From: John Yates <john@yates-sheets.org>
To: Eli Zaretskii <eliz@gnu.org>
Cc: Alan Mackenzie <acm@muc.de>, emacs-devel@gnu.org
Subject: Re: How can I predict which regions xdisp will present me for font-locking?
Date: Mon, 12 Mar 2012 13:47:00 -0400 [thread overview]
Message-ID: <CAJnXXoh+zcqHa9iZAAtGstVpKuEffgCiSwz+QGV0JhmgjZHTaA@mail.gmail.com> (raw)
In-Reply-To: <83d38iyfox.fsf@gnu.org>
On Sun, Mar 11, 2012 at 5:45 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>> Date: Sun, 11 Mar 2012 20:59:03 +0000
>> From: Alan Mackenzie <acm@muc.de>
>>
>> In a file.hpp, inside a 3355 line macro (I kid you not), I type a single
>> character. xdisp responds by presenting jit-lock, successively, with
>> four areas to fontify. (This was determined by
>> trace-function-background on `font-lock-fontify-region').
>>
>> None of these areas starts/stops at the top/bottom of the window. It is the
>> third area which encloses the changed line. The fourth area finishes
>> below the window's last line.
>>
>> I can't see how this wierd sequence of fontification areas can be
>> being calculated by CC Mode.
>>
>> This seemingly superfluous fontification seems to be causing a
>> performance degradation.
>>
>> How can this series of fontification regions be explained?
>
> I think what happens is this:
>
> . every change in the buffer triggers a call to
> font-lock-extend-jit-lock-region-after-change (via
> jit-lock-after-change-extend-region-functions)
>
> . font-lock-extend-jit-lock-region-after-change extends the region
> of the change according to the font-lock properties of the major
> mode, then marks that region unfontified by putting on it a
> `fontified' text property with the value nil
>
> . the next redisplay cycle calls jit-lock-function (via
> fontification-functions) at the beginning of the region whose
> `fontified' property is nil, and refontifies the region from there
> in chunks of 500 characters (but every chunk is extended so that
> its start is at the beginning of a line and its end is at the end
> of a line)
>
> Does this explain what you see?
How does this strategy differ from 23.x?
I am seeing a horrendous slowdown when editing atypical macros (though
no more than 50 lines long). Worse still I see the same slowdown when
editing a comment if even a fragment of my atypical macro is visible.
The pattern of the macro is
#define LIST_NAME \
_ROW_( <literal columns> ) \
, _ROW_( <literal columns> ) \
... \
, _ROW_( <literal columns> ) \
/john
next prev parent reply other threads:[~2012-03-12 17:47 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-11 20:59 How can I predict which regions xdisp will present me for font-locking? Alan Mackenzie
2012-03-11 21:45 ` Eli Zaretskii
2012-03-12 17:47 ` John Yates [this message]
2012-03-12 18:00 ` Eli Zaretskii
2012-03-13 19:50 ` John Yates
2012-03-13 21:00 ` Alan Mackenzie
2012-03-13 21:18 ` Eli Zaretskii
2012-03-12 18:49 ` Alan Mackenzie
2012-03-12 19:25 ` Stefan Monnier
2012-03-13 14:05 ` Alan Mackenzie
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