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QPoint Class Reference[QtCore module]

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

` #include <QPoint>`

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.

Member Function Documentation

QPoint::QPoint ()

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

QPoint::QPoint ( int x, int y )

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

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)```

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)```

void QPoint::setX ( int x )

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

void QPoint::setY ( int y )

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

int QPoint::x () const

Returns the x coordinate of this point.

int QPoint::y () const

Returns the y coordinate of this point.

QPoint & QPoint::operator*= ( qrealfactor )

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.

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)```

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)```

QPoint & QPoint::operator/= ( qrealdivisor )

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.

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, qrealfactor )

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.

const QPoint operator* ( qrealfactor, const QPoint & point )

This is an overloaded member function, provided for convenience.

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.

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.

const QPoint operator- ( const QPoint & point )

This is an overloaded member function, provided for convenience.

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, qrealdivisor )

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.

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

This is an overloaded member function, provided for convenience.

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

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 )

This is an overloaded member function, provided for convenience.

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