bug#29078: 25.2; font issue with FreeType 2.8; should not use the rounded ascender and descender

[Vincent Lefevre]

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)

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.2/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --build x86_64-linux-gnu
 --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.2/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-x=yes --with-x-toolkit=gtk3
 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs25-XrMyQe/emacs25-25.2+1=.
 -fstack-protector-strong -Wformat -Werror=format-security -Wall'
 'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LC_COLLATE: POSIX
  value of $LC_CTYPE: en_US.UTF-8
  value of $LC_TIME: en_DK
  value of $LANG: POSIX
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  display-time-mode: t
  show-paren-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

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...

Load-path shadows:
/usr/share/emacs25/site-lisp/cmake-data/cmake-mode hides 
/usr/share/emacs/site-lisp/cmake-mode
/usr/share/emacs/25.2/site-lisp/debian-startup hides 
/usr/share/emacs/site-lisp/debian-startup
/usr/share/emacs25/site-lisp/flim/md4 hides /usr/share/emacs/25.2/lisp/md4
/usr/share/emacs25/site-lisp/flim/hex-util hides 
/usr/share/emacs/25.2/lisp/hex-util
/usr/share/emacs25/site-lisp/flim/sasl-cram hides 
/usr/share/emacs/25.2/lisp/net/sasl-cram
/usr/share/emacs25/site-lisp/flim/hmac-md5 hides 
/usr/share/emacs/25.2/lisp/net/hmac-md5
/usr/share/emacs25/site-lisp/flim/hmac-def hides 
/usr/share/emacs/25.2/lisp/net/hmac-def
/usr/share/emacs25/site-lisp/flim/sasl-digest hides 
/usr/share/emacs/25.2/lisp/net/sasl-digest
/usr/share/emacs25/site-lisp/flim/sasl hides /usr/share/emacs/25.2/lisp/net/sasl
/usr/share/emacs25/site-lisp/flim/sasl-ntlm hides 
/usr/share/emacs/25.2/lisp/net/sasl-ntlm
/usr/share/emacs25/site-lisp/flim/ntlm hides /usr/share/emacs/25.2/lisp/net/ntlm
/usr/share/emacs25/site-lisp/latex-cjk-thai/thai-word hides 
/usr/share/emacs/25.2/lisp/language/thai-word

Features:
(shadow sort mail-extr warnings emacsbug message dired format-spec
rfc822 mml mml-sec password-cache epg epg-config gnus-util mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums mm-util help-fns help-mode easymenu
mail-prsvr mail-utils time cus-start cus-load paren cc-styles cc-align
cc-engine cc-vars cc-defs edmacro kmacro cl-loaddefs pcase cl-lib
w3m-load time-date mule-util tooltip eldoc electric uniquify ediff-hook
vc-hooks lisp-float-type mwheel x-win term/common-win x-dnd tool-bar dnd
fontset image regexp-opt fringe tabulated-list newcomment elisp-mode
lisp-mode prog-mode register page menu-bar rfn-eshadow timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core frame
cl-generic cham georgian utf-8-lang misc-lang vietnamese tibetan thai
tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek romanian
slovak czech european ethiopic indian cyrillic chinese charscript
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote dbusbind inotify
dynamic-setting system-font-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 107514 7364)
 (symbols 48 22500 0)
 (miscs 40 55 113)
 (strings 32 20823 4597)
 (string-bytes 1 613432)
 (vectors 16 12942)
 (vector-slots 8 444085 4241)
 (floats 8 171 38)
 (intervals 56 277 12)
 (buffers 976 19))