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The QRegion class specifies a clip region for a painter. More...
#include <qregion.h>
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.
See also QPainter::setClipRegion() and QPainter::setClipRect().
Rectangle - the region covers the entire rectangle
Ellipse - the region is an ellipse inside the rectangle
Constructs a null region.
See also isNull().
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().
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.
Constructs a new region which is equal to r.
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 ).
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Destructs the region.
Returns the bounding rectangle of this region. An empty region gives a rectangle that is QRect::isNull().
Returns TRUE if the region contains the point p, or FALSE if p is outside the region.
Returns TRUE if the region overlaps the rectangle r, or FALSE if r is completely outside the region.
Returns a region which is the exclusive or (XOR) of this region and r.
The figure shows the exclusive or of two elliptical regions.
Returns a region which is the intersection of this region and r.
The figure shows the intersection of two elliptical regions.
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().
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().
Returns TRUE if the region is different from r, or FALSE if the regions are equal.
r1&r2 is equivalent to r1.intersect(r2)
See also intersect().
r1&=r2 is equivalent to r1=r1.intersect(r2)
See also intersect().
r1+r2 is equivalent to r1.unite(r2)
See also unite() and operator|().
r1+=r2 is equivalent to r1=r1.unite(r2)
See also intersect().
r1-r2 is equivalent to r1.subtract(r2)
See also subtract().
r1-=r2 is equivalent to r1=r1.subtract(r2)
See also subtract().
Assigns r to this region and returns a reference to the region.
Returns TRUE if the region is equal to r, or FALSE if the regions are different.
r1^r2 is equivalent to r1.eor(r2)
See also eor().
r1^=r2 is equivalent to r1=r1.eor(r2)
See also eor().
r1|r2 is equivalent to r1.unite(r2)
See also unite() and operator+().
r1|=r2 is equivalent to r1=r1.unite(r2)
See also unite().
Returns an array of non-overlapping rectangles that make up the region.
The union of all the rectangles is equal to the original region.
Sets the region to be the given set of rectangles. The rectangles must be optimal Y-X sorted bands as follows:
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 ).
Translates (moves) the region dx along the X axis and dy along the Y axis.
Returns a region which is the union of this region and r.
The figure shows the union of two elliptical regions.
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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