GNU bug report logs - #20510
25.0.50; Underscore hidden by underline

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From: Stefan Kangas <stefan <at> marxist.se>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Fabrice Niessen <fni-news <at> pirilampo.org>, 20510 <at> debbugs.gnu.org
Subject: bug#20510: 25.0.50; Underscore hidden by underline
Date: Mon, 30 Sep 2019 02:10:24 +0200

tags 20510 + wontfix
close 20510
thanks

Eli Zaretskii <eliz <at> gnu.org> writes:

>> From: Fabrice Niessen <fni-news <at> pirilampo.org>
>> Cc: 20510 <at> debbugs.gnu.org
>> Date: Wed, 06 May 2015 21:00:16 +0200
>>
>> I mean: can't the hl-line-mode code be written in a way that the
>> underline goes in the background of the character, that is that every
>> pixel of every character gets written "over" the underline line?
>
> hl-line-mode cannot control that, and nothing on the Lisp level can.
>
> When hl-line-mode puts its overlay on a line, the characters of that
> line have the hl-line face merged with their face, with the result
> that each character of that line will have the underline face in the
> color you specify.  That's all Lisp can do; then along comes the
> display engine and redraws the characters in this new merged face.
> The C code which draws characters is written so that we first draw the
> background, then the characters, then the underline.
>
> So what you are actually asking is that the order of drawing the
> underline (and also overline, strike-through, etc.) is changed so that
> these attributes are drawn _before_ the characters.  That should be
> possible by changing the order in the C code, but I have no idea what
> that will do in other situations.  It's probably not TRT at least when
> we draw images and other similar stuff instead of characters.
>
> Perhaps someone who knows more than I do about GUI display back-end
> could tell if this is a safe change.

It sounds to me like this is not something we are interested in doing.
I'm closing this as wontfix.

Please reopen if I'm mistaken.

Best regards,
Stefan Kangas

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