QRegion is used with QPainter::setClipRegion() to limit the paint area to what needs to be painted. There is also a TQWidget::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). You can move a region using translate().
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You can test whether a region isNull(), isEmpty() or if it contains() a QPoint or QRect. The bounding rectangle is given by boundingRect().
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The function rects() gives a decomposition of the region into rectangles.
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Example of using complex regions:
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.nf
.br
void MyWidget::paintEvent( QPaintEvent * )
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{
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QPainter p; // our painter
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QRegion r1( QRect(100,100,200,80), // r1 = elliptic region
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QRegion::Ellipse );
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QRegion r2( QRect(100,120,90,30) ); // r2 = rectangular region
\fBWarning:\fR Due to window system limitations, the whole coordinate space for a region is limited to the points between -32767 and 32767 on Mac OS X and Windows 95/98/ME.
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See also QPainter::setClipRegion(), QPainter::setClipRect(), Graphics Classes, and Image Processing Classes.
.SS "Member Type Documentation"
.SH "QRegion::RegionType"
Specifies the shape of the region to be created.
.TP
\fCQRegion::Rectangle\fR - the region covers the entire rectangle.
.TP
\fCQRegion::Ellipse\fR - the region is an ellipse inside the rectangle.
.SH MEMBER FUNCTION DOCUMENTATION
.SH "QRegion::QRegion ()"
Constructs a null region.
.PP
See also isNull().
.SH "QRegion::QRegion ( int x, int y, int w, int h, RegionType t = Rectangle )"
Constructs a rectangular or elliptic region.
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If \fIt\fR is Rectangle, the region is the filled rectangle (\fIx\fR, \fIy\fR, \fIw\fR, \fIh\fR). If \fIt\fR is Ellipse, the region is the filled ellipse with center at (\fIx\fR + \fIw\fR / 2, \fIy\fR + \fIh\fR / 2) and size (\fIw\fR ,\fIh\fR ).
Constructs a polygon region from the point array \fIa\fR.
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If \fIwinding\fR is TRUE, the polygon region is filled using the winding algorithm, otherwise the default even-odd fill algorithm is used.
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This constructor may create complex regions that will slow down painting when used.
.SH "QRegion::QRegion ( const QRegion & r )"
Constructs a new region which is equal to region \fIr\fR.
.SH "QRegion::QRegion ( const QBitmap & bm )"
Constructs a region from the bitmap \fIbm\fR.
.PP
The resulting region consists of the pixels in bitmap \fIbm\fR that are \fCcolor1\fR, as if each pixel was a 1 by 1 rectangle.
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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().
.SH "QRegion::~QRegion ()"
Destroys the region.
.SH "QRect QRegion::boundingRect () const"
Returns the bounding rectangle of this region. An empty region gives a rectangle that is QRect::isNull().
.SH "bool QRegion::contains ( const QPoint & p ) const"
Returns TRUE if the region contains the point \fIp\fR; otherwise returns FALSE.
.SH "bool QRegion::contains ( const QRect & r ) const"
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
.PP
Returns TRUE if the region overlaps the rectangle \fIr\fR; otherwise returns FALSE.
.SH "QRegion QRegion::eor ( const QRegion & r ) const"
Returns a region which is the exclusive or (XOR) of this region and \fIr\fR.
.PP
<center>
.ce 1
.B "[Image Omitted]"
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</center>
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The figure shows the exclusive or of two elliptical regions.
.SH "HRGN QRegion::handle () const"
Returns the region's handle.
.SH "QRegion QRegion::intersect ( const QRegion & r ) const"
Returns a region which is the intersection of this region and \fIr\fR.
.PP
<center>
.ce 1
.B "[Image Omitted]"
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</center>
.PP
The figure shows the intersection of two elliptical regions.
.SH "bool QRegion::isEmpty () const"
Returns TRUE if the region is empty; otherwise returns FALSE. An empty region is a region that contains no points.
.PP
Example:
.PP
.nf
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QRegion r1( 10, 10, 20, 20 );
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QRegion r2( 40, 40, 20, 20 );
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QRegion r3;
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r1.isNull(); // FALSE
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r1.isEmpty(); // FALSE
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r3.isNull(); // TRUE
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r3.isEmpty(); // TRUE
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r3 = r1.intersect( r2 ); // r3 = intersection of r1 and r2
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r3.isNull(); // FALSE
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r3.isEmpty(); // TRUE
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r3 = r1.unite( r2 ); // r3 = union of r1 and r2
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r3.isNull(); // FALSE
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r3.isEmpty(); // FALSE
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.fi
.PP
See also isNull().
.SH "bool QRegion::isNull () const"
Returns TRUE if the region is a null region; otherwise returns FALSE.
.PP
A null region is a region that has not been initialized. A null region is always empty.
.PP
See also isEmpty().
.SH "bool QRegion::operator!= ( const QRegion & r ) const"
Returns TRUE if the region is different from \fIr\fR; otherwise returns FALSE.
Applies the intersect() function to this region and \fIr\fR. \fCr1&r2\fR is equivalent to \fCr1.intersect(r2)\fR
.PP
See also intersect().
.SH "QRegion & QRegion::operator&= ( const QRegion & r )"
Applies the intersect() function to this region and \fIr\fR and assigns the result to this region. \fCr1&=r2\fR is equivalent to \fCr1=r1.intersect(r2)\fR
Applies the subtract() function to this region and \fIr\fR. \fCr1-r2\fR is equivalent to \fCr1.subtract(r2)\fR
.PP
See also subtract().
.SH "QRegion & QRegion::operator-= ( const QRegion & r )"
Applies the subtract() function to this region and \fIr\fR and assigns the result to this region. \fCr1-=r2\fR is equivalent to \fCr1=r1.subtract(r2)\fR
.PP
See also subtract().
.SH "QRegion & QRegion::operator= ( const QRegion & r )"
Assigns \fIr\fR to this region and returns a reference to the region.
.SH "bool QRegion::operator== ( const QRegion & r ) const"
Returns TRUE if the region is equal to \fIr\fR; otherwise returns FALSE.
