bug#35781: Discrepancies between xftfont.c and ftcrfont.c

[Kévin Le Gouguec]

retitle 35781 Make Cairo build obey hint-style font setting
thanks

I am nowhere close to a proper fix, but at least I think I am starting
to get a clearer picture of the situation.

The distribution installed on my laptop sets the "hint-style" font
setting to "slight" in both ~/.config/fontconfig/fonts.conf and
~/.Xresources.  AFAICU fontconfig and X resources are two (competing?)
mechanisms that tell graphical applications what fonts and font
settings they should use.  OK.

I am still studying the lay of the land; I see that xftfont_open in
xftfont.c calls xftfont_add_rendering_parameters, which has a bunch of
hint-style-related code calling fontconfig functions, while
ftcrfont_open in ftcrfont.c seems blissfully unaware of fontconfig.

At this point I am assuming that only ftcrfont.c is used in Cairo
builds, since config.h does not define HAVE_XFT, but my knowledge of
font management in Emacs is pretty lacking so I will have to check this
assumption.

As I said, I am far from being able to cook up any sort of patch at
this point; I still intend to keep digging Soonish™, but since that
may take a while, I figured I would update this report with whatever
information I gathered this far for posterity.