Add QLineF::center() returning the point in the center of the line

[ChangeLog][QtCore][QLine/QLineF] Added center().

Change-Id: I6dcfa9e839190c0a4caf36fb6ecd01b37d65d274
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

src/corelib/tools/qline.cpp

@@ -214,6 +214,14 @@ QT_BEGIN_NAMESPACE
     Returns this line translated the distance specified by \a dx and \a dy.
 */
 
+/*!
+    \fn QPoint QLine::center() const
+
+    \since 5.8
+
+    Returns the center point of this line. This is equivalent to
+    (p1() + p2()) / 2, except it will never overflow.
+*/
 
 /*!
     \fn void QLine::setP1(const QPoint &p1)
@@ -351,6 +359,12 @@ QDataStream &operator>>(QDataStream &stream, QLine &line)
     translate() function, and can be traversed using the pointAt()
     function.
 
+    \section1 Constraints
+
+    QLine is limited to the minimum and maximum values for the
+    \c int type. Operations on a QLine that could potentially result
+    in values outside this range will result in undefined behavior.
+
     \sa QLine, QPolygonF, QRectF
 */
 
@@ -710,6 +724,15 @@ QLineF::IntersectType QLineF::intersect(const QLineF &l, QPointF *intersectionPo
     Returns this line translated the distance specified by \a dx and \a dy.
 */
 
+/*!
+    \fn QPointF QLineF::center() const
+
+    \since 5.8
+
+    Returns the center point of this line. This is equivalent to
+    0.5 * p1() + 0.5 * p2().
+*/
+
 /*!
     \fn void QLineF::setP1(const QPointF &p1)
     \since 4.4

src/corelib/tools/qline.h

@@ -76,6 +76,8 @@ public:
     Q_DECL_CONSTEXPR inline QLine translated(const QPoint &p) const Q_REQUIRED_RESULT;
     Q_DECL_CONSTEXPR inline QLine translated(int dx, int dy) const Q_REQUIRED_RESULT;
 
+    Q_DECL_CONSTEXPR inline QPoint center() const Q_REQUIRED_RESULT;
+
     inline void setP1(const QPoint &p1);
     inline void setP2(const QPoint &p2);
     inline void setPoints(const QPoint &p1, const QPoint &p2);
@@ -165,6 +167,11 @@ Q_DECL_CONSTEXPR inline QLine QLine::translated(int adx, int ady) const
     return translated(QPoint(adx, ady));
 }
 
+Q_DECL_CONSTEXPR inline QPoint QLine::center() const
+{
+    return QPoint(int((qint64(pt1.x()) + pt2.x()) / 2), int((qint64(pt1.y()) + pt2.y()) / 2));
+}
+
 inline void QLine::setP1(const QPoint &aP1)
 {
     pt1 = aP1;
@@ -253,6 +260,8 @@ public:
     Q_DECL_CONSTEXPR inline QLineF translated(const QPointF &p) const Q_REQUIRED_RESULT;
     Q_DECL_CONSTEXPR inline QLineF translated(qreal dx, qreal dy) const Q_REQUIRED_RESULT;
 
+    Q_DECL_CONSTEXPR inline QPointF center() const Q_REQUIRED_RESULT;
+
     inline void setP1(const QPointF &p1);
     inline void setP2(const QPointF &p2);
     inline void setPoints(const QPointF &p1, const QPointF &p2);
@@ -357,6 +366,11 @@ Q_DECL_CONSTEXPR inline QLineF QLineF::translated(qreal adx, qreal ady) const
     return translated(QPointF(adx, ady));
 }
 
+Q_DECL_CONSTEXPR inline QPointF QLineF::center() const
+{
+    return QPointF(0.5 * pt1.x() + 0.5 * pt2.x(), 0.5 * pt1.y() + 0.5 * pt2.y());
+}
+
 inline void QLineF::setLength(qreal len)
 {
     if (isNull())

tests/auto/corelib/tools/qline/tst_qline.cpp

@@ -44,6 +44,12 @@ private slots:
     void testLength();
     void testLength_data();
 
