bug#35079: 26.1; Font rendering - problem with bdf fonts

[Eli Zaretskii <eliz@gnu.org>]

> From: handa.kenichi@aist.go.jp (K.Handa)
> Cc: xsrvmy@gmail.com, 35079@debbugs.gnu.org, handa@gnu.org
> Date: Sat, 13 Apr 2019 19:35:55 +0900
> 
> For this, I found that fontconfig gives 'spacing' parameter of that font
> as FC_CHARCELL.  I think the spacing of that font should be FC_DUAL.
> Anyway, src/xftfont.c of Emacs does not know about FC_CHARCELL.  So,
> emacs treats that font as a mono-space font.
> 
> I think you can modify the spacing paramter of that font to FC_DUAL by
> writing some code in ~/.fonts.conf.
> 
> Or, please try to apply this patch to src/xftfont.c, and rebuild emacs.

Should I install this change now?  Can it do any harm?

> I don't know the exact meaning of FC_CHARCELL.  I could't find it on the
> Internet.  Does anyone know what it means and why fontconfig uses it for
> the gnu unifont?

I found this in
https://github.com/freedesktop/xorg-libXft/blob/master/NEWS:

  Version 2.1.7

  Change FC_CHARCELL and FC_MONO interpretation.  FC_MONO no longer clips
  glyphs to charcell, you must specify FC_CHARCELL for that.

But I guess you saw this too?  It sounds like FC_CHARCELL is the same
as monospaced, but with clipping to character cell, whatever that may
mean.

Thanks.