Qt Toolkit - QRegion Class

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# QRegion Class Reference

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

`#include <qregion.h>`

List of all member functions.

## 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 Functions

(Note that these are not member functions.)

- QDataStream & operator>> (QDataStream & s, QRegion & r)
- QDataStream & operator<< (QDataStream & s, const QRegion & r)

## Detailed 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.

Some functions in QRegion are copyright (c) 1987 X Consortium. Please see src/3rdparty/kernel/qregion_qws.cpp for more information.

Some functions in QRegion for Qt/Embedded are copyright Digital Equipment Corporation:

Copyright 1987 by Digital Equipment Corporation, Maynard, Massachusetts.

All Rights Reserved

Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation, and that the name of Digital not be used in advertising or publicity pertaining to distribution of the software without specific, written prior permission.

DIGITAL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL DIGITAL BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

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.

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.

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.

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.

The figure shows the union of two elliptical regions.

## Related Functions

### 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

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