QRegion Class Reference
The QRegion class specifies a clip region for a painter.
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#include <qregion.h>
List of all member functions.
Public Members
Related Functions
(Note that these are not member functions.)
- QDataStream & operator>> (QDataStream & s, QRegion & r)
- QDataStream & operator<< (QDataStream & s, const 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() 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 unite(), intersect(), subtract() or eor() (exclusive or). Use
translate() to move a region.
You can test if a region isNull(), isEmpty() or if it contains()
a QPoint or QRect. The bounding rectangle is given by boundingRect().
The function rects() gives a decomposition of the region into rectangles.
Example of using complex regions:
void MyWidget::paintEvent( QPaintEvent * )
{
QPainter p; // our painter
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.intersect( r2 ); // r3 = intersection
p.begin( this ); // start painting widget
p.setClipRegion( r3 ); // set clip region
... // paint clipped graphics
p.end(); // painting done
}
QRegion is an implicitely shared class.
Due to window system limitations, the width and height of a region
is limited to 65535 on Unix/X11.
Some functions in QRegion are copyright (c) 1987 X Consortium.
Please see src/3rdparty/kernel/qregion_qws.cpp for more information.
Some functions in QRegion for Qt/Embedded are copyright Digital
Equipment Corporation:
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() and QPainter::setClipRect().
Member Type Documentation
Determines the shape of the region to be created.
Rectangle - the region covers the entire rectangle
Ellipse - the region is an ellipse inside the rectangle
Member Function Documentation
QRegion::QRegion ()
Constructs a null region.
See also isNull().
QRegion::QRegion ( const QBitmap & bm )
Constructs a region from the bitmap bm.
The resulting region consists of the pixels in bm that are 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 QPointArray & a, bool winding=FALSE )
Constructs a polygon region from the point array a.
If winding is TRUE, the polygon
region is filled using the winding algorithm, otherwise the default
even-odd fill algorithm is used.
This constructor may create complex regions that will slow
down painting when used.
QRegion::QRegion ( const QRegion & r )
Constructs a new region which is equal to r.
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 ellipse with center at (x + w / 2, y + h / 2) and
size (w ,h ).
QRegion::~QRegion ()
Destructs 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, or FALSE if p is
outside the region.
bool QRegion::contains ( const QRect & r ) const
Returns TRUE if the region overlaps the rectangle r, or FALSE if r is
completely outside the region.
QRegion QRegion::eor ( 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.
QRegion QRegion::intersect ( 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.
bool QRegion::isEmpty () const
Returns TRUE if the region is empty, or FALSE if it is non-empty.
An empty region is a region that contains no points.
Example:
QRegion r1( 10, 10, 20, 20 );
QRegion r2( 40, 40, 20, 20 );
QRegion r3;
r1.isNull(); // FALSE
r1.isEmpty(); // FALSE
r3.isNull(); // TRUE
r3.isEmpty(); // TRUE
r3 = r1.intersect( r2 ); // r3 = intersection of r1 and r2
r3.isNull(); // FALSE
r3.isEmpty(); // TRUE
r3 = r1.unite( r2 ); // r3 = union of r1 and r2
r3.isNull(); // FALSE
r3.isEmpty(); // FALSE
See also isNull().
bool QRegion::isNull () const
Returns TRUE if the region is a null region, otherwise FALSE.
A null region is a region that has not been initialized. A
null region is always empty.
See also isEmpty().
bool QRegion::operator!= ( const QRegion & r ) const
Returns TRUE if the region is different from r, or FALSE if the regions
are equal.
QRegion QRegion::operator& ( const QRegion & r ) const
r1&r2 is equivalent to r1.intersect(r2)
See also intersect().
QRegion& QRegion::operator&= ( const QRegion & r )
r1&=r2 is equivalent to r1=r1.intersect(r2)
See also intersect().
QRegion QRegion::operator+ ( const QRegion & r ) const
r1+r2 is equivalent to r1.unite(r2)
See also unite() and operator|().
QRegion& QRegion::operator+= ( const QRegion & r )
r1+=r2 is equivalent to r1=r1.unite(r2)
See also intersect().
QRegion QRegion::operator- ( const QRegion & r ) const
r1-r2 is equivalent to r1.subtract(r2)
See also subtract().
QRegion& QRegion::operator-= ( const QRegion & r )
r1-=r2 is equivalent to r1=r1.subtract(r2)
See also subtract().
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, or FALSE if the regions are
different.
QRegion QRegion::operator^ ( const QRegion & r ) const
r1^r2 is equivalent to r1.eor(r2)
See also eor().
QRegion& QRegion::operator^= ( const QRegion & r )
r1^=r2 is equivalent to r1=r1.eor(r2)
See also eor().
QRegion QRegion::operator| ( const QRegion & r ) const
r1|r2 is equivalent to r1.unite(r2)
See also unite() and operator+().
QRegion& QRegion::operator|= ( const QRegion & r )
r1|=r2 is equivalent to r1=r1.unite(r2)
See also unite().
QArray<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.
void QRegion::setRects ( const QRect * rects, int num )
Sets the region to be the given set of rectangles. The rectangles
must be optimal Y-X sorted bands as follows:
- 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 ascendingly by Y as the major sort key
and X as the minor sort key.
QRegion QRegion::subtract ( 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 ).
void QRegion::translate ( int dx, int dy )
Translates (moves) the region dx along the X axis and dy along the Y axis.
QRegion QRegion::unite ( 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.
Related Functions
Reads a region from the stream s into r and returns a
reference to the stream.
See also Format of the QDataStream operators
Writes the region r to the stream s and returns a reference to
the stream.
See also Format of the QDataStream operators
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