qline.cpp

奇趣公司比较新的qt/emd版本

*/

/*!
    Returns true if the line is not set up with valid start and end point;
    otherwise returns false.
*/

bool QLineF::isNull() const
{
    return (qFuzzyCompare(pt1.x(), pt2.x()) && qFuzzyCompare(pt1.y(), pt2.y())) ? true : false;
}


/*!
    \fn QPointF QLineF::p1() const

    Returns the line's start point.

    \sa x1(), y1(), p2()
*/

/*!
    \fn QPointF QLineF::p2() const

    Returns the line's end point.

    \sa x2(), y2(), p1()
*/

/*!
    \fn QLine QLineF::toLine() const

    Returns an integer based copy of this line.

    Note that the returned line's start and end points are rounded to
    the nearest integer.

    \sa QLineF()
*/
/*!
    \fn qreal QLineF::x1() const

    Returns the x-coordinate of the line's start point.

    \sa p1()
*/

/*!
    \fn qreal QLineF::y1() const

    Returns the y-coordinate of the line's start point.

    \sa p1()
*/

/*!
    \fn qreal QLineF::x2() const

    Returns the x-coordinate of the line's end point.

    \sa p2()
*/

/*!
    \fn qreal QLineF::y2() const

    Returns the y-coordinate of the line's end point.

    \sa p2()
*/

/*!
    \fn qreal QLineF::dx() const

    Returns the horizontal component of the line's vector.

    \sa dy(), pointAt()
*/

/*!
    \fn qreal QLineF::dy() const

    Returns the vertical component of the line's vector.

    \sa dx(), pointAt()
*/

/*!
    \fn QLineF::setLength(qreal length)

    Sets the length of the line to the given \a length. If the line is a
    null line, the length will remain zero regardless of the length
    specified.

    \sa length(), isNull()
*/

/*!
    \fn QLineF QLineF::normalVector() const

    Returns a line that is perpendicular to this line with the same starting
    point and length.

    \image qlinef-normalvector.png

    \sa unitVector()
*/

/*!
    \fn bool QLineF::operator!=(const QLineF &line) const

    Returns true if the given \a line is not the same as \e this line.

    A line is different from another line if their start or end points
    differ, or the internal order of the points is different.
*/

/*!
    \fn bool QLineF::operator==(const QLineF &line) const

    Returns true if the given \a line is the same as this line.

    A line is identical to another line if the start and end points
    are identical, and the internal order of the points is the same.
*/

/*!
  \fn qreal QLineF::pointAt(qreal t) const

  Returns the point at the parameterized position specified by \a
  t. The function returns the line's start point if t = 0, and its end
  point if t = 1.

  \sa dx(), dy()
*/

/*!
    Returns the length of the line.

    \sa setLength()
*/
qreal QLineF::length() const
{
    qreal x = pt2.x() - pt1.x();
    qreal y = pt2.y() - pt1.y();
    return sqrt(x*x + y*y);
}


/*!
    Returns the unit vector for this line, i.e a line starting at the
    same point as \e this line with a length of 1.0.

    \sa normalVector()
*/
QLineF QLineF::unitVector() const
{
    qreal x = pt2.x() - pt1.x();
    qreal y = pt2.y() - pt1.y();

    qreal len = sqrt(x*x + y*y);
    QLineF f(p1(), QPointF(pt1.x() + x/len, pt1.y() + y/len));

#ifndef QT_NO_DEBUG
    if (qAbs(f.length() - 1) >= 0.001)
        qWarning("QLine::unitVector: New line does not have unit length");
#endif

    return f;
}

#define SAME_SIGNS(a, b) ((a) * (b) >= 0)

// Line intersection algorithm, copied from Graphics Gems II
static bool qt_linef_intersect(qreal x1, qreal y1, qreal x2, qreal y2,
                               qreal x3, qreal y3, qreal x4, qreal y4)
{
    qreal a1, a2, b1, b2, c1, c2; /* Coefficients of line eqns. */
    qreal r1, r2, r3, r4;         /* 'Sign' values */

    a1 = y2 - y1;
    b1 = x1 - x2;
    c1 = x2 * y1 - x1 * y2;

    r3 = a1 * x3 + b1 * y3 + c1;
    r4 = a1 * x4 + b1 * y4 + c1;

    if ( r3 != 0 && r4 != 0 && SAME_SIGNS( r3, r4 ))
        return false;

    a2 = y4 - y3;
    b2 = x3 - x4;
    c2 = x4 * y3 - x3 * y4;

    r1 = a2 * x1 + b2 * y1 + c2;
    r2 = a2 * x2 + b2 * y2 + c2;

    if ( r1 != 0 && r2 != 0 && SAME_SIGNS( r1, r2 ))
        return false;

    return true;
}

/*!
    \fn QLineF::IntersectType QLineF::intersect(const QLineF &line, QPointF *intersectionPoint) const

    Returns a value indicating whether or not \e this line intersects
    with the given \a line.

