QCanvasPolygonalItem(3qt)QCanvasPolygonalItem(3qt)NAME
QCanvasPolygonalItem - Polygonal canvas item on a QCanvas
SYNOPSIS
#include <qcanvas.h>
Inherits QCanvasItem.
Inherited by QCanvasRectangle, QCanvasPolygon, QCanvasLine, and
QCanvasEllipse.
Public Members
QCanvasPolygonalItem ( QCanvas * canvas )
virtual ~QCanvasPolygonalItem ()
virtual void setPen ( QPen p )
virtual void setBrush ( QBrush b )
QPen pen () const
QBrush brush () const
virtual QPointArray areaPoints () const = 0
virtual QPointArray areaPointsAdvanced () const
virtual QRect boundingRect () const
virtual int rtti () const
Protected Members
virtual void draw ( QPainter & p )
virtual void drawShape ( QPainter & p ) = 0
bool winding () const
void setWinding ( bool enable )
void invalidate ()
bool isValid () const
DESCRIPTION
The QCanvasPolygonalItem class provides a polygonal canvas item on a
QCanvas.
The mostly rectangular classes, such as QCanvasSprite and QCanvasText,
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. QCanvasPolygonalItem 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 QCanvasPolygonalItem's speed.
Note that all subclasses must call hide() in their destructor since
hide() needs to be able to access areaPoints().
Normally, QCanvasPolygonalItem 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 QCanvasItem::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, QCanvasPolygonalItem 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 QCanvasPolygonalItem
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
QCanvasItem::move() and QCanvasItem::moveBy(), or by setting
coordinates with QCanvasItem::setX(), QCanvasItem::setY() and
QCanvasItem::setZ().
See also Graphics Classes and Image Processing Classes.
MEMBER FUNCTION DOCUMENTATIONQCanvasPolygonalItem::QCanvasPolygonalItem ( QCanvas * canvas )
Constructs a QCanvasPolygonalItem on the canvas canvas.
QCanvasPolygonalItem::~QCanvasPolygonalItem () [virtual]
Note that all subclasses must call hide() in their destructor since
hide() needs to be able to access areaPoints().
QPointArray QCanvasPolygonalItem::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.
Reimplemented in QCanvasPolygon.
QPointArray QCanvasPolygonalItem::areaPointsAdvanced () const [virtual]
Returns the points the polygonal item will have after
QCanvasItem::advance(1) is called, i.e. what the points are when
advanced by the current xVelocity() and yVelocity().
QRect QCanvasPolygonalItem::boundingRect () const [virtual]
Returns the bounding rectangle of the polygonal item, based on
areaPoints().
Reimplemented from QCanvasItem.
QBrush QCanvasPolygonalItem::brush () const
Returns the QBrush used to fill the item, if filled.
See also setBrush().
void QCanvasPolygonalItem::draw ( QPainter & p ) [virtual protected]
Reimplemented from QCanvasItem, this draws the polygonal item by
setting the pen and brush for the item on the painter p and calling
drawShape().
Reimplemented from QCanvasItem.
void QCanvasPolygonalItem::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.
Warning: When you reimplement this function, make sure that you leave
the painter in the same state as you found it. For example, if you
start by calling QPainter::translate(50, 50), end your code by calling
QPainter::translate(-50, -50). Be also aware that the painter might
already have some transformations set (i.e., don't call
QPainter::resetXForm() when you're done).
See also draw().
Reimplemented in QCanvasRectangle, QCanvasPolygon, and QCanvasEllipse.
void QCanvasPolygonalItem::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 QCanvasPolygonalItem::isValid () const [protected]
Returns TRUE if the polygonal item's area information has not been
invalidated; otherwise returns FALSE.
See also invalidate().
QPen QCanvasPolygonalItem::pen () const
Returns the QPen used to draw the outline of the item, if any.
See also setPen().
int QCanvasPolygonalItem::rtti () const [virtual]
Returns 2 (QCanvasItem::Rtti_PolygonalItem).
See also QCanvasItem::rtti().
Reimplemented from QCanvasItem.
Reimplemented in QCanvasRectangle, QCanvasPolygon, QCanvasLine, and
QCanvasEllipse.
void QCanvasPolygonalItem::setBrush ( QBrush b ) [virtual]
Sets the QBrush used when drawing the polygonal item to the brush b.
See also setPen(), brush(), and drawShape().
Examples:
void QCanvasPolygonalItem::setPen ( QPen p ) [virtual]
Sets the QPen used when drawing the item to the pen p. Note that many
QCanvasPolygonalItems do not use the pen value.
See also setBrush(), pen(), and drawShape().
Examples:
void QCanvasPolygonalItem::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 QCanvasPolygonalItem::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().
SEE ALSO
http://doc.trolltech.com/qcanvaspolygonalitem.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
license file included in the distribution for a complete license
statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports help us to
help you. Thank you.
The definitive Qt documentation is provided in HTML format; it is
located at $QTDIR/doc/html and can be read using Qt Assistant or with a
web browser. This man page is provided as a convenience for those users
who prefer man pages, although this format is not officially supported
by Trolltech.
If you find errors in this manual page, please report them to qt-
bugs@trolltech.com. Please include the name of the manual page
(qcanvaspolygonalitem.3qt) and the Qt version (3.3.8).
Trolltech AS 2 February 2007 QCanvasPolygonalItem(3qt)