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QPoint Class Reference

The QPoint class defines a point in the plane. More...

#include <qpoint.h>

List of all member functions.

Public Members

Related Functions

Detailed Description

The QPoint class defines a point in the plane.

A point is specified by an x coordinate and a y coordinate.

The coordinate type is QCOORD (a 32-bit integer). The minimum value of QCOORD is QCOORD_MIN (-2147483648) and the maximum value is QCOORD_MAX (2147483647).

The coordinates are accessed by the functions x() and y(); they can be set by setX() and setY() or by the reference functions rx() and ry().

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

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

A QPoint can also be used as a vector. Addition and subtraction of QPoints are defined as for vectors (each component is added separately). You can divide or multiply a QPoint by an int or a double. The function manhattanLength() gives an inexpensive approximation of the length of the QPoint interpreted as a vector.

Example: 

     //QPoint oldPos is defined somewhere else
     MyWidget::mouseMoveEvent( QMouseEvent *e )
     {
        QPoint vector = e->pos() - oldPos;
        if ( vector.manhattanLength() > 3 )
           ... //mouse has moved more than 3 pixels since oldPos
     }

QPoints can be compared for equality or inequality, and they can be written to and read from a QStream.

See also QSize, QRect, Graphics Classes and Image Processing Classes.

Member Function Documentation

QPoint::QPoint ()

Constructs a point with coordinates (0,0) (isNull() returns TRUE).

QPoint::QPoint ( int xpos, int ypos )

Constructs a point with the x value xpos and y value ypos.

bool QPoint::isNull () const

Returns TRUE if both the x value and the y value are 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. The tradition arises because such distances apply to travelers who can only travel on a rectangular grid, like the streets of Manhattan.

This is a useful, and quick to calculate, approximation to the true length: sqrt(pow(x(),2)+pow(y(),2)).

QPoint & QPoint::operator*= ( int c )

Multiplies both x and y with c, and returns a reference to this point.

Example: 

    QPoint p( -1, 4 );
    p *= 2;                     // p becomes (-2,8)

QPoint & QPoint::operator*= ( double c )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Multiplies both x and y with c, and returns a reference to this point.

Example: 

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

Note that the result is truncated.

QPoint & QPoint::operator+= ( const QPoint & p )

Adds p to the point and returns a reference to this point.

Example: 

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

QPoint & QPoint::operator-= ( const QPoint & p )

Subtracts p from the point and returns a reference to this point.

Example: 

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

QPoint & QPoint::operator/= ( int c )

Divides both x and y by c, and returns a reference to this point.

Example: 

    QPoint p( -2, 8 );
    p /= 2;                     // p becomes (-1,4)

QPoint & QPoint::operator/= ( double c )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Divides both x and y by c, and returns a reference to this point.

Example: 

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

Note that the result is truncated because points are held as integers.

QCOORD & QPoint::rx ()

Returns a reference to the x coordinate of the point.

Using a reference makes it possible to directly manipulate x.

Example: 

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

See also ry().

QCOORD & QPoint::ry ()

Returns a reference to the y coordinate of the point.

Using a reference makes it possible to directly manipulate y.

Example: 

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

See also rx().

void QPoint::setX ( int x )

Sets the x coordinate of the point to x.

See also x() and setY().

Example: t14/cannon.cpp.

void QPoint::setY ( int y )

Sets the y coordinate of the point to y.

See also y() and setX().

Example: t14/cannon.cpp.

int QPoint::x () const

Returns the x coordinate of the point.

See also setX() and y().

Examples: canvas/canvas.cpp, dirview/dirview.cpp, fileiconview/qfileiconview.cpp, life/life.cpp, t14/cannon.cpp and themes/wood.cpp.

int QPoint::y () const

Returns the y coordinate of the point.

See also setY() and x().

Examples: canvas/canvas.cpp, fileiconview/qfileiconview.cpp, life/life.cpp, t14/cannon.cpp and themes/wood.cpp.

Related Functions

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 & p, int c )

Returns the QPoint formed by multiplying both components of p by c.

const QPoint operator* ( int c, const QPoint & p )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the QPoint formed by multiplying both components of p by c.

const QPoint operator* ( const QPoint & p, double c )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the QPoint formed by multiplying both components of p by c.

Note that the result is truncated because points are held as integers.

const QPoint operator* ( double c, const QPoint & p )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the QPoint formed by multiplying both components of p by c.

Note that the result is truncated because points are held as integers.

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

Returns the sum of p1 and p2; each component is added separately.

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

Returns p2 subtracted from p1; each component is subtracted separately.

const QPoint operator- ( const QPoint & p )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the QPoint formed by changing the sign of both components of p, equivalent to QPoint(0,0) - p.

const QPoint operator/ ( const QPoint & p, int c )

Returns the QPoint formed by dividing both components of p by c.

const QPoint operator/ ( const QPoint & p, double c )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the QPoint formed by dividing both components of p by c.

Note that the result is truncated because points are held as integers.

QDataStream & operator<< ( QDataStream & s, const QPoint & p )

Writes point p to the stream s and returns a reference to the stream.

See also Format of the QDataStream operators.

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

Returns TRUE if p1 and p2 are equal; otherwise returns FALSE.

QDataStream & operator>> ( QDataStream & s, QPoint & p )

Reads a QPoint from the stream s into point p and returns a reference to the stream.

See also Format of the QDataStream operators.

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Qt version 3.0.4