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: Sat, 08 Oct 2016 15:18:26 -0400 [thread overview]
Message-ID: <87y41yved9.fsf@users.sourceforge.net> (raw)
In-Reply-To: <837f9ihg8l.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 08 Oct 2016 21:01:46 +0300")
Eli Zaretskii <eliz@gnu.org> writes:
>> From: npostavs@users.sourceforge.net
>> Cc: 24633@debbugs.gnu.org
>> Date: Sat, 08 Oct 2016 13:17:37 -0400
>>
>> The high-level idea is to have a line from going from the left to the
>> right edge of the window. Most of the line is composed of an overlay
>> specifying the :underline text property. The last bit of it, from the
>> end of the text to the right edge of the screen, is created by an
>> underlined after-string space which uses :align-to to reach the right
>> edge of the screen.
>>
>> Using :align-to 'right or :align-to `((,(window-body-width nil t))) does
>> not account for horizontal scrolling (i.e., the line ends at 80 columns,
>> even when the 80th column is scrolled to the left). So I tried
>>
>> `(+ ,(window-hscroll) (0 . right))
>> `(+ ,(window-hscroll) (,(window-body-width nil t))) ; initially this
>>
>> to make up for it, which turns out to cause this strange looping.
>
> 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.
I guess what I would expect is that the automatic hscrolling only goes
as far as the cursor is rendered, which should be the end of text where
I put the `cursor' property. If you think this would be too
complex/slow to implement, we can mark this bug as wontfix.
>
>> > 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?
next prev parent reply other threads:[~2016-10-08 19:18 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 [this message]
2016-10-08 19:57 ` Eli Zaretskii
2016-10-09 12:29 ` npostavs
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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