TQCanvasPolygonalItem Class

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# TQCanvasPolygonalItem Class Reference
[canvas module]

The TQCanvasPolygonalItem class provides a polygonal canvas item on a TQCanvas. More...

`#include <ntqcanvas.h>`

Inherits TQCanvasItem.

Inherited by TQCanvasRectangle, TQCanvasPolygon, TQCanvasLine, and TQCanvasEllipse.

List of all member functions.

## Public Members

- TQCanvasPolygonalItem ( TQCanvas * canvas )
- virtual ~TQCanvasPolygonalItem ()
- virtual void setPen ( TQPen p )
- virtual void setBrush ( TQBrush b )
- TQPen pen () const
- TQBrush brush () const
- virtual TQPointArray areaPoints () const = 0
- virtual TQPointArray areaPointsAdvanced () const
- virtual TQRect boundingRect () const
- virtual int rtti () const

## Protected Members

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

## Detailed Description

The TQCanvasPolygonalItem class provides a polygonal canvas item on a TQCanvas.

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 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 TQCanvasPolygonalItem's speed.

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

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 will 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 TQPen and TQBrush constructors). You can change this with setPen() and setBrush(), but note that some TQCanvasPolygonalItem 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 TQCanvasItem::move() and TQCanvasItem::moveBy(), or by setting coordinates with TQCanvasItem::setX(), TQCanvasItem::setY() and TQCanvasItem::setZ().

See also Graphics Classes and Image Processing Classes.

## Member Function Documentation

### TQCanvasPolygonalItem::TQCanvasPolygonalItem ( TQCanvas * canvas )

Constructs a TQCanvasPolygonalItem on the canvas canvas.

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

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

### TQPointArray TQCanvasPolygonalItem::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 TQCanvasPolygon.

### TQPointArray TQCanvasPolygonalItem::areaPointsAdvanced () const`[virtual]`

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

### TQRect TQCanvasPolygonalItem::boundingRect () const`[virtual]`

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

Reimplemented from TQCanvasItem.

### TQBrush TQCanvasPolygonalItem::brush () const

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

See also setBrush().

### void TQCanvasPolygonalItem::draw ( TQPainter & p )`[virtual protected]`

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

Reimplemented from TQCanvasItem.

### void TQCanvasPolygonalItem::drawShape ( TQPainter & 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 TQPainter::translate(50, 50), end your code by calling TQPainter::translate(-50, -50). Be also aware that the painter might already have some transformations set (i.e., don't call TQPainter::resetXForm() when you're done).

See also draw().

Reimplemented in TQCanvasRectangle, TQCanvasPolygon, and TQCanvasEllipse.

### void TQCanvasPolygonalItem::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 TQCanvasPolygonalItem::isValid () const`[protected]`

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

See also invalidate().

### TQPen TQCanvasPolygonalItem::pen () const

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

See also setPen().

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

Returns 2 (TQCanvasItem::Rtti_PolygonalItem).

See also TQCanvasItem::rtti().

Reimplemented from TQCanvasItem.

Reimplemented in TQCanvasRectangle, TQCanvasPolygon, TQCanvasLine, and TQCanvasEllipse.

### void TQCanvasPolygonalItem::setBrush ( TQBrush b )`[virtual]`

Sets the TQBrush 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 TQCanvasPolygonalItem::setPen ( TQPen p )`[virtual]`

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

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

Examples: canvas/canvas.cpp and chart/chartform_canvas.cpp.

### void TQCanvasPolygonalItem::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 TQCanvasPolygonalItem::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().

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