Created attachment 661993 [details]
example of xfce UI text with full hinting set

Upgraded to Leap 42.1 from an ISO DVD a few days ago without a problem.

Today (16th January), I did an online update and font hinting immediately broke
(without logging out or X restart).

Xfce's font control (Settings Manager->Appearance->Fonts) has some influence
over the rendering - the anti-aliasing switch works but the hinting styles
don't work as expected. AFAIK, full hinting should align the straight
horizontals/verticals to the pixel grid and ensure they're exactly 1px wide -
assuming the font has embedded hinting data.

It looks like the Settings Manager does much the same as the xfconf-query
command line utility;

Result of: xfconf-query -c xsettings -lv
/Gtk/CursorThemeName   DMZ
/Gtk/DecorationLayout  menu:minimize,maximize,close
/Gtk/FontName          Sans 11.5
/Net/DoubleClickTime   411
/Net/IconThemeName     oxygen
/Net/ThemeName         Adwaita
/Xfce/LastCustomDPI    96
/Xft/Antialias         1
/Xft/DPI               -1
/Xft/Hinting           -1
/Xft/HintStyle         hintfull
/Xft/RGBA              none

Example:
fonts_hinting_xfce_settings.png

There's hardly any visible difference between hintnone, hintfull and
hintmedium. Hintslight actually makes some fonts look the cleanest/sharpest,
e.g. terminal text (Monospace 10pt) but has less effect with fonts elsewhere.
None of the settings cleanly align the font verticals/horizontals to the pixel
grid. See attachments:

fonts_hinting_terminal_hintnone.png
fonts_hinting_terminal_hintslight.png
fonts_hinting_terminal_hintmedium.png
fonts_hinting_terminal_hintfull.png

Tried a number of alternative system fonts but they all have much the same
rendering issue.

Also looked at Yast2->Font Configuration
the default settings were (iirc):
Font Antialiasing (enabled)
Force Autohinting On (disabled)
Force Hint Style (none)

These settings didn't seem to have any effect outside the yast utility. Also,
'hintfull' had the same problem as with xfconf-query - that is, not fully
hinted. See:
fonts_hinting_yast2_font_setting_hintfull.png