Qt 4.3: QLine Class Reference

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# QLine Class Reference
[QtCore module]

The QLine class provides a two-dimensional vector using integer precision. More...

     #include <QLine>

- List of all members, including inherited members

### Public Functions

- QLine ()
- QLine ( const QPoint & p1, const QPoint & p2 )
- QLine ( int x1, int y1, int x2, int y2 )
- QPoint p1 () const
- QPoint p2 () const
- int x1 () const
- int x2 () const
- int y1 () const
- int y2 () const
- int dx () const
- int dy () const
- bool isNull () const
- void translate ( const QPoint & offset )
- void translate ( int dx, int dy )
- bool operator!= ( const QLine & line ) const
- bool operator== ( const QLine & line ) const

### Related Non-Members

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

## Detailed Description

The QLine class provides a two-dimensional vector using integer precision.

A QLine describes a finite length line (or a line segment) on a two-dimensional surface. The start and end points of the line are specified using integer point accuracy for coordinates. Use the QLineF constructor to retrieve a floating point copy.

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. Use isNull() to determine whether the QLine represents a valid line or a null line.

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

See also QLineF, QPolygon, and QRect.

## Member Function Documentation

### QLine::QLine ()

Constructs a null line.

### QLine::QLine ( const QPoint & p1, const QPoint & p2 )

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

### QLine::QLine ( int x1, int y1, int x2, int y2 )

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

### QPoint QLine::p1 () const

Returns the line's start point.

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

### QPoint QLine::p2 () const

Returns the line's end point.

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

### int QLine::x1 () const

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

See also p1().

### int QLine::x2 () const

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

See also p2().

### int QLine::y1 () const

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

See also p1().

### int QLine::y2 () const

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

See also p2().

### int QLine::dx () const

Returns the horizontal component of the line's vector.

See also dy().

### int QLine::dy () const

Returns the vertical component of the line's vector.

See also dx().

### bool QLine::isNull () const

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

### void QLine::translate ( const QPoint & offset )

Translates this line by the given offset.

### void QLine::translate ( int dx, int dy )

This is an overloaded member function, provided for convenience.

Translates this line the distance specified by dx and dy.

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

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

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

### bool QLine::operator== ( const QLine & 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 QLine & 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, QLine & 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.