QLineF Class Reference

The QLineF class provides a two-dimensional vector using floating point precision. More...

#include <qline.h>

Public Types
enum	IntersectType { NoIntersection, BoundedIntersection, UnboundedIntersection }
	Describes the intersection between two lines. More...

Public Functions
qreal	angle () const
	Returns the angle of the line in degrees. More...
qreal	angle (const QLineF &l) const
	Returns the angle (in degrees) between this line and the given line, taking the direction of the lines into account. More...
qreal	angleTo (const QLineF &l) const
	Returns the angle (in positive degrees) from this line to the given line, taking the direction of the lines into account. More...
qreal	dx () const
	Returns the horizontal component of the line's vector. More...
qreal	dy () const
	Returns the vertical component of the line's vector. More...
IntersectType	intersect (const QLineF &l, QPointF *intersectionPoint) const
	Returns a value indicating whether or not this line intersects with the given line. More...
bool	isNull () const
	Returns true if the line is not set up with valid start and end point; otherwise returns false. More...
qreal	length () const
	Returns the length of the line. More...
QLineF	normalVector () const
	Returns a line that is perpendicular to this line with the same starting point and length. More...
bool	operator!= (const QLineF &d) const
	Returns true if the given line is not the same as this line. More...
bool	operator== (const QLineF &d) const
	Returns true if the given line is the same as this line. More...
QPointF	p1 () const
	Returns the line's start point. More...
QPointF	p2 () const
	Returns the line's end point. More...
QPointF	pointAt (qreal t) const
	Returns the point at the parameterized position specified by t. More...
	QLineF ()
	Constructs a null line. More...
	QLineF (const QPointF &pt1, const QPointF &pt2)
	Constructs a line object that represents the line between p1 and p2. More...
	QLineF (qreal x1, qreal y1, qreal x2, qreal y2)
	Constructs a line object that represents the line between (x1, y1) and (x2, y2). More...
	QLineF (const QLine &line)
	Construct a QLineF object from the given integer-based line. More...
void	setAngle (qreal angle)
	Sets the angle of the line to the given angle (in degrees). More...
void	setLength (qreal len)
	Sets the length of the line to the given length. More...
void	setLine (qreal x1, qreal y1, qreal x2, qreal y2)
	Sets this line to the start in x1, y1 and end in x2, y2. More...
void	setP1 (const QPointF &p1)
	Sets the starting point of this line to p1. More...
void	setP2 (const QPointF &p2)
	Sets the end point of this line to p2. More...
void	setPoints (const QPointF &p1, const QPointF &p2)
	Sets the start point of this line to p1 and the end point of this line to p2. More...
QLine	toLine () const
	Returns an integer based copy of this line. More...
void	translate (const QPointF &p)
	Translates this line by the given offset. More...
void	translate (qreal dx, qreal dy)
	Translates this line the distance specified by dx and dy. More...
QLineF	translated (const QPointF &p) const
	Returns this line translated by the given offset. More...
QLineF	translated (qreal dx, qreal dy) const
	Returns this line translated the distance specified by dx and dy. More...
QLineF	unitVector () const
	Returns the unit vector for this line, i.e a line starting at the same point as this line with a length of 1.0. More...
qreal	x1 () const
	Returns the x-coordinate of the line's start point. More...
qreal	x2 () const
	Returns the x-coordinate of the line's end point. More...
qreal	y1 () const
	Returns the y-coordinate of the line's start point. More...
qreal	y2 () const
	Returns the y-coordinate of the line's end point. More...

Static Public Functions
static QLineF	fromPolar (qreal length, qreal angle)
	Returns a QLineF with the given length and angle. More...

Properties
QPointF	pt1
QPointF	pt2

Related Functions
(Note that these are not member functions.)
QDataStream &	operator<< (QDataStream &stream, const QLineF &line)
	Writes the given line to the given stream and returns a reference to the stream. More...
QDataStream &	operator>> (QDataStream &stream, QLineF &line)
	Reads a line from the given stream into the given line and returns a reference to the stream. More...

Detailed Description

The QLineF class provides a two-dimensional vector using floating point precision.

A QLineF describes a finite length line (or line segment) on a two-dimensional surface. QLineF defines the start and end points of the line using floating point accuracy for coordinates. Use the toLine() function to retrieve an integer based copy of this line.

The positions of the line's start and end points can be retrieved using the p1(), x1(), y1(), p2(), x2(), and y2() functions. The dx() and dy() functions return the horizontal and vertical components of the line, respectively.

