Re: C-n is very slow in Font-Lock mode

[David Kastrup <dak@gnu.org>]

"Eli Zaretskii" <eliz@gnu.org> writes:

>> From: Richard Stallman <rms@gnu.org>
>> CC: emacs-devel@gnu.org
>> Date: Tue, 26 Apr 2005 06:05:41 -0400
>> 
>>     > It turns out that vertical-motion was fontifying all the text that
>>     > it moved over.  That seems to be easy to fix.
>> 
>>     Did you try my suggestion of customizing jit-lock-defer-time?
>> 
>> No, because I want to fix this, not work around it.  vertical-motion
>> is a cursor motion function.  It should not fontify anything.
>
> As David pointed out, vertical-motion does that for a good reason:
> fontification can well change the pixel size of the glyphs that Emacs
> needs to display.
>
> I think jit-lock-defer-time _is_ the way to avoid the slowness if
> you are willing to see the text unfontified for a fraction of a
> second.

I think that a separate value of 0 where is one not willing to see
text unfontified, but willing to have motion calculated with a still
unfontified text, would make perfect sense.

It might be that jit-lock-defer-time already happens to work this
way.  If not, it probably should, and 0 instead of nil should be the
default value.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum