| Home | All Classes | Main Classes | Annotated | Grouped Classes | Functions | |
The QCanvasPolygonalItem class provides a polygonal canvas item on a QCanvas. More...
#include <qcanvas.h>
Inherits QCanvasItem.
Inherited by QCanvasRectangle, QCanvasPolygon, QCanvasLine, and QCanvasEllipse.
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.
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.
Reimplemented from QCanvasItem.
Returns the QBrush used to fill the item, if filled.
See also setBrush().
Reimplemented from QCanvasItem.
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.
Returns TRUE if the polygonal item's area information has been invalidated; otherwise returns FALSE.
See also invalidate().
Returns the QPen used to draw the outline of the item, if any.
See also setPen().
See also QCanvasItem::rtti().
Reimplemented from QCanvasItem.
Reimplemented in QCanvasRectangle, QCanvasPolygon, QCanvasLine, and QCanvasEllipse.
See also setPen(), brush(), and drawShape().
Examples: canvas/canvas.cpp and chart/chartform_canvas.cpp.
See also setBrush(), pen(), and drawShape().
Examples: canvas/canvas.cpp and chart/chartform_canvas.cpp.
The default is to use the odd-even algorithm.
See also winding().
The default is to use the odd-even algorithm.
See also setWinding().
This file is part of the Qt toolkit. Copyright © 1995-2003 Trolltech. All Rights Reserved.
| Copyright © 2003 Trolltech | Trademarks | Qt version 3.1.2
|