QRegion(3qt)

NAME
QRegion - Clip region for a painter

#include <qregion.h>

  Public Members
enum RegionType { Rectangle, Ellipse }
QRegion ()
QRegion ( int x, int y, int w, int h, RegionType = Rectangle )
QRegion ( const QRect &, RegionType = Rectangle )
QRegion ( const QPointArray &, bool winding=FALSE )
QRegion ( const QRegion & )
QRegion ( const QBitmap & )
~QRegion ()
QRegion& operator= ( const QRegion & )
bool isNull () const
bool isEmpty () const
bool contains ( const QPoint & p ) const
bool contains ( const QRect & r ) const
void translate ( int dx, int dy )
QRegion unite ( const QRegion & ) const
QRegion intersect ( const QRegion & ) const
QRegion subtract ( const QRegion & ) const
QRegion eor ( const QRegion & ) const
QRect boundingRect () const
QArray<QRect> rects () const
void setRects ( const QRect *, int )
QRegion operator| ( const QRegion & ) const
QRegion operator+ ( const QRegion & ) const
QRegion operator& ( const QRegion & ) const
QRegion operator- ( const QRegion & ) const
QRegion operator^ ( const QRegion & ) const
QRegion& operator|= ( const QRegion & )
QRegion& operator+= ( const QRegion & )
QRegion& operator&= ( const QRegion & )
QRegion& operator-= ( const QRegion & )
QRegion& operator^= ( const QRegion & )
bool operator== ( const QRegion & ) const
bool operator!= ( const QRegion & r ) const

RELATED FUNCTION DOCUMENTATION
(Note that these are not member functions.)
QDataStream & operator>> (QDataStream & s, QRegion & r)
QDataStream & operator<< (QDataStream & s, const QRegion & r)

DESCRIPTION
The QRegion class specifies a clip region for a painter.

QRegion is used with QPainter::setClipRegion() to limit the paint area to what needs to be painted. There is also a QWidget::repaint() that takes a QRegion parameter. QRegion is the best tool for reducing flicker.

A region can be created from a rectangle, an ellipse, a polygon or a bitmap. Complex regions may be created by combining simple regions, using unite(), intersect(), subtract() or eor() (exclusive or). Use translate() to move a region.

You can test if a region isNull(), isEmpty() or if it contains() a QPoint or QRect. The bounding rectangle is given by boundingRect().

The function rects() gives a decomposition of the region into rectangles.

Example of using complex regions:

    void MyWidget::paintEvent( QPaintEvent * )
    {
        QPainter p;                             // our painter
        QRegion r1( QRect(100,100,200,80),      // r1 = elliptic region
                    QRegion::Ellipse );
        QRegion r2( QRect(100,120,90,30) );     // r2 = rectangular region
        QRegion r3 = r1.intersect( r2 );        // r3 = intersection
        p.begin( this );                        // start painting widget
        p.setClipRegion( r3 );                  // set clip region
        ...                                     // paint clipped graphics
        p.end();                                // painting done
    }

QRegion is an implicitely shared class.

Due to window system limitations, the width and height of a region is limited to 65535 on Unix/X11.

See also QPainter::setClipRegion() and QPainter::setClipRect().

  Member Type Documentation

QRegion::RegionType
Determines the shape of the region to be created.

Rectangle - the region covers the entire rectangle

Ellipse - the region is an ellipse inside the rectangle

MEMBER FUNCTION DOCUMENTATION

QRegion::QRegion ()
Constructs a null region.

See also isNull().

QRegion::QRegion ( const QBitmap & bm )
Constructs a region from the bitmap bm.

The resulting region consists of the pixels in bm that are color1, as if each pixel was a 1 by 1 rectangle.

This constructor may create complex regions that will slow down painting when used. Note that drawing masked pixmaps can be done much faster using QPixmap::setMask().

QRegion::QRegion ( const QPointArray & a, bool winding=FALSE )
Constructs a polygon region from the point array a.

If winding is TRUE, the polygon region is filled using the winding algorithm, otherwise the default even-odd fill algorithm is used.

This constructor may create complex regions that will slow down painting when used.

QRegion::QRegion ( const QRegion & r )
Constructs a new region which is equal to r.

QRegion::QRegion ( int x, int y, int w, int h, RegionType t = Rectangle )
Constructs a rectangular or elliptic region.

If t is Rectangle, the region is the filled rectangle (x, y, w, h). If t is Ellipse, the region is the filled ellipse ellipse with center at (x + w / 2, y + h / 2) and size (w ,h ).

QRegion::~QRegion ()
Destructs the region.

QRect QRegion::boundingRect () const
Returns the bounding rectangle of this region. An empty region gives a rectangle that is QRect::isNull().

bool QRegion::contains ( const QPoint & p ) const
Returns TRUE if the region contains the point p, or FALSE if p is outside the region.

bool QRegion::contains ( const QRect & r ) const
Returns TRUE if the region overlaps the rectangle r, or FALSE if r is completely outside the region.

QRegion QRegion::eor ( const QRegion & r ) const
Returns a region which is the exclusive or (XOR) of this region and r.