+    void testCenter();
+    void testCenter_data();
+
+    void testCenterF();
+    void testCenterF_data();
+
     void testNormalVector();
     void testNormalVector_data();
 
@@ -268,6 +274,77 @@ void tst_QLine::testLength()
     QCOMPARE(l.dy(), qreal(vy));
 }
 
+void tst_QLine::testCenter()
+{
+    QFETCH(int, x1);
+    QFETCH(int, y1);
+    QFETCH(int, x2);
+    QFETCH(int, y2);
+    QFETCH(int, centerX);
+    QFETCH(int, centerY);
+
+    const QPoint c = QLine(x1, y1, x2, y2).center();
+    QCOMPARE(centerX, c.x());
+    QCOMPARE(centerY, c.y());
+}
+
+void tst_QLine::testCenter_data()
+{
+    QTest::addColumn<int>("x1");
+    QTest::addColumn<int>("y1");
+    QTest::addColumn<int>("x2");
+    QTest::addColumn<int>("y2");
+    QTest::addColumn<int>("centerX");
+    QTest::addColumn<int>("centerY");
+
+    QTest::newRow("[0, 0]") << 0 << 0 << 0 << 0 << 0 << 0;
+    QTest::newRow("top") << 0 << 0 << 2 << 0 << 1 << 0;
+    QTest::newRow("right") << 0 << 0 << 0 << 2 << 0 << 1;
+    QTest::newRow("bottom") << 0 << 0 << -2 << 0 << -1 << 0;
+    QTest::newRow("left") << 0 << 0 << 0 << -2 << 0 << -1;
+
+    QTest::newRow("precision+") << 0 << 0 << 1 << 1 << 0 << 0;
+    QTest::newRow("precision-") << -1 << -1 << 0 << 0 << 0 << 0;
+
+    const int max = std::numeric_limits<int>::max();
+    const int min = std::numeric_limits<int>::min();
+    QTest::newRow("max") << max << max << max << max << max << max;
+    QTest::newRow("min") << min << min << min << min << min << min;
+    QTest::newRow("minmax") << min << min << max << max << 0 << 0;
+}
+
+void tst_QLine::testCenterF()
+{
+    QFETCH(double, x1);
+    QFETCH(double, y1);
+    QFETCH(double, x2);
+    QFETCH(double, y2);
+    QFETCH(double, centerX);
+    QFETCH(double, centerY);
+
+    const QPointF c = QLineF(x1, y1, x2, y2).center();
+    QCOMPARE(centerX, c.x());
+    QCOMPARE(centerY, c.y());
+}
+
+void tst_QLine::testCenterF_data()
+{
+    QTest::addColumn<double>("x1");
+    QTest::addColumn<double>("y1");
+    QTest::addColumn<double>("x2");
+    QTest::addColumn<double>("y2");
+    QTest::addColumn<double>("centerX");
+    QTest::addColumn<double>("centerY");
+
+    QTest::newRow("[0, 0]") << 0.0 << 0.0 << 0.0 << 0.0 << 0.0 << 0.0;
+    QTest::newRow("top") << 0.0 << 0.0 << 1.0 << 0.0 << 0.5 << 0.0;
+    QTest::newRow("right") << 0.0 << 0.0 << 0.0 << 1.0 << 0.0 << 0.5;
+    QTest::newRow("bottom") << 0.0 << 0.0 << -1.0 << 0.0 << -0.5 << 0.0;
+    QTest::newRow("left") << 0.0 << 0.0 << 0.0 << -1.0 << 0.0 << -0.5;
+
+    const double max = std::numeric_limits<qreal>::max();
+    QTest::newRow("max") << max << max << max << max << max << max;
+}
 
 void tst_QLine::testNormalVector_data()
 {