ListView: fix rounding errors

Task-number: QTBUG-37339
Change-Id: I223e4d6bcabb1daa705c0ed2212e7e2b2fc3f37c
Reviewed-by: Andy Shaw <andy.shaw@digia.com>
Reviewed-by: Alan Alpert <aalpert@blackberry.com>

2 files changed, 190 insertions, 0 deletions

diff --git a/tests/auto/quick/qquicklistview/data/roundingErrors.qml b/tests/auto/quick/qquicklistview/data/roundingErrors.qml
new file mode 100644
index 0000000000..aebdce04c3
--- /dev/null
+++ b/tests/auto/quick/qquicklistview/data/roundingErrors.qml
@@ -0,0 +1,130 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** You may use this file under the terms of the BSD license as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of Digia Plc and its Subsidiary(-ies) nor the names
+**     of its contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+import QtQuick 2.0
+import QtQml.Models 2.1
+
+ListView {
+    id: listview
+
+    width: 600
+    height: 200
+
+    spacing: 8
+    orientation: ListView.Horizontal
+
+    Component.onCompleted: {
+        var colors = ["blue", "green", "red", "yellow", "orange", "purple", "cyan",
+                      "magenta", "chartreuse", "aquamarine", "indigo", "lightsteelblue",
+                      "violet", "grey", "springgreen", "salmon", "blanchedalmond",
+                      "forestgreen", "pink", "navy", "goldenrod", "crimson", "teal" ]
+        for (var i = 0; i < 100; ++i)
+            colorModel.append( { nid: i,  color: colors[i%colors.length] } )
+    }
+
+    model: DelegateModel {
+        id: visualModel
+
+        model: ListModel {
+            id: colorModel
+        }
+
+        delegate: MouseArea {
+            id: delegateRoot
+            objectName: model.nid
+
+            width: 107.35
+            height: 63.35
+
+            drag.target: icon
+
+            Rectangle{
+                id: icon
+                width: delegateRoot.width
+                height: delegateRoot.height
+                anchors.horizontalCenter: parent.horizontalCenter
+                anchors.verticalCenter: parent.verticalCenter
+                color: model.color
+
+                Drag.active: delegateRoot.drag.active
+                Drag.source: delegateRoot
+                Drag.hotSpot.x: 36
+                Drag.hotSpot.y: 36
+
+                Text {
+                    id: text
+                    anchors.fill: parent
+                    font.pointSize: 40
+                    text: model.nid
+                    horizontalAlignment: Qt.AlignHCenter
+                    verticalAlignment: Qt.AlignVCenter
+                }
+
+                states: [
+                    State {
+                        when: icon.Drag.active
+                        ParentChange {
+                            target: icon
+                            parent: delegateRoot.ListView.view
+                        }
+
+                        AnchorChanges {
+                            target: icon
+                            anchors.horizontalCenter: undefined
+                            anchors.verticalCenter: undefined
+                        }
+                    }
+                ]
+            }
+        }
+    }
+
+    DropArea {
+        anchors.fill: parent
+        onPositionChanged: {
+            var to = listview.indexAt(drag.x + listview.contentX, 0)
+            if (to !== -1) {
+                var from = drag.source.DelegateModel.itemsIndex
+                if (from !== to)
+                    visualModel.items.move(from, to)
+                drag.accept()
+            }
+        }
+    }
+}
diff --git a/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp b/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp
index 288c0d0a58..29755e3890 100644
--- a/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp
+++ b/tests/auto/quick/qquicklistview/tst_qquicklistview.cpp
@@ -224,6 +224,9 @@ private slots:
     void QTBUG_36481();
     void QTBUG_35920();
 
+    void roundingErrors();
+    void roundingErrors_data();
+
 private:
     template <class T> void items(const QUrl &source);
     template <class T> void changed(const QUrl &source);
@@ -7201,6 +7204,63 @@ void tst_QQuickListView::QTBUG_35920()
     QTest::mouseRelease(window.data(), Qt::LeftButton, 0, QPoint(10,100));
 }
 
+void tst_QQuickListView::roundingErrors()
+{
+    QFETCH(bool, pixelAligned);
+
+    QScopedPointer<QQuickView> window(createView());
+    window->setSource(testFileUrl("roundingErrors.qml"));
+    window->show();
+    QVERIFY(QTest::qWaitForWindowExposed(window.data()));
+
+    QQuickListView *listview = qobject_cast<QQuickListView *>(window->rootObject());
+    QVERIFY(listview);
+    listview->setPixelAligned(pixelAligned);
+    listview->positionViewAtIndex(20, QQuickListView::Beginning);
+
+    QQuickItem *content = listview->contentItem();
+    QVERIFY(content);
+
+    const QPoint viewPos(150, 36);
+    const QPointF contentPos = content->mapFromItem(listview, viewPos);
+
+    QPointer<QQuickItem> item = listview->itemAt(contentPos.x(), contentPos.y());
+    QVERIFY(item);
+
+    // QTBUG-37339: drag an item and verify that it doesn't
+    // get prematurely released due to rounding errors
+    QTest::mousePress(window.data(), Qt::LeftButton, 0, viewPos);
+    for (int i = 0; i < 150; i += 5) {
+        QTest::mouseMove(window.data(), viewPos - QPoint(i, 0));
+        QVERIFY(item);
+    }
+    QTest::mouseRelease(window.data(), Qt::LeftButton, 0, QPoint(0, 36));
+
+    // maintain position relative to the right edge
+    listview->setLayoutDirection(Qt::RightToLeft);
+    const qreal contentX = listview->contentX();
+    listview->setContentX(contentX + 0.2);
+    QCOMPARE(listview->contentX(), pixelAligned ? qRound(contentX + 0.2) : contentX + 0.2);
+    listview->setWidth(listview->width() - 0.2);
+    QCOMPARE(listview->contentX(), pixelAligned ? qRound(contentX + 0.2) : contentX + 0.2);
+
+    // maintain position relative to the bottom edge
+    listview->setOrientation(QQuickListView::Vertical);
+    listview->setVerticalLayoutDirection(QQuickListView::BottomToTop);
+    const qreal contentY = listview->contentY();
+    listview->setContentY(contentY + 0.2);
+    QCOMPARE(listview->contentY(), pixelAligned ? qRound(contentY + 0.2) : contentY + 0.2);
+    listview->setHeight(listview->height() - 0.2);
+    QCOMPARE(listview->contentY(), pixelAligned ? qRound(contentY + 0.2) : contentY + 0.2);
+}
+
+void tst_QQuickListView::roundingErrors_data()
+{
+    QTest::addColumn<bool>("pixelAligned");
+    QTest::newRow("pixelAligned=true") << true;
+    QTest::newRow("pixelAligned=false") << false;
+}
+
 QTEST_MAIN(tst_QQuickListView)
 
 #include "tst_qquicklistview.moc"