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# QPolygon Class Reference
[QtGui module]

The QPolygon class provides a vector of points using integer precision. More...

     #include <QPolygon>

Inherits QVector<QPoint>.

Inherited by Q3PointArray.

Note: All the functions in this class are reentrant.

- List of all members, including inherited members

### Public Functions

- QPolygon ()
- QPolygon ( int size )
- QPolygon ( const QPolygon & polygon )
- QPolygon ( const QVector<QPoint> & points )
- QPolygon ( const QRect & rectangle, bool closed = false )
- ~QPolygon ()
- QRect boundingRect () const
- bool containsPoint ( const QPoint & point, Qt::FillRule fillRule ) const
- QPolygon intersected ( const QPolygon & r ) const
- void point ( int index, int * x, int * y ) const
- QPoint point ( int index ) const
- void putPoints ( int index, int nPoints, int firstx, int firsty, ... )
- void putPoints ( int index, int nPoints, const QPolygon & fromPolygon, int fromIndex = 0 )
- void setPoint ( int index, int x, int y )
- void setPoint ( int index, const QPoint & point )
- void setPoints ( int nPoints, const int * points )
- void setPoints ( int nPoints, int firstx, int firsty, ... )
- QPolygon subtracted ( const QPolygon & r ) const
- void translate ( int dx, int dy )
- void translate ( const QPoint & offset )
- QPolygon united ( const QPolygon & r ) const
- operator QVariant () const

- 64 public functions inherited from QVector

### Related Non-Members

- QDataStream & operator<< ( QDataStream & stream, const QPolygon & polygon )
- QDataStream & operator>> ( QDataStream & stream, QPolygon & polygon )

### Additional Inherited Members

- 2 static public members inherited from QVector

## Detailed Description

The QPolygon class provides a vector of points using integer precision.

A QPolygon object is a QVector<QPoint>. The easiest way to add points to a QPolygon is to use QVector's streaming operator, as illustrated below:

             QPolygon polygon;
             polygon << QPoint(10, 20) << QPoint(20, 30);

In addition to the functions provided by QVector, QPolygon provides some point-specific functions.

Each point in a polygon can be retrieved by passing its index to the point() function. To populate the polygon, QPolygon provides the setPoint() function to set the point at a given index, the setPoints() function to set all the points in the polygon (resizing it to the given number of points), and the putPoints() function which copies a number of given points into the polygon from a specified index (resizing the polygon if necessary).

QPolygon provides the boundingRect() and translate() functions for geometry functions. Use the QMatrix::map() function for more general transformations of QPolygons.

The QPolygon class is implicitly shared.

See also QVector, QPolygonF, and QLine.

## Member Function Documentation

### QPolygon::QPolygon ()

Constructs a polygon with no points.

See also QVector::isEmpty().

### QPolygon::QPolygon ( int size )

Constructs a polygon of the given size. Creates an empty polygon if size == 0.

See also QVector::isEmpty().

### QPolygon::QPolygon ( const QPolygon & polygon )

Constructs a copy of the given polygon.

See also setPoints().

### QPolygon::QPolygon ( const QVector<QPoint> & points )

Constructs a polygon containing the specified points.

See also setPoints().

### QPolygon::QPolygon ( const QRect & rectangle, bool closed = false )

Constructs a polygon from the given rectangle. If closed is false, the polygon just contains the four points of the rectangle ordered clockwise, otherwise the polygon's fifth point is set to rectangle.topLeft().

Note that the bottom-right corner of the rectangle is located at (rectangle.x() + rectangle.width(), rectangle.y() + rectangle.height()).

See also setPoints().

### QPolygon::~QPolygon ()

Destroys the polygon.

### QRect QPolygon::boundingRect () const

Returns the bounding rectangle of the polygon, or QRect(0, 0, 0, 0) if the polygon is empty.

See also QVector::isEmpty().

### bool QPolygon::containsPoint ( const QPoint & point, Qt::FillRule fillRule ) const

Returns true if the given point is inside the polygon according to the specified fillRule; otherwise returns false.

This function was introduced in Qt 4.3.

### QPolygon QPolygon::intersected ( const QPolygon & r ) const

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

Set operations on polygons will treat the polygons as areas. Non-closed polygons will be treated as implicitly closed.

