# 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 |

## 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 ®ion) 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.

`[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.

## 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.

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

## 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.