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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

(Note that these are not member 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 QPoint 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 to 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 and QRect.

Examples: forever/forever.cpp xform/xform.cpp drawlines/connect.cpp qmag/qmag.cpp


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.

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 since such distances apply to travelers who can only travel on a rectangular grid, like the streets of Manhattan.

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

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

Multiplies both x and y with c, and return 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*= ( int c )

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

Example:

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

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/= ( double c )

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

Example:

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

Note that the result is truncated.

QPoint & QPoint::operator/= ( int c )

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

Example:

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

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().

void QPoint::setY ( int y )

Sets the y coordinate of the point to y.

See also y() and setX().

int QPoint::x () const

Returns the x coordinate of the point.

See also setX() and y().

int QPoint::y () const

Returns the y coordinate of the point.

See also setY() and x().


Related Functions

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

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

Note that the result is truncated.

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

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

Note that the result is truncated.

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

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

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

Writes a QPoint to the stream and returns a reference to the stream.

See also Format of the QDataStream operators

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

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

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

Reads a QPoint from the stream and returns a reference to the stream.

See also Format of the QDataStream operators

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

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

Note that the result is truncated.

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

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

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

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

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

Returns TRUE if p1 and p2 are different, or FALSE if they are equal.

QPoint operator- (const QPoint & p)

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

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

Returns TRUE if p1 and p2 are equal, or FALSE if they are different.

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

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


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