[Image Omitted]

The figure shows the exclusive or of two elliptical regions.

QRegion QRegion::intersect ( const QRegion & r ) const
Returns a region which is the intersection of this region and r.

[Image Omitted]

The figure shows the intersection of two elliptical regions.

bool QRegion::isEmpty () const
Returns TRUE if the region is empty, or FALSE if it is non-empty. An empty region is a region that contains no points.

Example:

    QRegion r1( 10, 10, 20, 20 );
    QRegion r2( 40, 40, 20, 20 );
    QRegion r3;
    r1.isNull();                // FALSE
    r1.isEmpty();               // FALSE
    r3.isNull();                // TRUE
    r3.isEmpty();               // TRUE
    r3 = r1.intersect( r2 );    // r3 = intersection of r1 and r2
    r3.isNull();                // FALSE
    r3.isEmpty();               // TRUE
    r3 = r1.unite( r2 );        // r3 = union of r1 and r2
    r3.isNull();                // FALSE
    r3.isEmpty();               // FALSE

See also isNull().

bool QRegion::isNull () const
Returns TRUE if the region is a null region, otherwise FALSE.

A null region is a region that has not been initialized. A null region is always empty.

See also isEmpty().

bool QRegion::operator!= ( const QRegion & r ) const
Returns TRUE if the region is different from r, or FALSE if the regions are equal.

QRegion QRegion::operator& ( const QRegion & r ) const
r1&r2 is equivalent to r1.intersect(r2)

See also intersect().

QRegion& QRegion::operator&= ( const QRegion & r )
r1&=r2 is equivalent to r1=r1.intersect(r2)

See also intersect().

QRegion QRegion::operator+ ( const QRegion & r ) const
r1+r2 is equivalent to r1.unite(r2)

See also unite() and operator|().

QRegion& QRegion::operator+= ( const QRegion & r )
r1+=r2 is equivalent to r1=r1.unite(r2)

See also intersect().

QRegion QRegion::operator- ( const QRegion & r ) const
r1-r2 is equivalent to r1.subtract(r2)

See also subtract().

QRegion& QRegion::operator-= ( const QRegion & r )
r1-=r2 is equivalent to r1=r1.subtract(r2)

See also subtract().

QRegion & QRegion::operator= ( const QRegion & r )
Assigns r to this region and returns a reference to the region.

bool QRegion::operator== ( const QRegion & r ) const
Returns TRUE if the region is equal to r, or FALSE if the regions are different.

QRegion QRegion::operator^ ( const QRegion & r ) const
r1^r2 is equivalent to r1.eor(r2)

See also eor().

QRegion& QRegion::operator^= ( const QRegion & r )
r1^=r2 is equivalent to r1=r1.eor(r2)

See also eor().

QRegion QRegion::operator| ( const QRegion & r ) const
r1|r2 is equivalent to r1.unite(r2)

See also unite() and operator+().

QRegion& QRegion::operator|= ( const QRegion & r )
r1|=r2 is equivalent to r1=r1.unite(r2)

See also unite().

QArray<QRect> QRegion::rects () const
Returns an array of non-overlapping rectangles that make up the region.

The union of all the rectangles is equal to the original region.

void QRegion::setRects ( const QRect * rects, int num )
Sets the region to be the given set of rectangles. The rectangles must be optimal Y-X sorted bands as follows:

The rectangles must not intersect

All rectangles with a given top coordinate must have the same height.

No two rectangles may abut horizontally (they should be combined into a single wider rectangle in that case).

The rectangles must be sorted ascendingly by Y as the major sort key and X as the minor sort key.

QRegion QRegion::subtract ( const QRegion & r ) const
Returns a region which is r subtracted from this region.

[Image Omitted]

The figure shows the result when the ellipse on the right is subtracted from the ellipse on the left. (left-right ).

void QRegion::translate ( int dx, int dy )
Translates (moves) the region dx along the X axis and dy along the Y axis.

QRegion QRegion::unite ( const QRegion & r ) const
Returns a region which is the union of this region and r.

[Image Omitted]

The figure shows the union of two elliptical regions.

RELATED FUNCTION DOCUMENTATION

QDataStream & operator>> (QDataStream & s, QRegion & r)
Reads a region from the stream s into r and returns a reference to the stream.

See also Format of the QDataStream operators

QDataStream & operator<< (QDataStream & s, const QRegion & r)
Writes the region r to the stream s and returns a reference to the stream.

See also Format of the QDataStream operators

SEE ALSO
http://doc.trolltech.com/qregion.html http://www.trolltech.com/faq/tech.html

COPYRIGHT
Copyright 1992-2001 Trolltech AS, http://www.trolltech.com. See the license file included in the distribution for a complete license statement.

AUTHOR
Generated automatically from the source code.

BUGS
If you find a bug in Qt, please report it as described in http://doc.trolltech.com/bughowto.html. Good bug reports make our job much simpler. Thank you.

In case of content or formattting problems with this manual page, please report them to qt-bugs@trolltech.com. Please include the name of the manual page (qregion.3qt) and the Qt version (2.3.5).