Detailed 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.
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 Documentation
QCanvasPolygonalItem::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.
See also draw().
Reimplemented in QCanvasRectangle, QCanvasPolygon and QCanvasEllipse.
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: canvas/canvas.cpp and chart/chartform_canvas.cpp.
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: canvas/canvas.cpp and chart/chartform_canvas.cpp.
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().
This file is part of the Qt toolkit.
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