From: npostavs@users.sourceforge.net
To: Eli Zaretskii <eliz@gnu.org>
Cc: 24633@debbugs.gnu.org
Subject: bug#24633: highlight-region func using (window-hscroll) in :align-to spec can cause inf loop
Date: Sun, 09 Oct 2016 08:29:51 -0400 [thread overview]
Message-ID: <87lgxxvh6o.fsf@users.sourceforge.net> (raw)
In-Reply-To: <83y41yfwam.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 08 Oct 2016 22:57:53 +0300")
Eli Zaretskii <eliz@gnu.org> writes:
>> From: npostavs@users.sourceforge.net
>> Cc: 24633@debbugs.gnu.org
>> Date: Sat, 08 Oct 2016 15:18:26 -0400
>>
>> > Automatic hscrolling is based on length of point's line at the end of
>> > redisplaying a window. Here, "line length" means the horizontal space
>> > required for displaying all the glyphs of the line, which includes the
>> > glyphs that come from the after-string. Since you extend your
>> > after-string each time the window is hscrolled, you in effect enlarge
>> > the line each time the display engine hscrolls the window, which
>> > causes an endless loop.
>> >
>> > Can you restrict the after-string's length so it always ends at the
>> > last character of the line, or some fixed number of columns afterward?
>>
>> Then it won't reach the edge of the screen when the buffer is scrolled.
>
> Yes, but is it so bad?
Hmm, it's not quite the effect I was going for, but actually maybe it
isn't that bad.
> It'd be messy, yes. We'd need to search for before- and after-strings
> that begin/end right at point, then augment the call to the display
> emulating function accordingly, deal with complications like strings
> that include newlines, etc.
Anyway, it doesn't seem worth going through this complexity. I just
wonder if there is some way to stop bad lisp code from triggering a hard
lockup. Can the display engine notice if it's looping and throw some
kind of error? Maybe unset pre-redisplay-functions?
>
>> >> > In particular, I don't
>> >> > understand the align-to expression: e.g., window-hscroll returns its
>> >> > value in columns, while align-to needs pixels, AFAIU.
>> >>
>> >> According to `(elisp) Pixel Specification',
>> >>
>> >> The form NUM specifies a fraction of the default frame font height
>> >> or width. The form `(NUM)' specifies an absolute number of pixels.
>> >
>> > I admire your courage in reading that documentation and then writing
>> > stuff like the above, which the documentation doesn't mention even
>> > remotely.
>>
>> Uh, not sure how to read this, is it irony?
>
> Only a little. I find this area severely under-documented.
The grammar in the doc seems complete to me. Although using "fraction
of" to mean "gets multiplied by" is perhaps a bit unintuitive.
next prev parent reply other threads:[~2016-10-09 12:29 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-07 1:01 bug#24633: highlight-region func using (window-hscroll) in :align-to spec can cause inf loop npostavs
2016-10-08 11:15 ` Eli Zaretskii
2016-10-08 17:17 ` npostavs
2016-10-08 18:01 ` Eli Zaretskii
2016-10-08 19:18 ` npostavs
2016-10-08 19:57 ` Eli Zaretskii
2016-10-09 12:29 ` npostavs [this message]
2016-10-09 12:42 ` Eli Zaretskii
2016-10-22 19:27 ` npostavs
2016-10-22 19:41 ` Eli Zaretskii
2016-10-22 20:43 ` npostavs
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