Qt 4.3: QLineF Class Reference

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# QLineF Class Reference
[QtCore module]

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

     #include <QLineF>

- List of all members, including inherited members

### Public Types

- enum IntersectType { NoIntersection, UnboundedIntersection, BoundedIntersection }

### Public Functions

- QLineF ()
- QLineF ( const QPointF & p1, const QPointF & p2 )
- QLineF ( qreal x1, qreal y1, qreal x2, qreal y2 )
- QLineF ( const QLine & line )
- QPointF p1 () const
- QPointF p2 () const
- qreal x1 () const
- qreal x2 () const
- qreal y1 () const
- qreal y2 () const
- qreal angle ( const QLineF & line ) const
- qreal dx () const
- qreal dy () const
- IntersectType intersect ( const QLineF & line, QPointF * intersectionPoint ) const
- bool isNull () const
- qreal length () const
- QLineF normalVector () const
- QPointF pointAt ( qreal t ) const
- void setLength ( qreal length )
- QLine toLine () const
- void translate ( const QPointF & offset )
- void translate ( qreal dx, qreal dy )
- QLineF unitVector () const
- bool operator!= ( const QLineF & line ) const
- bool operator== ( const QLineF & line ) const

### Related Non-Members

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

## 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. 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, and QRectF.

## Member Type Documentation

### enum QLineF::IntersectType

Describes the intersection between two lines.

QLineF::UnboundedIntersection | QLineF::BoundedIntersection

Constant | Value | Description
--- | --- | ---
`QLineF::NoIntersection` | `0` | Indicates that the lines do not intersect; i.e. they are parallel.
`QLineF::UnboundedIntersection` | `2` | The two lines intersect, but not within the range defined by their lengths. This will be the case if the lines are not parallel.
`QLineF::BoundedIntersection` | `1` | The two lines intersect with each other within the start and end points of each line.

See also intersect().

## Member Function Documentation

### QLineF::QLineF ()

Constructs a null line.

### QLineF::QLineF ( const QPointF & p1, const QPointF & p2 )

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

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

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

### QLineF::QLineF ( const QLine & line )

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

See also toLine().

### QPointF QLineF::p1 () const

Returns the line's start point.

See also x1(), y1(), and p2().

### QPointF QLineF::p2 () const

Returns the line's end point.

See also x2(), y2(), and p1().

### qreal QLineF::x1 () const

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

See also p1().

### qreal QLineF::x2 () const

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

See also p2().

### qreal QLineF::y1 () const

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

See also p1().

### qreal QLineF::y2 () const

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

See also p2().

### 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 origo (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().

### qreal QLineF::dx () const

Returns the horizontal component of the line's vector.

See also dy() and pointAt().

### qreal QLineF::dy () const

Returns the vertical component of the line's vector.

See also dx() and pointAt().

### 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.

### bool QLineF::isNull () const

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

### qreal QLineF::length () const

Returns the length of the line.

See also setLength().

### QLineF QLineF::normalVector () const

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

See also unitVector().

### QPointF QLineF::pointAt ( qreal t ) const

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() and dy().

### void QLineF::setLength ( qreal length )

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

See also length() and isNull().

### 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.

See also QLineF().

### void QLineF::translate ( const QPointF & offset )

Translates this line by the given offset.

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

This is an overloaded member function, provided for convenience.

Translates this line the distance specified by dx and dy.

### 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().

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

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.

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

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.

## Related Non-Members

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

This is an overloaded member function, provided for convenience.

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

See also Format of the QDataStream Operators.

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

This is an overloaded member function, provided for convenience.

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

See also Format of the QDataStream Operators.