QRegion Class

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

Header: #include <QRegion>
qmake: QT += gui

Public Types

enum RegionType { Rectangle, Ellipse }
typedef const_iterator
typedef const_reverse_iterator

Public Functions

QRegion(int x, int y, int w, int h, QRegion::RegionType t = Rectangle)
bool intersects(const QRegion &region) const
QRegion translated(int dx, int dy) const
QVariant operator QVariant() const
const QRegion operator&(const QRegion &r) const
const QRegion operator&(const QRect &r) const
QRegion &operator&=(const QRect &r)
const QRegion operator+(const QRegion &r) const
const QRegion operator+(const QRect &r) const
const QRegion operator-(const QRegion &r) const
const QRegion operator^(const QRegion &r) const
QRegion &operator^=(const QRegion &r)
const QRegion operator|(const QRegion &r) const
QRegion &operator|=(const QRegion &r)
QDataStream &operator<<(QDataStream &s, const QRegion &r)
QDataStream &operator>>(QDataStream &s, QRegion &r)

Detailed Description

QRegion is used with QPainter::setClipRegion() to limit the paint area to what needs to be painted. There is also a QWidget::repaint() function that takes a QRegion parameter. QRegion is the best tool for minimizing the amount of screen area to be updated by a repaint.

This class is not suitable for constructing shapes for rendering, especially as outlines. Use QPainterPath to create paths and shapes for use with QPainter.

QRegion is an implicitly shared class.

Creating and Using Regions

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 united(), intersected(), subtracted(), or xored() (exclusive or). You can move a region using translate().

You can test whether a region isEmpty() or if it contains() a QPoint or QRect. The bounding rectangle can be found with boundingRect().

Iteration over the region (with begin(), end(), or C++11 ranged-for loops) gives a decomposition of the region into rectangles.

Example of using complex regions:


  void MyWidget::paintEvent(QPaintEvent *)
  {
      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.intersected(r2);        // r3: intersection

      QPainter painter(this);
      painter.setClipRegion(r3);
      ...                                     // paint clipped graphics
  }

Additional License Information

On Embedded Linux and X11 platforms, parts of this class rely on code obtained under the following licenses:

Copyright (c) 1987 X Consortium

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Except as contained in this notice, the name of the X Consortium shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization from the X Consortium.


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(), QPainter::setClipRect(), and QPainterPath.

Member Type Documentation

enum QRegion::RegionType

Specifies the shape of the region to be created.

ConstantValueDescription
QRegion::Rectangle0the region covers the entire rectangle.
QRegion::Ellipse1the region is an ellipse inside the rectangle.

typedef QRegion::const_iterator

An iterator over the non-overlapping rectangles that make up the region.

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

QRegion does not offer mutable iterators.

This typedef was introduced in Qt 5.8.

See also begin() and end().

typedef QRegion::const_reverse_iterator

A reverse iterator over the non-overlapping rectangles that make up the region.

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

QRegion does not offer mutable iterators.

This typedef was introduced in Qt 5.8.

See also rbegin() and rend().

Member Function Documentation

QRegion::QRegion(int x, int y, int w, int h, QRegion::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 with center at (x + w / 2, y + h / 2) and size (w ,h).

bool QRegion::intersects(const QRegion &region) const

Returns true if this region intersects with region, otherwise returns false.

This function was introduced in Qt 4.2.

QRegion QRegion::translated(int dx, int dy) const

Returns a copy of the region that is translated dx along the x axis and dy along the y axis, relative to the current position. Positive values move the region to the right and down.

This function was introduced in Qt 4.1.

See also translate().

QVariant QRegion::operator QVariant() const

Returns the region as a QVariant

const QRegion QRegion::operator&(const QRegion &r) const

Applies the intersected() function to this region and r. r1&r2 is equivalent to r1.intersected(r2).

See also intersected().

const QRegion QRegion::operator&(const QRect &r) const

This is an overloaded function.

This function was introduced in Qt 4.4.

QRegion &QRegion::operator&=(const QRect &r)

This is an overloaded function.

This function was introduced in Qt 4.4.

const QRegion QRegion::operator+(const QRegion &r) const

Applies the united() function to this region and r. r1+r2 is equivalent to r1.united(r2).

See also united() and operator|().

const QRegion QRegion::operator+(const QRect &r) const

This is an overloaded function.

This function was introduced in Qt 4.4.

const QRegion QRegion::operator-(const QRegion &r) const

Applies the subtracted() function to this region and r. r1-r2 is equivalent to r1.subtracted(r2).

See also subtracted().

const QRegion QRegion::operator^(const QRegion &r) const

Applies the xored() function to this region and r. r1^r2 is equivalent to r1.xored(r2).

See also xored().

QRegion &QRegion::operator^=(const QRegion &r)

Applies the xored() function to this region and r and assigns the result to this region. r1^=r2 is equivalent to r1 = r1.xored(r2).

See also xored().

const QRegion QRegion::operator|(const QRegion &r) const

Applies the united() function to this region and r. r1|r2 is equivalent to r1.united(r2).

See also united() and operator+().

QRegion &QRegion::operator|=(const QRegion &r)

Applies the united() function to this region and r and assigns the result to this region. r1|=r2 is equivalent to r1 = r1.united(r2).

See also united().

Related Non-Members

QDataStream &QRegion::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.

QDataStream &QRegion::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.