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# Q3CanvasPolygonalItem Class Reference
[Qt3Support module]

The Q3CanvasPolygonalItem class provides a polygonal canvas item on a Q3Canvas. More...

    #include <Q3CanvasPolygonalItem>

This class is part of the Qt 3 support library. It is provided to keep old source code working. We strongly advise against using it in new code. See Porting to Qt 4 for more information.

Note to Qt Desktop Light Edition users: This class is only available in the Qt Desktop Edition.

Inherits Q3CanvasItem.

Inherited by Q3CanvasEllipse, Q3CanvasLine, Q3CanvasPolygon, and Q3CanvasRectangle.

- List of all members, including inherited members

### Public Functions

- Q3CanvasPolygonalItem ( Q3Canvas * canvas )
- virtual ~Q3CanvasPolygonalItem ()
- virtual Q3PointArray areaPoints () const = 0
- virtual Q3PointArray areaPointsAdvanced () const
- virtual QRect boundingRect () const
- QBrush brush () const
- QPen pen () const
- virtual int rtti () const
- virtual void setBrush ( QBrush b )
- virtual void setPen ( QPen p )

- 34 public functions inherited from Q3CanvasItem

### Protected Functions

- virtual void draw ( QPainter & p )
- virtual void drawShape ( QPainter & p ) = 0
- void invalidate ()
- bool isValid () const
- void setWinding ( bool enable )
- bool winding () const

- 1 protected function inherited from Q3CanvasItem

## Detailed Description

The Q3CanvasPolygonalItem class provides a polygonal canvas item on a Q3Canvas.

The mostly rectangular classes, such as Q3CanvasSprite and Q3CanvasText, use the object's bounding rectangle for movement, repainting and collision calculations. For most other items, the bounding rectangle can be far too large -- a diagonal line being the worst case, and there are many other cases which are also bad. Q3CanvasPolygonalItem provides polygon-based bounding rectangle handling, etc., which is much faster for non-rectangular items.

Derived classes should try to define as small an area as possible to maximize efficiency, but the polygon must definitely be contained completely within the polygonal area. Calculating the exact requirements is usually difficult, but if you allow a small overestimate it can be easy and quick, while still getting almost all of Q3CanvasPolygonalItem's speed.

Note that all subclasses must call hide() in their destructor since hide() needs to be able to access areaPoints().

Normally, Q3CanvasPolygonalItem uses the odd-even algorithm for determining whether an object intersects this object. You can change this to the winding algorithm using setWinding().

The bounding rectangle is available using boundingRect(). The points bounding the polygonal item are retrieved with areaPoints(). Use areaPointsAdvanced() to retrieve the bounding points the polygonal item will have after Q3CanvasItem::advance(1) has been called.

If the shape of the polygonal item is about to change while the item is visible, call invalidate() before updating with a different result from areaPoints().

By default, Q3CanvasPolygonalItem objects have a black pen and no brush (the default QPen and QBrush constructors). You can change this with setPen() and setBrush(), but note that some Q3CanvasPolygonalItem subclasses only use the brush, ignoring the pen setting.

The polygonal item can be drawn on a painter with draw(). Subclasses must reimplement drawShape() to draw themselves.

Like any other canvas item polygonal items can be moved with Q3CanvasItem::move() and Q3CanvasItem::moveBy(), or by setting coordinates with Q3CanvasItem::setX(), Q3CanvasItem::setY() and Q3CanvasItem::setZ().

See also QtCanvas.

## Member Function Documentation

### Q3CanvasPolygonalItem::Q3CanvasPolygonalItem ( Q3Canvas * canvas )

Constructs a Q3CanvasPolygonalItem on the canvas canvas.

### Q3CanvasPolygonalItem::~Q3CanvasPolygonalItem () `[virtual]`

Note that all subclasses must call hide() in their destructor since hide() needs to be able to access areaPoints().

### Q3PointArray Q3CanvasPolygonalItem::areaPoints () const `[pure virtual]`

This function must be reimplemented by subclasses. It must return the points bounding (i.e. outside and not touching) the shape or drawing errors will occur.

### Q3PointArray Q3CanvasPolygonalItem::areaPointsAdvanced () const `[virtual]`

Returns the points the polygonal item will have after Q3CanvasItem::advance(1) is called, i.e. what the points are when advanced by the current xVelocity() and yVelocity().

### QRect Q3CanvasPolygonalItem::boundingRect () const `[virtual]`

Returns the bounding rectangle of the polygonal item, based on areaPoints().

Reimplemented from Q3CanvasItem.

### QBrush Q3CanvasPolygonalItem::brush () const

Returns the QBrush used to fill the item, if filled.

See also setBrush().

### void Q3CanvasPolygonalItem::draw ( QPainter & p ) `[virtual protected]`

Reimplemented from Q3CanvasItem, this draws the polygonal item by setting the pen and brush for the item on the painter p and calling drawShape().

Reimplemented from Q3CanvasItem.

### void Q3CanvasPolygonalItem::drawShape ( QPainter & p ) `[pure virtual protected]`

Subclasses must reimplement this function to draw their shape. The pen and brush of p are already set to pen() and brush() prior to calling this function.

See also draw().

### void Q3CanvasPolygonalItem::invalidate () `[protected]`

Invalidates all information about the area covered by the canvas item. The item will be updated automatically on the next call that changes the item's status, for example, move() or update(). Call this function if you are going to change the shape of the item (as returned by areaPoints()) while the item is visible.

### bool Q3CanvasPolygonalItem::isValid () const `[protected]`

Returns true if the polygonal item's area information has not been invalidated; otherwise returns false.

See also invalidate().

### QPen Q3CanvasPolygonalItem::pen () const

Returns the QPen used to draw the outline of the item, if any.

See also setPen().

### int Q3CanvasPolygonalItem::rtti () const `[virtual]`

Returns 2 (Q3CanvasItem::Rtti_PolygonalItem).

Reimplemented from Q3CanvasItem.

See also Q3CanvasItem::rtti().

### void Q3CanvasPolygonalItem::setBrush ( QBrush b ) `[virtual]`

Sets the QBrush used when drawing the polygonal item to the brush b.

See also setPen(), brush(), and drawShape().

### void Q3CanvasPolygonalItem::setPen ( QPen p ) `[virtual]`

Sets the QPen used when drawing the item to the pen p. Note that many Q3CanvasPolygonalItems do not use the pen value.

See also setBrush(), pen(), and drawShape().

### void Q3CanvasPolygonalItem::setWinding ( bool enable ) `[protected]`

If enable is true, the polygonal item will use the winding algorithm to determine the "inside" of the polygon; otherwise the odd-even algorithm will be used.

The default is to use the odd-even algorithm.

See also winding().

### bool Q3CanvasPolygonalItem::winding () const `[protected]`

Returns true if the polygonal item uses the winding algorithm to determine the "inside" of the polygon. Returns false if it uses the odd-even algorithm.

The default is to use the odd-even algorithm.

See also setWinding().