The mostly rectangular classes, such as TQCanvasSprite and TQCanvasText, 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. TQCanvasPolygonalItem 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 \fIdefinitely\fR 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 TQCanvasPolygonalItem's speed.
Normally, TQCanvasPolygonalItem 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 \fIwill\fR have after TQCanvasItem::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, TQCanvasPolygonalItem 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 TQCanvasPolygonalItem subclasses only use the brush, ignoring the pen setting.
Like any other canvas item polygonal items can be moved with TQCanvasItem::move() and TQCanvasItem::moveBy(), or by setting coordinates with TQCanvasItem::setX(), TQCanvasItem::setY() and TQCanvasItem::setZ().
This function must be reimplemented by subclasses. It \fImust\fR return the points bounding (i.e. outside and not touching) the shape or drawing errors will occur.
Returns the points the polygonal item \fIwill\fR have after TQCanvasItem::advance(1) is called, i.e. what the points are when advanced by the current xVelocity() and yVelocity().
.SH "void TQCanvasPolygonalItem::draw ( QPainter & p )\fC [virtual protected]\fR"
Reimplemented from TQCanvasItem, this draws the polygonal item by setting the pen and brush for the item on the painter \fIp\fR and calling drawShape().
Subclasses must reimplement this function to draw their shape. The pen and brush of \fIp\fR are already set to pen() and brush() prior to calling this function.
.PP
\fBWarning:\fR 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).
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.
If \fIenable\fR 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.
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.
