# QPolygon Class

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

Header: | #include <QPolygon> |

qmake: | QT += gui |

Inherits: | QVector |

**Note:** All functions in this class are reentrant.

## Public Functions

QPolygon(const QPolygon &polygon) | |

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

QPolygon(const QVector<QPoint> &points) | |

QPolygon(int size) | |

QPolygon() | |

~QPolygon() | |

QRect | boundingRect() const |

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

QPolygon | intersected(const QPolygon &r) const |

bool | intersects(const QPolygon &p) const |

void | point(int index, int *x, int *y) const |

QPoint | point(int index) const |

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

void | putPoints(int index, int nPoints, int firstx, int firsty, ...) |

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 | swap(QPolygon &other) |

void | translate(int dx, int dy) |

void | translate(const QPoint &offset) |

QPolygon | translated(int dx, int dy) const |

QPolygon | translated(const QPoint &offset) const |

QPolygon | united(const QPolygon &r) const |

QVariant | operator QVariant() const |

## Related Non-Members

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

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

## Detailed Description

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:

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 QTransform::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(const QPolygon &*polygon*)

Constructs a copy of the given *polygon*.

**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(const QVector<QPoint> &*points*)

Constructs a polygon containing the specified *points*.

**See also **setPoints().

### QPolygon::QPolygon(int *size*)

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

**See also **QVector::isEmpty().

### QPolygon::QPolygon()

Constructs a polygon with no points.

**See also **QVector::isEmpty().

### 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.

**See also **intersects().

### bool QPolygon::intersects(const QPolygon &*p*) const

Returns `true`

if the current polygon intersects at any point the given polygon *p*. Also returns `true`

if the current polygon contains or is contained by any part of *p*.

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 5.10.

**See also **intersected().

### 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*, 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::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:

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::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::swap(QPolygon &*other*)

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

This function was introduced in Qt 4.8.

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

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

**See also **translated().

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

This is an overloaded function.

Translates all points in the polygon by the given *offset*.

**See also **translated().

### QPolygon QPolygon::translated(int *dx*, int *dy*) const

Returns a copy of the polygon that is translated by (*dx*, *dy*).

This function was introduced in Qt 4.6.

**See also **translate().

### QPolygon QPolygon::translated(const QPoint &*offset*) const

This is an overloaded function.

Returns a copy of the polygon that is translated by the given *offset*.

This function was introduced in Qt 4.6.

**See also **translate().

### 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().

### QVariant 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 **Serializing Qt Data Types.

### 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 **Serializing Qt Data Types.

© 2023 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.