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Re: How can I predict which regions xdisp will present me for font-locki
Re: How can I predict which regions xdisp will present me for font-locking?
Sun, 11 Mar 2012 23:45:50 +0200
> Date: Sun, 11 Mar 2012 20:59:03 +0000
> From: Alan Mackenzie <address@hidden>
> 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 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?
Re: How can I predict which regions xdisp will present me for font-locking?, Stefan Monnier, 2012/03/12