bug#42240: Interpretation of 'size' Property in Fontconfig Pattern Strings

bug#42240: Interpretation of 'size' Property in Fontconfig Pattern Strings

[Sebastian Miele]

GNU Emacs 27.0.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20)
of 2020-06-28

According to 'man 5 fonts-conf' the Fontconfig property 'size' is a
double and represents the point size. The property 'pixelsize', too, is
a double and represents the pixel size.

In

  FC_DEBUG=1 emacs -Q --font=:family=Hack:size=11

the 'size=11' is interpreted as 'pixelsize=11'.

  fc-match :family=Hack:size=11 size pixelsize

does interpret it as point size.

Apart from that both

  emacs -Q --font=:family=Hack:size=11.1

and

  emacs -Q --font=:family=Hack:pixelsize=11.1

both yield the same error: "invalid font property: (:size . 11\.1)",
although according to fontconfig the pixel size is a double, too.
However, fractional pixel sizes may not make sense for Emacs at all. I
do not know.

The following does work as expected:

  emacs -Q --font=Hack-11.1

bug#42240: Interpretation of 'size' Property in Fontconfig Pattern Strings

[Robert Pluim]

>>>>> On Tue, 07 Jul 2020 13:25:15 +0200, Sebastian Miele <sebastian.miele@gmail.com> said:

    Sebastian> GNU Emacs 27.0.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20)
    Sebastian> of 2020-06-28

    Sebastian> According to 'man 5 fonts-conf' the Fontconfig property 'size' is a
    Sebastian> double and represents the point size. The property 'pixelsize', too, is
    Sebastian> a double and represents the pixel size.

Is this a build with or without Cairo? (you snipped the part of the
bug report that would have told us)

    Sebastian> In

    Sebastian>   FC_DEBUG=1 emacs -Q --font=:family=Hack:size=11

    Sebastian> the 'size=11' is interpreted as 'pixelsize=11'.

    Sebastian>   fc-match :family=Hack:size=11 size pixelsize

    Sebastian> does interpret it as point size.

    Sebastian> Apart from that both

    Sebastian>   emacs -Q --font=:family=Hack:size=11.1

    Sebastian> and

    Sebastian>   emacs -Q --font=:family=Hack:pixelsize=11.1

    Sebastian> both yield the same error: "invalid font property: (:size . 11\.1)",
    Sebastian> although according to fontconfig the pixel size is a double, too.
    Sebastian> However, fractional pixel sizes may not make sense for Emacs at all. I
    Sebastian> do not know.

    Sebastian> The following does work as expected:

    Sebastian>   emacs -Q --font=Hack-11.1

bug#42240: Interpretation of 'size' Property in Fontconfig Pattern Strings

[Sebastian Miele]

Robert Pluim <rpluim@gmail.com> writes:

> Is this a build with or without Cairo? (you snipped the part of the
> bug report that would have told us)

Both issues described happen both with and without cairo (both checked
out from the emacs-27.0.91 tag). Here is the complete information of
`report-emacs-bug' of the build without cairo:

In GNU Emacs 27.0.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20)
 of 2020-06-28 built on huette
Repository revision: c36c5a3dedbb2e0349be1b6c3b7567ea7b594f1c
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Arch Linux

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...

Configured using:
 'configure --with-x-toolkit=gtk3 --with-mailutils'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND GPM DBUS GSETTINGS GLIB NOTIFY INOTIFY
ACL GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD JSON
PDUMPER LCMS2 GMP

Important settings:
  value of $LC_CTYPE: de_DE.UTF-8
  value of $LANG: C
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-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
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search time-date
subr-x seq byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core term/tty-colors frame minibuffer 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 composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
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 threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 44887 6437)
 (symbols 48 6007 1)
 (strings 32 15413 1544)
 (string-bytes 1 501852)
 (vectors 16 10087)
 (vector-slots 8 129959 12406)
 (floats 8 20 33)
 (intervals 56 197 0)
 (buffers 1000 12))

bug#42240: Interpretation of 'size' Property in Fontconfig Pattern Strings

[Sebastian Miele]

Sebastian Miele <sebastian.miele@gmail.com>:

> Robert Pluim <rpluim@gmail.com>:
>
>> Is this a build with or without Cairo? (you snipped the part of the
>> bug report that would have told us)
>
> Both issues described happen both with and without cairo (both checked
> out from the emacs-27.0.91 tag). Here is the complete information of
> `report-emacs-bug' of the build without cairo:
>
> [..]

