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 }

Public Functions

QRegion()
QRegion(int x, int y, int w, int h, RegionType t = Rectangle)
QRegion(const QRect &r, RegionType t = Rectangle)
QRegion(const QPolygon &a, Qt::FillRule fillRule = Qt::OddEvenFill)
QRegion(const QRegion &r)
QRegion(QRegion &&other)
QRegion(const QBitmap &bm)
QRect boundingRect() const
bool contains(const QPoint &p) const
bool contains(const QRect &r) const
QRegion intersected(const QRegion &r) const
QRegion intersected(const QRect &rect) const
bool intersects(const QRegion &region) const
bool intersects(const QRect &rect) const
bool isEmpty() const
bool isNull() const
int rectCount() const
QVector<QRect> rects() const
void setRects(const QRect *rects, int number)
QRegion subtracted(const QRegion &r) const
void swap(QRegion &other)
void translate(int dx, int dy)
void translate(const QPoint &point)
QRegion translated(int dx, int dy) const
QRegion translated(const QPoint &p) const
QRegion united(const QRegion &r) const
QRegion united(const QRect &rect) const
QRegion xored(const QRegion &r) const
operator QVariant() const
bool operator!=(const QRegion &other) const
QRegion operator&(const QRegion &r) const
QRegion operator&(const QRect &r) const
QRegion &operator&=(const QRegion &r)
QRegion &operator&=(const QRect &r)
QRegion operator+(const QRegion &r) const
QRegion operator+(const QRect &r) const
QRegion &operator+=(const QRegion &r)
QRegion &operator+=(const QRect &rect)
QRegion operator-(const QRegion &r) const
QRegion &operator-=(const QRegion &r)
QRegion &operator=(const QRegion &r)
QRegion &operator=(QRegion &&other)
bool operator==(const QRegion &r) const
QRegion operator^(const QRegion &r) const
QRegion &operator^=(const QRegion &r)
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

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() 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().

The function rects() 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, Windows CE 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.

Member Function Documentation

QRegion::QRegion()

Constructs an empty region.

See also isEmpty().

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

QRegion::QRegion(const QRect &r, RegionType t = Rectangle)

This is an overloaded function.

Create a region based on the rectange r with region type t.

If the rectangle is invalid a null region will be created.

See also QRegion::RegionType.

QRegion::QRegion(const QPolygon &a, Qt::FillRule fillRule = Qt::OddEvenFill)

Constructs a polygon region from the point array a with the fill rule specified by fillRule.

If fillRule is Qt::WindingFill, the polygon region is defined using the winding algorithm; if it is Qt::OddEvenFill, the odd-even fill algorithm is used.

Warning: This constructor can be used to create complex regions that will slow down painting when used.

QRegion::QRegion(const QRegion &r)

Constructs a new region which is equal to region r.

QRegion::QRegion(QRegion &&other)

Move-constructs a new region from region other. After the call, other is null.

This function was introduced in Qt 5.7.

See also isNull().

QRegion::QRegion(const QBitmap &bm)

Constructs a region from the bitmap bm.

The resulting region consists of the pixels in bitmap bm that are Qt::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().

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; otherwise returns false.

bool QRegion::contains(const QRect &r) const

This is an overloaded function.

Returns true if the region overlaps the rectangle r; otherwise returns false.

QRegion QRegion::intersected(const QRegion &r) const

Returns a region which is the intersection of this region and r.

Region Intersection

The figure shows the intersection of two elliptical regions.

This function was introduced in Qt 4.2.

See also subtracted(), united(), and xored().

QRegion QRegion::intersected(const QRect &rect) const

Returns a region which is the intersection of this region and the given rect.

This function was introduced in Qt 4.4.

See also subtracted(), united(), and xored().

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.

bool QRegion::intersects(const QRect &rect) const

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

This function was introduced in Qt 4.2.

bool QRegion::isEmpty() const

Returns true if the region is empty; otherwise returns false. An empty region is a region that contains no points.

Example:

QRegion r1(10, 10, 20, 20);
r1.isEmpty();               // false

QRegion r3;
r3.isEmpty();               // true

QRegion r2(40, 40, 20, 20);
r3 = r1.intersected(r2);    // r3: intersection of r1 and r2
r3.isEmpty();               // true

r3 = r1.united(r2);         // r3: union of r1 and r2
r3.isEmpty();               // false

bool QRegion::isNull() const

Returns true if the region is empty; otherwise returns false. An empty region is a region that contains no points. This function is the same as isEmpty

This function was introduced in Qt 5.0.

See also isEmpty().

int QRegion::rectCount() const

Returns the number of rectangles that will be returned in rects().

This function was introduced in Qt 4.6.

QVector<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.

See also setRects().

void QRegion::setRects(const QRect *rects, int number)

Sets the region using the array of rectangles specified by rects and number. The rectangles must be optimally Y-X sorted and follow these restrictions:

  • 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 in ascending order, with Y as the major sort key and X as the minor sort key.

See also rects().

QRegion QRegion::subtracted(const QRegion &r) const

Returns a region which is r subtracted from this region.

Region Subtraction

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

This function was introduced in Qt 4.2.

See also intersected(), united(), and xored().

void QRegion::swap(QRegion &other)

Swaps region other with this region. This operation is very fast and never fails.

This function was introduced in Qt 4.8.

void QRegion::translate(int dx, int dy)

Translates (moves) the region dx along the X axis and dy along the Y axis.

void QRegion::translate(const QPoint &point)

This is an overloaded function.

Translates the region point.x() along the x axis and point.y() along the y axis, relative to the current position. Positive values move the region to the right and down.

Translates to the given point.

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().

QRegion QRegion::translated(const QPoint &p) const

This is an overloaded function.

Returns a copy of the regtion that is translated p.x() along the x axis and p.y() along the y axis, relative to the current position. Positive values move the rectangle to the right and down.

This function was introduced in Qt 4.1.

See also translate().

QRegion QRegion::united(const QRegion &r) const

Returns a region which is the union of this region and r.

Region Union

The figure shows the union of two elliptical regions.

This function was introduced in Qt 4.2.

See also intersected(), subtracted(), and xored().

QRegion QRegion::united(const QRect &rect) const

Returns a region which is the union of this region and the given rect.

This function was introduced in Qt 4.4.

See also intersected(), subtracted(), and xored().

QRegion QRegion::xored(const QRegion &r) const

Returns a region which is the exclusive or (XOR) of this region and r.

Region XORed

The figure shows the exclusive or of two elliptical regions.

This function was introduced in Qt 4.2.

See also intersected(), united(), and subtracted().

QRegion::operator QVariant() const

Returns the region as a QVariant

bool QRegion::operator!=(const QRegion &other) const

Returns true if this region is different from the other region; otherwise returns false.

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().

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

This is an overloaded function.

This function was introduced in Qt 4.4.

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

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

See also intersected().

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

This is an overloaded function.

This function was introduced in Qt 4.4.

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 QRect &r) const

This is an overloaded function.

This function was introduced in Qt 4.4.

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 intersected().

QRegion &QRegion::operator+=(const QRect &rect)

Returns a region that is the union of this region with the specified rect.

See also united().

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().

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

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

See also subtracted().

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

Assigns r to this region and returns a reference to the region.

QRegion &QRegion::operator=(QRegion &&other)

Move-assigns other to this QRegion instance.

This function was introduced in Qt 5.2.

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

Returns true if the region is equal to r; otherwise returns false.

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().

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 &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 &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.

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