Re: NSLayoutManager and best override point for temporary attributes
Re: NSLayoutManager and best override point for temporary attributes
- Subject: Re: NSLayoutManager and best override point for temporary attributes
- From: Martin Wierschin <email@hidden>
- Date: Wed, 30 Sep 2009 18:50:30 -0700
Hi Keith,
I have certain custom text attributes that are used in my
NSTextStorage to which I would like to add temporary attributes via
the NSLayoutManager.
What version of OSX are you testing under? Under Leopard there's a bug
in -[NSLayoutManager
temporaryAttribute:atCharacterIndex:longestEffectiveRange:inRange:]
that calculates effective ranges that are too short. For specific test
cases this caused big inefficiencies in the text system. I believe
this bug is fixed in Snow Leopard.
more recently I have taken to overriding NSLayoutManager's -
temporaryAttributesAtCharacterIndex:effectiveRange:
If this is too slow, then I'd look to using some kind of cache for
your calculations. But really, NSLayoutManager's temporary attributes
are already a cache; one likely to be specifically designed for high
performance index/run access. I think your original idea of setting
temporary attributes whenever text changes would be the most efficient.
Perhaps you're recalculating too much, too often? I don't know the
access patterns for temporary attributes, but I would guess they are
only queried when associated text is displayed on screen. If that's
the case, you could fix them up lazily, eg: whenever text changes just
note down that the attributes are dirty in that range. Your temporary
attribute methods in your NSLayoutManager subclass can then ensure
that temporary attributes are not dirty before they are returned.
If none of that is efficient enough, you could rig up a NSTextStorage
subclass that has two sets of attributes: one set for private use and
another derived set which only the layout system sees.
Hopefully some of that helps,
~Martin
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