The line's length can be retrieved using the length() function, and altered using the setLength() function. Similarly, angle() and setAngle() are respectively used for retrieving and altering the angle of the line. Use the isNull() function to determine whether the QLineF represents a valid line or a null line.

The intersect() function determines the IntersectType for this line and a given line, while the angle() function returns the angle between the lines. In addition, the unitVector() function returns a line that has the same starting point as this line, but with a length of only 1, while the normalVector() function returns a line that is perpendicular to this line with the same starting point and length.

Finally, the line can be translated a given offset using the translate() function, and can be traversed using the pointAt() function.

See also

QLine, QPolygonF, QRectF

Definition at line 212 of file qline.h.

Enumerations

IntersectType

enum QLineF::IntersectType

Describes the intersection between two lines.

QLineF::UnboundedIntersection	QLineF::BoundedIntersection

• NoIntersection Indicates that the lines do not intersect; i.e. they are parallel.

• UnboundedIntersection The two lines intersect, but not within the range defined by their lengths. This will be the case if the lines are not parallel.

intersect() will also return this value if the intersect point is within the start and end point of only one of the lines.

• BoundedIntersection The two lines intersect with each other within the start and end points of each line.

See also

intersect()

Enumerator
NoIntersection
BoundedIntersection
UnboundedIntersection

Definition at line 215 of file qline.h.

{ NoIntersection, BoundedIntersection, UnboundedIntersection };

Constructors and Destructors

QLineF() [1/4]

QLineF::QLineF ( )

inline

Constructs a null line.

Definition at line 280 of file qline.h.

Referenced by fromPolar(), normalVector(), operator>>(), and translated().

{
}

QLineF() [2/4]

QLineF::QLineF ( const QPointF &  pt1, const QPointF &  pt2  )

inline

Constructs a line object that represents the line between p1 and p2.

Definition at line 284 of file qline.h.

    : pt1(apt1), pt2(apt2)
{
}

QLineF() [3/4]

QLineF::QLineF ( qreal  x1, qreal  y1, qreal  x2, qreal  y2  )

inline

Constructs a line object that represents the line between (x1, y1) and (x2, y2).

Definition at line 289 of file qline.h.

    : pt1(x1pos, y1pos), pt2(x2pos, y2pos)
{
}

QLineF() [4/4]

QLineF::QLineF ( const QLine &  line )

inline

Construct a QLineF object from the given integer-based line.

See also

toLine()

Definition at line 220 of file qline.h.

: pt1(line.p1()), pt2(line.p2()) { }

Functions

angle() [1/2]

qreal QLineF::angle

(

)

const

Returns the angle of the line in degrees.

Since

4.4

The return value will be in the range of values from 0.0 up to but not including 360.0. The angles are measured counter-clockwise from a point on the x-axis to the right of the origin (x > 0).

See also

setAngle()

Definition at line 719 of file qline.cpp.

Referenced by adapted_angle_on_x(), QPainterPath::angleAtPercent(), angleTo(), and QDeclarativePinchArea::updatePinch().

{
    const qreal dx = pt2.x() - pt1.x();
    const qreal dy = pt2.y() - pt1.y();

    const qreal theta = q_rad2deg(qAtan2(-dy, dx));

    const qreal theta_normalized = theta < 0 ? theta + 360 : theta;

    if (qFuzzyCompare(theta_normalized, qreal(360)))
        return qreal(0);
    else
        return theta_normalized;
}

angle() [2/2]

qreal QLineF::angle

(

const QLineF &

line

)

const

Returns the angle (in degrees) between this line and the given 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 origin (see QLineF::UnboundedIntersection).

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

See also

intersect()

Definition at line 993 of file qline.cpp.

{
    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 >= qreal(-1.0) && cos_line <= qreal(1.0)) rad = qAcos( cos_line );
    return q_rad2deg(rad);
}

angleTo()

qreal QLineF::angleTo

(

const QLineF &

line

)

const

Returns the angle (in positive degrees) from this line to the given line, taking the direction of the lines into account.

Since

4.4

If the lines do not intersect within their range, it is the intersection point of the extended lines that serves as origin (see QLineF::UnboundedIntersection).

The returned value represents the number of degrees you need to add to this line to make it have the same angle as the given line, going counter-clockwise.

See also

intersect()

Definition at line 951 of file qline.cpp.

{
    if (isNull() || l.isNull())
        return 0;

    const qreal a1 = angle();
    const qreal a2 = l.angle();

    const qreal delta = a2 - a1;
    const qreal delta_normalized = delta < 0 ? delta + 360 : delta;

    if (qFuzzyCompare(delta, qreal(360)))
        return 0;
    else
        return delta_normalized;
}

dx()

qreal QLineF::dx ( ) const

inline

Returns the horizontal component of the line's vector.