    The actual intersection point is extracted to \a intersectionPoint
    (if the pointer is valid). If the lines are parallel, the
    intersection point is undefined.
*/

QLineF::IntersectType QLineF::intersect(const QLineF &l, QPointF *intersectionPoint) const
{
    if (isNull() || l.isNull()
        || !qt_is_finite(pt1.x()) || !qt_is_finite(pt1.y()) || !qt_is_finite(pt2.x()) || !qt_is_finite(pt2.y())
        || !qt_is_finite(l.pt1.x()) || !qt_is_finite(l.pt1.y()) || !qt_is_finite(l.pt2.x()) || !qt_is_finite(l.pt2.y()))
        return NoIntersection;

    QPointF isect;
    IntersectType type = qt_linef_intersect(pt1.x(), pt1.y(), pt2.x(), pt2.y(),
                                            l.x1(), l.y1(), l.x2(), l.y2())
                         ? BoundedIntersection : UnboundedIntersection;

    bool dx_zero = qFuzzyCompare(dx(), 0);
    bool ldx_zero = qFuzzyCompare(l.dx(), 0);

    // For special case where one of the lines are vertical
    if (dx_zero && ldx_zero) {
        type = NoIntersection;
    } else if (dx_zero) {
        qreal la = l.dy() / l.dx();
        isect = QPointF(pt1.x(), la * pt1.x() + l.y1() - la*l.x1());
    } else if (ldx_zero) {
        qreal ta = dy() / dx();
        isect = QPointF(l.x1(), ta * l.x1() + y1() - ta*x1());
    } else {
        qreal ta = dy()/dx();
        qreal la = l.dy()/l.dx();
        if (ta == la) // no intersection
            return NoIntersection;

        qreal x = ( - l.y1() + la * l.x1() + pt1.y() - ta * pt1.x() ) / (la - ta);
        isect = QPointF(x, ta*(x - pt1.x()) + pt1.y());
    }
    if (intersectionPoint)
        *intersectionPoint = isect;
    return type;
}

/*!
    \fn void QLineF::translate(const QPointF &offset)

    Translates this line by the given \a offset.
*/

/*!
    \fn void QLineF::translate(qreal dx, qreal dy)
    \overload

    Translates this line the distance specified by \a dx and \a dy.
*/

/*!
  \fn qreal QLineF::angle(const QLineF &line) const

  Returns the angle (in degrees) between this line and the given \a
  line, taking the direction of the lines into account. If the lines
  do not intersect within their range, it is the intersection point of
  the extended lines that serves as origo (see
  QLineF::UnboundedIntersection).

  \table
  \row
  \o \inlineimage qlinef-angle-identicaldirection.png
  \o \inlineimage qlinef-angle-oppositedirection.png
  \endtable

  When the lines are parallel, this function returns 0 if they have
  the same direction; otherwise it returns 180.

  \sa intersect()
*/
qreal QLineF::angle(const QLineF &l) const
{
    if (isNull() || l.isNull())
        return 0;
    qreal cos_line = (dx()*l.dx() + dy()*l.dy()) / (length()*l.length());
    qreal rad = 0;
    // only accept cos_line in the range [-1,1], if it is outside, use 0 (we return 0 rather than PI for those cases)
    if (cos_line >= -1.0 && cos_line <= 1.0) rad = acos( cos_line );
    return rad * 360 / M_2PI;
}


#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug d, const QLineF &p)
{
    d << "QLineF(" << p.p1() << "," << p.p2() << ")";
    return d;
}
#endif

#ifndef QT_NO_DATASTREAM
/*!
    \relates QLineF

    Writes the given \a line to the given \a stream and returns a
    reference to the stream.

    \sa {Format of the QDataStream Operators}
*/

QDataStream &operator<<(QDataStream &stream, const QLineF &line)
{
    stream << line.p1() << line.p2();
    return stream;
}

/*!
    \relates QLineF

    Reads a line from the given \a stream into the given \a line and
    returns a reference to the stream.

    \sa {Format of the QDataStream Operators}
*/

QDataStream &operator>>(QDataStream &stream, QLineF &line)
{
    QPointF start, end;
    stream >> start;
    stream >> end;
    line = QLineF(start, end);

    return stream;
}

#endif // QT_NO_DATASTREAM