Subject: 25.2; font issue with FreeType 2.8; should not use the rounded ascender and descender

From: Vincent Lefevre <[email-masked]>
Date: Tue, 31 Oct 2017 11:12:47 +0100

For TrueType fonts, FreeType 2.8 uses different rounding rules for
values in the FT_Size_Metrics structure, which is apparently used
by Emacs (since there are visible changes). In particular, one can
now have ascender + descender > height. The consequences are:

1. Tables look a bit ugly.

2. Windows (with the same number of text lines) are unnecessarily
   higher than before.

3. This can break existing configurations, where Emacs would be
   opened at start up, with an expected window size.

I could notice changes at least with the default Mono font, which
appears to be DejaVu Sans Mono.

Upstream now recommends to use the values from the FT_Face structure
and scale them manually:

------------------------------------------------------------------------

Global size metrics values in the `FT_Size_Metrics' structure can be
different for TrueType fonts. Reason is that in older FreeType
versions the metrics were rounded differently to integer pixels
compared to all other font formats, yielding an inconsistent behaviour
if you used non-native hinting. Starting with this version, global
size metrics for TrueType fonts are handled the same as other font
formats: `ascender' gets rounded up, `descender' getsrounded down,
`height' gets normally rounded, and `max_advance' gets normally
rounded, too.

If you need more precise values of (global) ascender, descender,
height, or `max_advance', please take the corresponding values from
the `FT_Face' structure and scale them manually.

------------------------------------------------------------------------

See the discussion:
  https://savannah.nongnu.org/bugs/?52165

In GNU Emacs 25.2.2 (x86_64-pc-linux-gnu, GTK+ Version 3.22.20)
 of 2017-09-12, modified by Debian built on trouble
Windowing system distributor 'The X.Org Foundation', version 11.0.11905000
System Description:	Debian GNU/Linux stable-updates (sid)

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Recent messages:
Loading /etc/emacs/site-start.d/50latex-cjk-common.el (source)...done
Loading /etc/emacs/site-start.d/50latex-cjk-thai.el (source)...done
Loading /etc/emacs/site-start.d/50psvn.el (source)...done
Loading /etc/emacs/site-start.d/50rnc-mode.el (source)...done
Loading /etc/emacs/site-start.d/50texlive-lang-english.el (source)...done
Loading /etc/emacs/site-start.d/50w3m-el.el (source)...done
Loading /home/vlefevre/share/emacs/site-lisp/mutteditor.el (source)...done
Loading time...done
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...

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