Return value is positive if x2() >= x1() and negative if x2() < x1().

See also

dy(), pointAt()

Definition at line 324 of file qline.h.

Referenced by angle(), QStroker::joinPoints(), QBezier::midTangent(), normalVector(), qt_stroke_side(), setAngle(), and setLength().

{
    return pt2.x() - pt1.x();
}

dy()

qreal QLineF::dy ( ) const

inline

Returns the vertical component of the line's vector.

Return value is positive if y2() >= y1() and negative if y2() < y1().

See also

dx(), pointAt()

Definition at line 329 of file qline.h.

Referenced by adapted_angle_on_x(), angle(), QStroker::joinPoints(), QBezier::midTangent(), normalVector(), qt_stroke_side(), setAngle(), and setLength().

{
    return pt2.y() - pt1.y();
}

fromPolar()

QLineF QLineF::fromPolar ( qreal  length, qreal  angle  )

static

Returns a QLineF with the given length and angle.

Since

4.4

The first point of the line will be on the origin.

Positive values for the angles mean counter-clockwise while negative values mean the clockwise direction. Zero degrees is at the 3 o'clock position.

Definition at line 774 of file qline.cpp.

{
    const qreal angleR = q_deg2rad(angle);
    return QLineF(0, 0, qCos(angleR) * length, -qSin(angleR) * length);
}

intersect()

QLineF::IntersectType QLineF::intersect	(	const QLineF &	line,
		QPointF *	intersectionPoint
	)		const

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

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

Definition at line 813 of file qline.cpp.

Referenced by QStroker::joinPoints().

{
    // ipmlementation is based on Graphics Gems III's "Faster Line Segment Intersection"
    const QPointF a = pt2 - pt1;
    const QPointF b = l.pt1 - l.pt2;
    const QPointF c = pt1 - l.pt1;

    const qreal denominator = a.y() * b.x() - a.x() * b.y();
    if (denominator == 0 || !qt_is_finite(denominator))
        return NoIntersection;

    const qreal reciprocal = 1 / denominator;
    const qreal na = (b.y() * c.x() - b.x() * c.y()) * reciprocal;
    if (intersectionPoint)
        *intersectionPoint = pt1 + a * na;

    if (na < 0 || na > 1)
        return UnboundedIntersection;

    const qreal nb = (a.x() * c.y() - a.y() * c.x()) * reciprocal;
    if (nb < 0 || nb > 1)
        return UnboundedIntersection;

    return BoundedIntersection;
}

isNull()

bool QLineF::isNull

(

)

const

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

Definition at line 517 of file qline.cpp.

Referenced by angle(), angleTo(), QBezier::endTangent(), setLength(), and QBezier::startTangent().

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

length()

qreal QLineF::length

(

)

const

Returns the length of the line.

See also

setLength()

Definition at line 698 of file qline.cpp.

Referenced by QBezier::addIfClose(), angle(), bezierAtT(), QStroker::joinPoints(), nextBezier(), QPainterPath::percentAtLength(), qt_radial_gradient_adapt_focal_point(), QRasterPaintEnginePrivate::rasterizeLine_dashed(), setAngle(), QRasterPaintEngine::stroke(), and unitVector().

{
    qreal x = pt2.x() - pt1.x();
    qreal y = pt2.y() - pt1.y();
    return qSqrt(x*x + y*y);
}

normalVector()

QLineF QLineF::normalVector ( ) const

inline

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

See also

unitVector()

Definition at line 334 of file qline.h.

Referenced by qt_stroke_side(), and shift().

{
    return QLineF(p1(), p1() + QPointF(dy(), -dx()));
}

operator!=()

bool QLineF::operator!= ( const QLineF &  line ) const

inline

Returns true if the given line is not the same as 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.

Definition at line 267 of file qline.h.

{ return !(*this == d); }

operator==()

bool QLineF::operator== ( const QLineF &  line ) const

inline

Returns true if the given 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.

Definition at line 404 of file qline.h.

{
    return pt1 == d.pt1 && pt2 == d.pt2;
}

p1()

QPointF QLineF::p1 ( ) const

inline

Returns the line's start point.

See also

x1(), y1(), p2()

Definition at line 314 of file qline.h.

