Qt 4.7: QPoint Class Reference

Qt Reference Documentation

# QPoint Class Reference

The QPoint class defines a point in the plane using integer precision. More...

     #include <QPoint>

- List of all members, including inherited members

## Public Functions

| QPoint ()
| QPoint ( int x, int y )
bool | isNull () const
int | manhattanLength () const
int & | rx ()
int & | ry ()
void | setX ( int x )
void | setY ( int y )
int | x () const
int | y () const
QPoint & | operator*= ( qreal factor )
QPoint & | operator+= ( const QPoint & point )
QPoint & | operator-= ( const QPoint & point )
QPoint & | operator/= ( qreal divisor )

## Related Non-Members

bool | operator!= ( const QPoint & p1, const QPoint & p2 )
const QPoint | operator* ( const QPoint & point, qreal factor )
const QPoint | operator* ( qreal factor, const QPoint & point )
const QPoint | operator+ ( const QPoint & p1, const QPoint & p2 )
const QPoint | operator- ( const QPoint & p1, const QPoint & p2 )
const QPoint | operator- ( const QPoint & point )
const QPoint | operator/ ( const QPoint & point, qreal divisor )
QDataStream & | operator<< ( QDataStream & stream, const QPoint & point )
bool | operator== ( const QPoint & p1, const QPoint & p2 )
QDataStream & | operator>> ( QDataStream & stream, QPoint & point )

## Detailed Description

The QPoint class defines a point in the plane using integer precision.

A point is specified by a x coordinate and an y coordinate which can be accessed using the x() and y() functions. The isNull() function returns true if both x and y are set to 0. The coordinates can be set (or altered) using the setX() and setY() functions, or alternatively the rx() and ry() functions which return references to the coordinates (allowing direct manipulation).

Given a point p, the following statements are all equivalent:

     QPoint p;

     p.setX(p.x() + 1);
     p += QPoint(1, 0);
     p.rx()++;

A QPoint object can also be used as a vector: Addition and subtraction are defined as for vectors (each component is added separately). A QPoint object can also be divided or multiplied by an `int` or a `qreal`.

In addition, the QPoint class provides the manhattanLength() function which gives an inexpensive approximation of the length of the QPoint object interpreted as a vector. Finally, QPoint objects can be streamed as well as compared.

See also QPointF and QPolygon.

## Member Function Documentation

### QPoint::QPoint ()

Constructs a null point, i.e. with coordinates (0, 0)

See also isNull().

### QPoint::QPoint ( int x, int y )

Constructs a point with the given coordinates (x, y).

See also setX() and setY().

### bool QPoint::isNull () const

Returns true if both the x and y coordinates are set to 0, otherwise returns false.

### int QPoint::manhattanLength () const

Returns the sum of the absolute values of x() and y(), traditionally known as the "Manhattan length" of the vector from the origin to the point. For example:

     QPoint oldPosition;

     MyWidget::mouseMoveEvent(QMouseEvent *event)
     {
         QPoint point = event->pos() - oldPosition;
         if (point.manhattanLength() > 3)
             // the mouse has moved more than 3 pixels since the oldPosition
     }

This is a useful, and quick to calculate, approximation to the true length:

     double trueLength = sqrt(pow(x(), 2) + pow(y(), 2));

The tradition of "Manhattan length" arises because such distances apply to travelers who can only travel on a rectangular grid, like the streets of Manhattan.

### int & QPoint::rx ()

Returns a reference to the x coordinate of this point.

Using a reference makes it possible to directly manipulate x. For example:

     QPoint p(1, 2);
     p.rx()--;   // p becomes (0, 2)

See also x() and setX().

### int & QPoint::ry ()

Returns a reference to the y coordinate of this point.

Using a reference makes it possible to directly manipulate y. For example:

     QPoint p(1, 2);
     p.ry()++;   // p becomes (1, 3)

See also y() and setY().

### void QPoint::setX ( int x )

Sets the x coordinate of this point to the given x coordinate.

See also x() and setY().

### void QPoint::setY ( int y )

Sets the y coordinate of this point to the given y coordinate.

See also y() and setX().

### int QPoint::x () const

Returns the x coordinate of this point.

See also setX() and rx().

### int QPoint::y () const

Returns the y coordinate of this point.

See also setY() and ry().

### QPoint & QPoint::operator*= ( qreal factor )

Multiplies this point's coordinates by the given factor, and returns a reference to this point. For example:

     QPoint p(-1, 4);
     p *= 2.5;    // p becomes (-3, 10)

Note that the result is rounded to the nearest integer as points are held as integers. Use QPointF for floating point accuracy.

See also operator/=().

### QPoint & QPoint::operator+= ( const QPoint & point )

Adds the given point to this point and returns a reference to this point. For example:

     QPoint p( 3, 7);
     QPoint q(-1, 4);
     p += q;    // p becomes (2, 11)

See also operator-=().

### QPoint & QPoint::operator-= ( const QPoint & point )

Subtracts the given point from this point and returns a reference to this point. For example:

     QPoint p( 3, 7);
     QPoint q(-1, 4);
     p -= q;    // p becomes (4, 3)

See also operator+=().

### QPoint & QPoint::operator/= ( qreal divisor )

This is an overloaded function.

Divides both x and y by the given divisor, and returns a reference to this point. For example:

     QPoint p(-3, 10);
     p /= 2.5;           // p becomes (-1, 4)

Note that the result is rounded to the nearest integer as points are held as integers. Use QPointF for floating point accuracy.

See also operator*=().

## Related Non-Members

### bool operator!= ( const QPoint & p1, const QPoint & p2 )

Returns true if p1 and p2 are not equal; otherwise returns false.

### const QPoint operator* ( const QPoint & point, qreal factor )

Returns a copy of the given point multiplied by the given factor.

Note that the result is rounded to the nearest integer as points are held as integers. Use QPointF for floating point accuracy.

See also QPoint::operator*=().

### const QPoint operator* ( qreal factor, const QPoint & point )

This is an overloaded function.

Returns a copy of the given point multiplied by the given factor.

### const QPoint operator+ ( const QPoint & p1, const QPoint & p2 )

Returns a QPoint object that is the sum of the given points, p1 and p2; each component is added separately.

See also QPoint::operator+=().

### const QPoint operator- ( const QPoint & p1, const QPoint & p2 )

Returns a QPoint object that is formed by subtracting p2 from p1; each component is subtracted separately.

See also QPoint::operator-=().

### const QPoint operator- ( const QPoint & point )

This is an overloaded function.

Returns a QPoint object that is formed by changing the sign of both components of the given point.

Equivalent to `QPoint(0,0) - point`.

### const QPoint operator/ ( const QPoint & point, qreal divisor )

Returns the QPoint formed by dividing both components of the given point by the given divisor.

Note that the result is rounded to the nearest integer as points are held as integers. Use QPointF for floating point accuracy.

See also QPoint::operator/=().

### QDataStream & operator<< ( QDataStream & stream, const QPoint & point )

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

See also Serializing Qt Data Types.

### bool operator== ( const QPoint & p1, const QPoint & p2 )

Returns true if p1 and p2 are equal; otherwise returns false.

### QDataStream & operator>> ( QDataStream & stream, QPoint & point )

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

See also Serializing Qt Data Types.