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

Public Types
enum	RegionType

Public Methods
	QRegion ()

	QRegion (const QBitmap &bitmap)

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

	QRegion (const QRect &rect, RegionType t=Rectangle)

	QRegion (const QRegion &other)

	QRegion (int x, int y, int w, int h, RegionType t=Rectangle)

QRect	boundingRect () const

bool	contains (const QPoint &point) const

bool	contains (const QRect &rect) const

QRegion	intersected (const QRect &rect) const

QRegion	intersected (const QRegion &region) const

bool	intersects (const QRect &rect) const

bool	intersects (const QRegion &region) const

bool	isEmpty () const

bool	isNull () const

	operator QVariant () const

bool	operator!= (const QRegion &other) const

QRegion	operator& (const QRect &rect) const

QRegion	operator& (const QRegion &other) const

QRegion &	operator&= (const QRect &rect)

QRegion &	operator&= (const QRegion &other)

QRegion	operator+ (const QRect &rect) const

QRegion	operator+ (const QRegion &other) const

QRegion &	operator+= (const QRect &rect)

QRegion &	operator+= (const QRegion &other)

QRegion	operator- (const QRegion &other) const

QRegion &	operator-= (const QRegion &other)

QRegion &	operator= (const QRegion &other)

QRegion &	operator= (QRegion &&other)

bool	operator== (const QRegion &other) const

QRegion	operator^ (const QRegion &other) const

QRegion &	operator^= (const QRegion &other)

QRegion	operator\| (const QRegion &other) const

QRegion &	operator\|= (const QRegion &other)

int	rectCount () const

QVector< QRect >	rects () const

void	setRects (const QRect *rects, int rectCount)

QRegion	subtracted (const QRegion &region) const

void	swap (QRegion &other)

void	translate (const QPoint &point)

void	translate (int dx, int dy)

QRegion	translated (const QPoint &point) const

QRegion	translated (int dx, int dy) const

QRegion	united (const QRect &rect) const

QRegion	united (const QRegion &region) const

QRegion	xored (const QRegion &region) const

Friends
QDataStream &	operator<< (QDataStream &stream, const QRegion &region)

QDataStream &	operator>> (QDataStream &stream, QRegion &region)

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), QRegion::Ellipse);  // r1: elliptic region
 
    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 X11 platforms parts of this class rely on code obtained under the following licenses:

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.

See also: QPainter::setClipRegion(), QPainter::setClipRect(), QPainterPath

Member Enumeration 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.

Constructor & Destructor 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 &	rect,
		RegionType	t = `Rectangle`
	)

Create a region based on the rectangle rect with region type t. If the rectangle is invalid a null region will be created.

See also: QRegion::RegionType

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

Constructs a polygon region from the point array polygon 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 & other )

Copy constructs a new QRegion from other.

QRegion::QRegion ( const QBitmap & bitmap )

Constructs a region from the bitmap.

The resulting region consists of the pixels in bitmap 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. Drawing masked pixmaps can be done much faster using QPixmap::setMask().

Method Documentation

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 & point ) const

Returns true if the region contains the given point, otherwise returns false.

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

Returns true if the region overlaps the rectangle rect, otherwise returns false.

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

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

See also: subtracted(), united(), xored()

QRegion QRegion::intersected ( const QRegion & region ) const

Returns a region which is the intersection of this QRegion and region. The following figure shows the intersection of two elliptical regions.

See also: subtracted(), united(), xored()

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

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

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

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

bool QRegion::isEmpty ( ) const

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

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. Equivalent to calling isEmpty().

QRegion::operator QVariant ( ) const

Returns the region as a QVariant.

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

inline

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

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

This is an overloaded function.

QRegion QRegion::operator& ( const QRegion & other ) const

Applies the intersected() method to the current QRegion and other. The calculation r1 & r2 is equivalent to r1.intersected(r2).

See also: intersected()

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

This is an overloaded function.

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

Applies the intersected() method to this QRegion and other and assigns the result to this region. The calculation r1 &= r2 is equivalent to r1 = r1.intersected(r2).

See also: intersected()

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

This is an overloaded function.

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

Applies the united() method to this QRegion and other. The calculation r1 + r2 is equivalent to r1.united(r2).

See also: united(), operator|()

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

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

See also: united()

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

Applies the united() method to this QRegion and other and assigns the result to this region. The calculation r1 += r2 is equivalent to r1 = r1.united(r2).

See also: intersected()

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

Applies the subtracted() method to this QRegion and other . The calculation r1 - r2 is equivalent to r1.subtracted(r2).

See also: subtracted()

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

Applies the subtracted() method to this QRegion and other and assigns the result to this region. The calculation r1 -= r2 is equivalent to r1 = r1.subtracted(r2).

See also: subtracted()

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

Copy assigns from other and returns a reference to this object.

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

inline

Move assigns from other and returns a reference to this object.

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

Returns true if this QRegion is equal to other, otherwise returns false.

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

Applies the xored() method to this region and other. The calculation r1 ^ r2 is equivalent to r1.xored(r2).

See also: xored()

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

Applies the xored() method to this QRegion and other and assigns the result to this region. The calculation r1 ^= r2 is equivalent to r1 = r1.xored(r2).

See also: xored()

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

Applies the united() method to this QRegion and other. The calculation r1 | r2 is equivalent to r1.united(r2).

See also: united(), operator+()

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

Applies the united() method to this QRegion and other and assigns the result to this region. The calculation r1 |= r2 is equivalent to r1 = r1.united(r2).

See also: united()

int QRegion::rectCount ( ) const

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

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	rectCount
	)

Sets the region using the array of rectangles specified by rects and rectCount. 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 & region ) const

Returns a region which is the passed region subtracted from the current QRegion. The following figure shows the result when the ellipse on the right is subtracted from the ellipse on the left (left - right).

See also: intersected(), united(), xored()

void QRegion::swap ( QRegion & other )

inline

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

void QRegion::translate ( const QPoint & point )

inline

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.

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

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

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

inline

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

See also: translate()

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

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