Referenced by _q_interpolate(), QPathSegments::addPath(), QCoreGraphicsPaintEngine::drawLines(), QVGPaintEngine::drawLines(), QOpenGLPaintEngine::drawLines(), QPaintEngine::drawLines(), QRasterPaintEngine::drawLines(), QIntersectionFinder::hasIntersections(), QStroker::joinPoints(), QIntersectionFinder::linesIntersect(), QMatrix::map(), normalVector(), operator<<(), operator<<(), qt_stroke_side(), QRasterPaintEnginePrivate::rasterizeLine_dashed(), QRasterPaintEngine::stroke(), and unitVector().

{
    return pt1;
}

p2()

QPointF QLineF::p2 ( ) const

inline

Returns the line's end point.

See also

x2(), y2(), p1()

Definition at line 319 of file qline.h.

Referenced by _q_interpolate(), QPathSegments::addPath(), QCoreGraphicsPaintEngine::drawLines(), QVGPaintEngine::drawLines(), QOpenGLPaintEngine::drawLines(), QPaintEngine::drawLines(), QRasterPaintEngine::drawLines(), QIntersectionFinder::hasIntersections(), QStroker::joinPoints(), QIntersectionFinder::linesIntersect(), QMatrix::map(), operator<<(), operator<<(), qt_radial_gradient_adapt_focal_point(), qt_stroke_side(), QRasterPaintEnginePrivate::rasterizeLine_dashed(), shift(), and QRasterPaintEngine::stroke().

{
    return pt2;
}

pointAt()

QPointF QLineF::pointAt ( qreal  t ) const

inline

Returns the point at the parameterized position specified by t.

The function returns the line's start point if t = 0, and its end point if t = 1.

See also

dx(), dy()

Definition at line 368 of file qline.h.

{
    qreal vx = pt2.x() - pt1.x();
    qreal vy = pt2.y() - pt1.y();
    return QPointF(pt1.x() + vx * t, pt1.y() + vy * t);
}

setAngle()

void QLineF::setAngle

(

qreal

angle

)

Sets the angle of the line to the given angle (in degrees).

Since

4.4

This will change the position of the second point of the line such that the line has the given angle.

Positive values for the angles mean counter-clockwise while negative values mean the clockwise direction. Zero degrees is at the 3 o'clock position.

See also

angle()

Definition at line 749 of file qline.cpp.

{
    const qreal angleR = q_deg2rad(angle);
    const qreal l = length();

    const qreal dx = qCos(angleR) * l;
    const qreal dy = -qSin(angleR) * l;

    pt2.rx() = pt1.x() + dx;
    pt2.ry() = pt1.y() + dy;
}

setLength()

void QLineF::setLength ( qreal  length )

inline

Sets the length of the line to the given length.

QLineF will move the end point - p2() - of the line to give the line its new length. If the given length is negative the angle() is also changed.

If the line is a null line, the length will remain zero regardless of the length specified.

See also

length(), isNull()

Definition at line 360 of file qline.h.

Referenced by QStroker::joinPoints(), qt_radial_gradient_adapt_focal_point(), qt_stroke_side(), and QRasterPaintEnginePrivate::rasterizeLine_dashed().

{
    if (isNull())
        return;
    QLineF v = unitVector();
    pt2 = QPointF(pt1.x() + v.dx() * len, pt1.y() + v.dy() * len);
}

setLine()

void QLineF::setLine ( qreal  x1, qreal  y1, qreal  x2, qreal  y2  )

inline

Sets this line to the start in x1, y1 and end in x2, y2.

Since

4.4

See also

setP1(), setP2(), p1(), p2()

Definition at line 397 of file qline.h.

{
    pt1 = QPointF(aX1, aY1);
    pt2 = QPointF(aX2, aY2);
}

setP1()

void QLineF::setP1 ( const QPointF &  p1 )

inline

Sets the starting point of this line to p1.

Since

4.4

See also

setP2(), p1()

Definition at line 381 of file qline.h.

Referenced by QRasterPaintEnginePrivate::rasterizeLine_dashed().

{
    pt1 = aP1;
}

setP2()

void QLineF::setP2 ( const QPointF &  p2 )

inline

Sets the end point of this line to p2.

Since

4.4

See also

setP1(), p2()

Definition at line 386 of file qline.h.

{
    pt2 = aP2;
}

setPoints()

void QLineF::setPoints ( const QPointF &  p1, const QPointF &  p2  )

inline

Sets the start point of this line to p1 and the end point of this line to p2.

Since

4.4

See also

setP1(), setP2(), p1(), p2()

Definition at line 391 of file qline.h.

{
    pt1 = aP1;
    pt2 = aP2;
}

toLine()

QLine QLineF::toLine ( ) const

inline

Returns an integer based copy of this line.

