QRegion Class

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

Header:	#include <QRegion>
CMake:	find_package(Qt6 COMPONENTS Gui REQUIRED) target_link_libraries(mytarget PRIVATE Qt6::Gui)
qmake:	QT += gui

• List of all members, including inherited members

Public Types

enum	RegionType { Rectangle, Ellipse }
	const_iterator
	const_reverse_iterator

Public Functions

	QRegion(const QBitmap &bm)
	QRegion(QRegion &&other)
	QRegion(const QRegion &r)
	QRegion(const QPolygon &a, Qt::FillRule fillRule = Qt::OddEvenFill)
	QRegion(const QRect &r, QRegion::RegionType t = Rectangle)
	QRegion(int x, int y, int w, int h, QRegion::RegionType t = Rectangle)
	QRegion()
QRegion &	operator=(QRegion &&other)
QRegion &	operator=(const QRegion &r)
QRegion::const_iterator	begin() const
QRect	boundingRect() const
QRegion::const_iterator	cbegin() const
QRegion::const_iterator	cend() const
bool	contains(const QPoint &p) const
bool	contains(const QRect &r) const
QRegion::const_reverse_iterator	crbegin() const
QRegion::const_reverse_iterator	crend() const
QRegion::const_iterator	end() 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
QRegion::const_reverse_iterator	rbegin() const
int	rectCount() const
QRegion::const_reverse_iterator	rend() const
void	setRects(const QRect *rects, int number)
QRegion	subtracted(const QRegion &r) const
void	swap(QRegion &other)
HRGN	toHRGN() 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	united(const QRect &rect) const
QRegion	xored(const QRegion &r) const
QVariant	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)
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)

Static Public Members

QRegion

fromHRGN(HRGN hrgn)

Related Non-Members

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
}

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.

[since 5.8] 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().

[since 5.8] 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(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().

[since 5.7] 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 QRegion &r)

Constructs a new region which is equal to region r.

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.

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

This is an overloaded function.

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

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

See also QRegion::RegionType.

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).

QRegion::QRegion()

Constructs an empty region.

See also isEmpty().

[since 5.2] QRegion &QRegion::operator=(QRegion &&other)

Move-assigns other to this QRegion instance.

This function was introduced in Qt 5.2.

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

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

[since 5.8] QRegion::const_iterator QRegion::begin() const

Returns a const_iterator pointing to the beginning of the range of non-overlapping rectangles that make up the region.

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

This function was introduced in Qt 5.8.

See also rbegin(), cbegin(), and end().

QRect QRegion::boundingRect() const

Returns the bounding rectangle of this region. An empty region gives a rectangle that is QRect::isNull().

[since 5.8] QRegion::const_iterator QRegion::cbegin() const

Same as begin().

This function was introduced in Qt 5.8.

[since 5.8] QRegion::const_iterator QRegion::cend() const

Same as end().

This function was introduced in Qt 5.8.

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.

[since 5.8] QRegion::const_reverse_iterator QRegion::crbegin() const

Same as rbegin().

This function was introduced in Qt 5.8.

[since 5.8] QRegion::const_reverse_iterator QRegion::crend() const

Same as rend().

This function was introduced in Qt 5.8.

[since 5.8] QRegion::const_iterator QRegion::end() const

Returns a const_iterator pointing to one past the end of non-overlapping rectangles that make up the region.

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

This function was introduced in Qt 5.8.

See also rend(), cend(), and begin().

[static, since 6.0] QRegion QRegion::fromHRGN(HRGN hrgn)

Returns a QRegion that is equivalent to the given hrgn.

This function was introduced in Qt 6.0.

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.

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.

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

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

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

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

Returns true if this region intersects with rect, 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.

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

[since 5.0] 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().

[since 5.8] QRegion::const_reverse_iterator QRegion::rbegin() const

Returns a const_reverse_iterator pointing to the beginning of the range of non-overlapping rectangles that make up the region.

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

This function was introduced in Qt 5.8.

See also begin(), crbegin(), and rend().

int QRegion::rectCount() const

Returns the number of rectangles that this region is composed of. Same as end() - begin().

[since 5.8] QRegion::const_reverse_iterator QRegion::rend() const

Returns a const_reverse_iterator pointing to one past the end of the range of non-overlapping rectangles that make up the region.

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

This function was introduced in Qt 5.8.

See also end(), crend(), and rbegin().

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.

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).

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.

[since 6.0] HRGN QRegion::toHRGN() const

Returns a HRGN that is equivalent to the given region.

This function was introduced in Qt 6.0.

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.

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.

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.

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.

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.

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

QVariant 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.

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.

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.

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().

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().