QRegion Class

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(), QPainterPath

Specifies the shape of the region to be created.

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.

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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.

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Constructs an empty region.

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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).

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.

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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.

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().

Constructs a new region which is equal to region r.

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

This function was introduced in Qt 5.7.

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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.

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

Same as begin().

This function was introduced in Qt 5.8.

Same as end().

This function was introduced in Qt 5.8.

Returns true if the region contains the point p; otherwise returns false.

This is an overloaded function.

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

Same as rbegin().

This function was introduced in Qt 5.8.

Same as rend().

This function was introduced in Qt 5.8.

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.

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Returns a QRegion that is equivalent to the given hrgn.

This function was introduced in Qt 6.0.

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

The figure shows the intersection of two elliptical regions.

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

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

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

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

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.

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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.

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

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.

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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.

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).

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

Returns a HRGN that is equivalent to the given region.

This function was introduced in Qt 6.0.

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

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.

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.

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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.

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

The figure shows the union of two elliptical regions.

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

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

The figure shows the exclusive or of two elliptical regions.

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Returns the region as a QVariant

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

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

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This is an overloaded function.

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).

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This is an overloaded function.

Applies the united() function to this region and r. r1+r2 is equivalent to r1.united(r2).

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This is an overloaded function.

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).

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

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

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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).

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

Move-assigns other to this QRegion instance.

This function was introduced in Qt 5.2.

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

Applies the xored() function to this region and r. r1^r2 is equivalent to r1.xored(r2).

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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).

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Applies the united() function to this region and r. r1|r2 is equivalent to r1.united(r2).

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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).

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Writes the region r to the stream s and returns a reference to the stream.

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

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