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

See also

QLineF()

Definition at line 375 of file qline.h.

{
    return QLine(pt1.toPoint(), pt2.toPoint());
}

translate() [1/2]

void QLineF::translate ( const QPointF &  p )

inline

Translates this line by the given offset.

Definition at line 339 of file qline.h.

Referenced by QPainter::drawLines(), drawTextItemDecoration(), QStroker::joinPoints(), qt_stroke_side(), and translate().

{
    pt1 += point;
    pt2 += point;
}

translate() [2/2]

void QLineF::translate ( qreal  dx, qreal  dy  )

inline

Translates this line the distance specified by dx and dy.

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Definition at line 345 of file qline.h.

{
    this->translate(QPointF(adx, ady));
}

translated() [1/2]

QLineF QLineF::translated ( const QPointF &  offset ) const

inline

Returns this line translated by the given offset.

Since

4.4

Definition at line 350 of file qline.h.

Referenced by translated().

{
    return QLineF(pt1 + p, pt2 + p);
}

translated() [2/2]

QLineF QLineF::translated ( qreal  dx, qreal  dy  ) const

inline

Returns this line translated the distance specified by dx and dy.

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Since

4.4

Definition at line 355 of file qline.h.

{
    return translated(QPointF(adx, ady));
}

unitVector()

QLineF QLineF::unitVector

(

)

const

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

See also

normalVector()

Definition at line 786 of file qline.cpp.

Referenced by setLength(), and shift().

{
    qreal x = pt2.x() - pt1.x();
    qreal y = pt2.y() - pt1.y();

    qreal len = qSqrt(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;
}

x1()

qreal QLineF::x1 ( ) const

inline

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

See also

p1()

Definition at line 294 of file qline.h.

Referenced by clipLine(), QX11PaintEngine::drawLines(), QVGPaintEngine::drawLines(), QOpenGLPaintEngine::drawLines(), QStroker::joinPoints(), QTransform::map(), and qt_stroke_side().

{
    return pt1.x();
}

x2()

qreal QLineF::x2 ( ) const

inline

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

See also

p2()

Definition at line 304 of file qline.h.

Referenced by clipLine(), QX11PaintEngine::drawLines(), QVGPaintEngine::drawLines(), QOpenGLPaintEngine::drawLines(), QStroker::joinPoints(), QTransform::map(), and qt_stroke_side().

{
    return pt2.x();
}

y1()

qreal QLineF::y1 ( ) const

inline

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

See also

p1()

Definition at line 299 of file qline.h.

Referenced by clipLine(), QX11PaintEngine::drawLines(), QVGPaintEngine::drawLines(), QOpenGLPaintEngine::drawLines(), QStroker::joinPoints(), QTransform::map(), and qt_stroke_side().

{
    return pt1.y();
}

y2()

qreal QLineF::y2 ( ) const

inline

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

See also

p2()

Definition at line 309 of file qline.h.

Referenced by clipLine(), QX11PaintEngine::drawLines(), QVGPaintEngine::drawLines(), QOpenGLPaintEngine::drawLines(), QStroker::joinPoints(), QTransform::map(), and qt_stroke_side().

{
    return pt2.y();
}

Friends and Related Functions

operator<<()

QDataStream & operator<< ( QDataStream &  stream, const QLineF &  line  )

related

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

See also

{Serializing Qt Data Types}

Definition at line 1026 of file qline.cpp.

Referenced by operator==().

{
    stream << line.p1() << line.p2();
    return stream;
}

operator>>()

QDataStream & operator>> ( QDataStream &  stream, QLineF &  line  )

related

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

See also

{Serializing Qt Data Types}

Definition at line 1044 of file qline.cpp.

Referenced by operator==().

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

    return stream;
}

Properties

pt1

QPointF QLineF::pt1

private

Definition at line 272 of file qline.h.

Referenced by angle(), dx(), dy(), intersect(), isNull(), length(), operator==(), p1(), pointAt(), setAngle(), setLength(), setLine(), setP1(), setPoints(), toLine(), translate(), translated(), unitVector(), x1(), and y1().

pt2

QPointF QLineF::pt2

private

Definition at line 272 of file qline.h.

Referenced by angle(), dx(), dy(), intersect(), isNull(), length(), operator==(), p2(), pointAt(), setAngle(), setLength(), setLine(), setP2(), setPoints(), toLine(), translate(), translated(), unitVector(), x2(), and y2().

---

The documentation for this class was generated from the following files:

• /src/corelib/tools/qline.h
• /src/corelib/tools/qline.cpp