This function was introduced in Qt 4.3.

### void QPolygon::point ( int index, int * x, int * y ) const

Extracts the coordinates of the point at the given index to *x and *y (if they are valid pointers).

See also setPoint().

### QPoint QPolygon::point ( int index ) const

This is an overloaded function.

Returns the point at the given index.

### void QPolygon::putPoints ( int index, int nPoints, int firstx, int firsty, ... )

Copies nPoints points from the variable argument list into this polygon from the given index.

The points are given as a sequence of integers, starting with firstx then firsty, and so on. The polygon is resized if `index+nPoints` exceeds its current size.

The example code creates a polygon with three points (4,5), (6,7) and (8,9), by expanding the polygon from 1 to 3 points:

             QPolygon polygon(1);
             polygon[0] = QPoint(4, 5);
             polygon.putPoints(1, 2, 6,7, 8,9);

The following code has the same result, but here the putPoints() function overwrites rather than extends:

             QPolygon polygon(3);
             polygon.putPoints(0, 3, 4,5, 0,0, 8,9);
             polygon.putPoints(1, 1, 6,7);

See also setPoints().

### void QPolygon::putPoints ( int index, int nPoints, const QPolygon & fromPolygon, int fromIndex = 0 )

This is an overloaded function.

Copies nPoints points from the given fromIndex ( 0 by default) in fromPolygon into this polygon, starting at the specified index. For example:

             QPolygon polygon1;
             polygon1.putPoints(0, 3, 1,2, 0,0, 5,6);
             // polygon1 is now the three-point polygon(1,2, 0,0, 5,6);

             QPolygon polygon2;
             polygon2.putPoints(0, 3, 4,4, 5,5, 6,6);
             // polygon2 is now (4,4, 5,5, 6,6);

             polygon1.putPoints(2, 3, polygon2);
             // polygon1 is now the five-point polygon(1,2, 0,0, 4,4, 5,5, 6,6);

### void QPolygon::setPoint ( int index, int x, int y )

Sets the point at the given index to the point specified by (x, y).

See also point(), putPoints(), and setPoints().

### void QPolygon::setPoint ( int index, const QPoint & point )

This is an overloaded function.

Sets the point at the given index to the given point.

### void QPolygon::setPoints ( int nPoints, const int * points )

Resizes the polygon to nPoints and populates it with the given points.

The example code creates a polygon with two points (10, 20) and (30, 40):

             static const int points[] = { 10, 20, 30, 40 };
             QPolygon polygon;
             polygon.setPoints(2, points);

See also setPoint() and putPoints().

### void QPolygon::setPoints ( int nPoints, int firstx, int firsty, ... )

This is an overloaded function.

Resizes the polygon to nPoints and populates it with the points specified by the variable argument list. The points are given as a sequence of integers, starting with firstx then firsty, and so on.

The example code creates a polygon with two points (10, 20) and (30, 40):

             QPolygon polygon;
             polygon.setPoints(2, 10, 20, 30, 40);

### QPolygon QPolygon::subtracted ( const QPolygon & r ) const

Returns a polygon which is r subtracted from this polygon.

Set operations on polygons will treat the polygons as areas. Non-closed polygons will be treated as implicitly closed.

This function was introduced in Qt 4.3.

### void QPolygon::translate ( int dx, int dy )

Translates all points in the polygon by (dx, dy).

### void QPolygon::translate ( const QPoint & offset )

This is an overloaded function.

Translates all points in the polygon by the given offset.

### QPolygon QPolygon::united ( const QPolygon & r ) const

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

Set operations on polygons, will treat the polygons as areas, and implicitly close the polygon.

This function was introduced in Qt 4.3.

See also intersected() and subtracted().

### QPolygon::operator QVariant () const

Returns the polygon as a QVariant

## Related Non-Members

### QDataStream & operator<< ( QDataStream & stream, const QPolygon & polygon )

Writes the given polygon to the given stream, and returns a reference to the stream.

This function was introduced in Qt 4.4.

See also Format of the QDataStream Operators.

### QDataStream & operator>> ( QDataStream & stream, QPolygon & polygon )

Reads a polygon from the given stream into the given polygon, and returns a reference to the stream.

This function was introduced in Qt 4.4.

See also Format of the QDataStream Operators.