[Qt-interest] QGraphicsOpacityEffect performance worse than QGraphicsItem::setOpacity()

[Josiah Bryan]

Josiah Bryan wrote:
> This is such a disappointment that I'm looking at ripping the code for 
> the drop shadow out of the library and just using it straight in my own 
> app and do my own caching if the library can't provide acceptable 
> performance.

Well, I'm over my disappointment and I've moved on, now that I've got 
the desired effects without having to use the library itself. I've 
copied the static blurred() implementation from qpixmapfilters.cpp into 
my own code base (ImageFilters.cpp in r193 at 
http://code.google.com/p/dviz/source/detail?r=193), and after reading 
the dropshadow algorithm in the same file, implemented it in my text 
rendering item. For the implementation, see line 307 in TextBoxContent.cpp:

http://code.google.com/p/dviz/source/browse/trunk/src/items/TextBoxContent.cpp?spec=svn193&r=193#307

In addition to integrating the blur code directly, I'm using very 
aggressive app-wide pixmap caching using QPixmapCache. All graphics 
items in my app use underlying QObject-based models (AbstractVisualItem) 
that fire signals when an attribute is changed and keep an internal 
quint32 revision counter. I only dirty the rendered shadow cache when 
the revision counter on the underlying model changes. So I could create 
and destroy a "visual delegate" for the model item multiple times 
without having to re-render the cached pixmap. Anyway, as I said, very 
aggressive caching. May not be appros for others, but works for my app.

Hope that helps any who may follow in similar frustrations.

Cheers!
-josiah

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Josiah Bryan
Productive Concepts, Inc.
jbryan at pciint.com
(765) 964-6009, ext. 224