Qt 4.3: QRegion Class Reference

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# QRegion Class Reference
[QtGui module]

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

     #include <QRegion>

- List of all members, including inherited members
- Obsolete members
- Qt 3 support members

### Public Types

- enum RegionType { Rectangle, Ellipse }

### Public Functions

- QRegion ()
- QRegion ( int x, int y, int w, int h, RegionType t = Rectangle )
- QRegion ( const QPolygon & a, Qt::FillRule fillRule = Qt::OddEvenFill )
- QRegion ( const QRegion & r )
- QRegion ( const QBitmap & bm )
- QRegion ( const QRect & r, RegionType t = Rectangle )
- ~QRegion ()
- QRect boundingRect () const
- bool contains ( const QPoint & p ) const
- bool contains ( const QRect & r ) const
- Handle handle () const
- QRegion intersected ( const QRegion & r ) const
- bool intersects ( const QRegion & region ) const
- bool intersects ( const QRect & rect ) const
- bool isEmpty () const
- QVector<QRect> rects () const
- void setRects ( const QRect * rects, int number )
- QRegion subtracted ( const QRegion & r ) const
- 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 xored ( const QRegion & r ) const
- operator QVariant () const
- bool operator!= ( const QRegion & other ) 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 )
- const QRegion operator- ( const QRegion & r ) const
- QRegion & operator-= ( const QRegion & r )
- QRegion & operator= ( const QRegion & r )
- bool 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 )

### Related Non-Members

- 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 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 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
     }

QRegion is an implicitly shared class.

Warning: Due to window system limitations, the whole coordinate space for a region is limited to the points between -32767 and 32767 on Windows 95/98/ME. You can circumvent this limitation by using a QPainterPath.

### Additional License Information

For Qt/X11 and Qtopia Core, parts of this class rely on code obtained under the following license:

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.

Constant | Value | Description
--- | --- | ---
`QRegion::Rectangle` | `0` | the region covers the entire rectangle.
`QRegion::Ellipse` | `1` | the 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 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 ( 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().

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

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 ()

Destroys 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; otherwise returns false.

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

This is an overloaded member function, provided for convenience.

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

### Handle QRegion::handle () const

Returns a platform-specific region handle. The `Handle` type is `HRGN` on Windows, `Region` on X11, and `RgnHandle` on Mac OS X. On Qtopia Core it is `void *`.

Warning: This function is not portable.

### QRegion QRegion::intersected ( 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.

This function was introduced in Qt 4.2.

### 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

This is an overloaded member function, provided for convenience.

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.isNull();                // false
     r1.isEmpty();               // false

     QRegion r2(40, 40, 20, 20);
     QRegion r3;
     r3.isNull();                // true
     r3.isEmpty();               // true

     r3 = r1.intersected(r2);    // r3: intersection of r1 and r2
     r3.isNull();                // false
     r3.isEmpty();               // true

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

### 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.

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::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 member function, provided for convenience.

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 member function, provided for convenience.

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.

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::xored ( 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.

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.

### 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().

### 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().

### 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 intersected().

### 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().

### 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.

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

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

### 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 & operator<< ( QDataStream & s, const QRegion & r )

This is an overloaded member function, provided for convenience.

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 )

This is an overloaded member function, provided for convenience.

Reads a region from the stream s into r and returns a reference to the stream.

See also Format of the QDataStream operators.