContentFlowReversed())
-                pos = qMax(qMin(-bottomItem->position() + highlightRangeEnd - size(), -maxExtent), -minExtent);
+                pos = qMax(qMin(-static_cast<FxListItemSG*>(bottomItem)->itemPosition() + highlightRangeEnd - size(), -maxExtent), -minExtent);
             else
-                pos = qMax(qMin(bottomItem->position() - highlightRangeEnd, -maxExtent), -minExtent);
+                pos = qMax(qMin(static_cast<FxListItemSG*>(bottomItem)->itemPosition() - highlightRangeEnd, -maxExtent), -minExtent);
         } else {
             QQuickItemViewPrivate::fixup(data, minExtent, maxExtent);
             return;
@@ -1568,7 +1581,10 @@ void QQuickListViewPrivate::fixup(AxisData &data, qreal minExtent, qreal maxExte
         timeline.reset(data.move);
         if (viewPos != position()) {
             if (fixupMode != Immediate) {
-                timeline.move(data.move, -viewPos, QEasingCurve(QEasingCurve::InOutQuad), fixupDuration/2);
+                if (fixupMode == ExtentChanged && data.fixingUp)
+                    timeline.move(data.move, -viewPos, QEasingCurve(QEasingCurve::OutQuad), fixupDuration/2);
+                else
+                    timeline.move(data.move, -viewPos, QEasingCurve(QEasingCurve::InOutQuad), fixupDuration/2);
                 data.fixingUp = true;
             } else {
                 timeline.set(data.move, -viewPos);
diff --git a/tests/auto/quick/qquicklistview/data/sectionSnapping.qml b/tests/auto/quick/qquicklistview/data/sectionSnapping.qml
new file mode 100644
index 0000000000..2583cc0377
--- /dev/null
+++ b/tests/auto/quick/qquicklistview/data/sectionSnapping.qml
@@ -0,0 +1,49 @@
+import QtQuick 2.0
+
+ListView {
+    width: 400
+    height: 400
+    preferredHighlightBegin: 100
+    preferredHighlightEnd: 100
+    highlightRangeMode: ListView.StrictlyEnforceRange
+
+    model: ListModel {
+        ListElement { section: "1" }
+        ListElement { section: "1" }
+        ListElement { section: "1" }
+        ListElement { section: "2" }
+        ListElement { section: "2" }
+        ListElement { section: "2" }
+    }
+
+    delegate: Rectangle {
+        width: parent.width
+        height: 50
+        color: index % 2 ? "lightsteelblue" : "steelblue"
+        Text {
+            anchors.centerIn: parent
+            color: "white"
+            text: model.index
+        }
+    }
+
+    section.property: "section"
+    section.delegate: Rectangle {
+        width: parent.width
+        height: 50
+        color: "green"
+        Text {
+            anchors.centerIn: parent
+            color: "white"
+            text: "section"
+        }
+    }
+
+    highlight: Rectangle {
+        y: 100
+        z: 100
+        width: parent.width
+        height: 50
+        color: "#80FF0000"
+    }
+}
diff --git a/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp b/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp
index 2574eb9c6c..ae02352293 100644
--- a/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp
+++ b/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp
@@ -132,6 +132,8 @@ private slots:
     void sectionPropertyChange();
     void sectionDelegateChange();
     void sectionsItemInsertion();
+    void sectionsSnap_data();
+    void sectionsSnap();
     void cacheBuffer();
     void positionViewAtBeginningEnd();
     void positionViewAtIndex();
@@ -2667,6 +2669,62 @@ void tst_QQuickListView::sectionsItemInsertion()
     }
 }
 
+void tst_QQuickListView::sectionsSnap_data()
+{
+    QTest::addColumn<QQuickListView::SnapMode>("snapMode");
+    QTest::addColumn<QPoint>("point");
+    QTest::addColumn<int>("duration");
+
+    QTest::newRow("drag") << QQuickListView::NoSnap << QPoint(100, 45) << 500;
+    QTest::newRow("flick") << QQuickListView::SnapOneItem << QPoint(100, 75) << 50;
+}
+
+void tst_QQuickListView::sectionsSnap()
+{
+    QFETCH(QQuickListView::SnapMode, snapMode);
+    QFETCH(QPoint, point);
+    QFETCH(int, duration);
+
+    QScopedPointer<QQuickView> window(createView());
+    window->setSource(testFileUrl("sectionSnapping.qml"));
+    window->show();
+    QVERIFY(QTest::qWaitForWindowExposed(window.data()));
+
+    QQuickListView *listview = qobject_cast<QQuickListView*>(window->rootObject());
+    QTRY_VERIFY(listview != nullptr);
+    listview->setSnapMode(snapMode);
+
+    QTRY_COMPARE(QQuickItemPrivate::get(listview)->polishScheduled, false);
+    QTRY_COMPARE(listview->currentIndex(), 0);
+    QCOMPARE(listview->contentY(), qreal(-50));
+
+    // move down
+    flick(window.data(), QPoint(100, 100), point, duration);
+    QTRY_VERIFY(!listview->isMovingVertically());
+    QCOMPARE(listview->contentY(), qreal(0));
+
+    flick(window.data(), QPoint(100, 100), point, duration);
+    QTRY_VERIFY(!listview->isMovingVertically());
+    QCOMPARE(listview->contentY(), qreal(50));
+
+    flick(window.data(), QPoint(100, 100), point, duration);
+    QTRY_VERIFY(!listview->isMovingVertically());
+    QCOMPARE(listview->contentY(), qreal(150));
+
+    // move back up
+    flick(window.data(), point, QPoint(100, 100), duration);
+    QTRY_VERIFY(!listview->isMovingVertically());
+    QCOMPARE(listview->contentY(), qreal(50));
+
+    flick(window.data(), point, QPoint(100, 100), duration);
+    QTRY_VERIFY(!listview->isMovingVertically());
+    QCOMPARE(listview->contentY(), qreal(0));
+
+    flick(window.data(), point, QPoint(100, 100), duration);
+    QTRY_VERIFY(!listview->isMovingVertically());
+    QCOMPARE(listview->contentY(), qreal(-50));
+}
+
 void tst_QQuickListView::currentIndex_delayedItemCreation()
 {
     QFETCH(bool, setCurrentToZero);