The build without cairo also contained '--without-xft' (although I do
not really know the consequences). Here is the complete
`report-emacs-bug' info from that build:

In GNU Emacs 27.0.91 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.21, cairo version 1.17.3)
 of 2020-07-06 built on huette
Repository revision: c36c5a3dedbb2e0349be1b6c3b7567ea7b594f1c
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Arch Linux

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --with-x-toolkit=gtk3 --with-mailutils --with-cairo
 --without-xft'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD JSON
PDUMPER LCMS2 GMP

Important settings:
  value of $LC_CTYPE: de_DE.UTF-8
  value of $LANG: C
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-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
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search time-date
subr-x seq byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel term/x-win x-win term/common-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
timer select scroll-bar mouse jit-lock font-lock syntax facemenu
font-core term/tty-colors frame minibuffer 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 composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray
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 threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
cairo move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 44842 6073)
 (symbols 48 6005 1)
 (strings 32 15430 1775)
 (string-bytes 1 504623)
 (vectors 16 10098)
 (vector-slots 8 130183 10652)
 (floats 8 19 39)
 (intervals 56 190 0)
 (buffers 1000 11))

bug#42240: Interpretation of 'size' Property in Fontconfig Pattern Strings

[Robert Pluim]

>>>>> On Thu, 16 Jul 2020 18:07:50 +0200, Sebastian Miele <sebastian.miele@gmail.com> said:

    Sebastian> Sebastian Miele <sebastian.miele@gmail.com>:
    >> Robert Pluim <rpluim@gmail.com>:
    >> 
    >>> Is this a build with or without Cairo? (you snipped the part of the
    >>> bug report that would have told us)
    >> 
    >> Both issues described happen both with and without cairo (both checked
    >> out from the emacs-27.0.91 tag). Here is the complete information of
    >> `report-emacs-bug' of the build without cairo:
    >> 
    >> [..]

    Sebastian> The build without cairo also contained '--without-xft' (although I do
    Sebastian> not really know the consequences). Here is the complete
    Sebastian> `report-emacs-bug' info from that build:

Cairo implies --without-xft in any case, so no harm done. Looks like
Iʼll have to boot up my GNU/Linux box (although Iʼm hazy on the
difference between 'size' and 'pixelsize')

Robert

bug#42240: Interpretation of 'size' Property in Fontconfig Pattern Strings

[Sebastian Miele]

Robert Pluim <rpluim@gmail.com>:

> Cairo implies --without-xft in any case, so no harm done.

Good to know. Thank you.

> Looks like Iʼll have to boot up my GNU/Linux box (although Iʼm hazy on
> the difference between 'size' and 'pixelsize')

The main Fontconfig manual page describing all properties is called 'man
5 fonts-conf' (which can be hard to find, because neither 'fc' nor
'fontconfig' are substrings of 'fonts-conf').

The 'size' is the point size. In general, there are many different
definitions of point size. But in practice only one is used nowadays
(except by TeX which uses a slightly different but very close definition
that works better with its fixed point arithmetics). Usually a point is
1/72 inch (https://en.wikipedia.org/wiki/Point_(typography)).

Together with 'dpi' (dots/pixels per inch) that defines the relation
between point size and pixel size.

X has at least two different places where a dpi may be defined. One for
the entire X display, although that does not really make sense with an X
display having monitors of different pixel densities. Apart from that at
least the Xrandr extension has a notion of distinct dpis per monitor.

In general, Fontconfig has an even separate dpi. I do not really know
what dpi Fontconfig uses, if it is not explicitly set in the Fontconfig
configuration, but, e.g.,

  fc-match :family=Hack:size=11.1 size pixelsize dpi

or

  fc-match -v :family=Hack:size=11.

display the dpi used.

bug#42240: Interpretation of 'size' Property in Fontconfig Pattern Strings

[Sebastian Miele]

I have just built a fresh Emacs with cairo from the emacs-27 branch
(commit d24e56a5e4959f82b3da0dfac9ee3c428e077cbd). The two issues are
present there, too.