[Qt-interest] QGraphicsEffect drawing

[Anton Chernov]

class Q_GUI_EXPORT QGraphicsEffect : public QObject
{
    Q_OBJECT
    Q_FLAGS(ChangeFlags)
    Q_PROPERTY(bool enabled READ isEnabled WRITE setEnabled NOTIFY
enabledChanged)
public:
[...]
friend class QGraphicsItem;
friend class QGraphicsItemPrivate;
friend class QGraphicsScenePrivate;
friend class QWidget;
friend class QWidgetPrivate;
[...]
}

it seems that only QGraphicsScenePrivate has access to protected
effect members... if i reimplement ::render i still would need to
render the effects...

something is missing...

how does the actual source pixmap come to an effect? It seems that it
looks in the cache for a pixmap, but who and where renders this pixmap
to the cache?

2011/7/16 Malyushytsky, Alex <alex at wai.com>:
> How many subclasses of QGraphicsScene you have?
> Create a single subclass MyCraphicsScene which would implement flag and always derive from it instead of QGraphicsScene.
>
> Alex
>
> -----Original Message-----
> From: Anton Chernov [mailto:mechernov at gmail.com]
> Sent: Friday, July 15, 2011 1:26 PM
> To: Malyushytsky, Alex
> Cc: qt-interest at trolltech.com
> Subject: Re: [Qt-interest] QGraphicsEffect drawing
>
> I want avoid this because i every class i would have to have such a
> flag - that's miserable :) Bad c++ is miserable too, but takes less
> place in code :)
>
> 2011/7/15 Malyushytsky, Alex <alex at wai.com>:
>> QGraphicsEffect is base class for the for graphics effects.
>>
>> This probably means that when you set effect you do not create instance of QGraphicsEffect, but
>> QGraphicsBlurEffect, QGraphicsColorizeEffect, QGraphicsDropShadowEffect, or QGraphicsOpacityEffect.
>>
>> So what you are trying to do below is illegal, cause none of the above classes are derived from
>> BadEffectAccessor.
>>
>> I can't give you direct answer on your question, but I don't think you need id.
>>
>> void QGraphicsScene::render calls
>>   virtual void drawItems(...) to draw items.
>>
>> All you need to make standard render work the way you want is override so it skips items you don't want to draw ( set flag before calling it for example ).
>>
>>
>> Regards,
>>  Alex
>>
>>
>> -----Original Message-----
>> From: qt-interest-bounces+alex=wai.com at qt.nokia.com [mailto:qt-interest-bounces+alex=wai.com at qt.nokia.com] On Behalf Of Anton Chernov
>> Sent: Friday, July 15, 2011 12:47 AM
>> To: qt-interest at trolltech.com
>> Subject: [Qt-interest] QGraphicsEffect drawing
>>
>> Hi,
>>
>> I have a problem drawing QGraphicsEffects - a have a scene with lots
>> of items, but when rendering for print only particular items should be
>> drawn.
>> If i would call
>>
>> QGraphicsScene::render( ... )
>>
>> all will be drawn, so I use a custom renderer. Everything draws good
>> except the graphics effects - their
>>
>> draw( QPainter* painter )
>>
>> is protected.
>>
>> class BadEffectAccessor : public QGraphicsEffect
>> {
>>   public:
>>      void publicDraw( QPainter* painter ) { draw( painter ); }
>> };
>>
>> [...]
>> if( text->graphicsEffect() ) {
>>   BadEffectAccessor* accessor = static_cast< BadEffectAccessor* >(
>> text->graphicsEffect() );
>>   accessor->publicDraw( painter );
>> }
>> [...]
>>
>> Does not help, nothing is drawn! How do I draw the effects?
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