[gnome-settings-daemon] xsettings: Change font hinting to default to 'slight'

[Bastien Nocera <hadess src gnome org>]

commit e2926353e471955e8e684264e826da5b8643e83e
Author: Nikolaus Waxweiler <madigens gmail com>
Date:   Wed Oct 7 22:22:08 2015 +0200

    xsettings: Change font hinting to default to 'slight'
    
    The current default of "medium" is problematic because "medium"
    and "full" are coarse descriptions that mean different things to
    different font formats. This leads to widely inconsistent font rendering
    and mishandling of popular (TrueType) fonts.
    
    First, there are 2 major ways to make fonts readable on low-DPI screens:
    - X-and-Y-fitting, as done on Windows for a long time before ClearType
      and DirectWrite. Glyph outlines are shuffled about (read: distorted) to
      fit them to the pixel grid. The goal is maximum sharpness at the
      expense of outline fidelity and glyph spacing.
    - Y-only-fitting: Done by ClearType, DirectWrite and Adobe's proprietary
      font rendering engine to exploit the RGB-subpixel-stripe configuration
      of modern LCDs. Outlines are only fitted to the Y-axis, so the
      rasterizer can use tricks ("subpixel rendering") on the X-axis to
      enhance contrast or perceived resolution. Since horizontal (X-axis)
      metrics are unchanged, glyph spacing stays as is.
    
    The higher the resolution (as in DPI) of a screen, the less important
    hinting/grid-fitting becomes.
    
    With the fontconfig property "autohint" set to false:
    - FreeType's TrueType (.ttf) engine will use the native hinting bytecode
      in the font.  Depending on how much effort went into hinting the font
      and whether it was optimized for ClearType, glyphs might be
      grid-fitted to X-and-Y-axis or Y-axis only.  ClearType is not yet
      fully handled by FreeType (2.6.1), so popular fonts from the Windows
      world will be more or less distorted. "Medium" seems to be a variant
      of "full".
    - the OpenType/CFF engine uses a different approach to rendering for
      low-DPI screens. Font designers of Type 1/CFF fonts just specify
      metadata that tell the hinting engine how to fit glyphs to the Y-axis
      (no X-fitting!), so the details of grid-fitting are deferred to the
      smarts of the hinting engine. "Medium" is equivalent to "full" here.
    - The Postscript/Type 1 engine is the predecessor to the CFF engine in
      spirit. Hinting works as with CFF. The Type 1 engine in FreeType is
      older than Adobe's contributed CFF engine and hinting results are of
      far lower quality. "Medium" is mostly "Full".
    - "Slight" will always trigger the autohinter regardless of font format.
      Y-fitting only.
    
    Since the computer world is comprised of more than one typeface and more
    than one font format, users will see jarringly inconsistent and
    distorted fonts with "medium" and "full" due to the differences in the
    engines and inconsistent quality of many typefaces in the wild.  The
    problem is nicely visible when you go medium or full and mix font
    formats.  A default installation of Fedora will have Cantarell in
    OpenType/CFF (.otf) format in the UI and DejaVu (.ttf) on the console.
    Cantarell is Y-fitted (and slightly emboldened), DejaVu X-and-Y-fitted.
    The difference is jarring.
    
    With the fontconfig property "autohint" set to true, FreeType's
    autohinter is triggered and native hinting disabled. "Slight" will fit
    to the Y-axis only, "medium" and "full" fit to X-and-Y-axes with
    differing strength and usually lower quality.
    
    From my testing, anything other than the autohinter on "slight" and the
    native CFF engine on "medium" or "full" will lead to inconsistent
    rendering and distortion. I recommend "slight" because the autohinter
    does a good and consistent job regardless of font format, the maintainer
    is also adding support for more scripts. Ubuntu has been using it for
    years.
    
    The future will soon bring high-DPI screens for the
    masses, and that's where Y-only-fitting as done by the slight autohinter
    and the CFF engine shines. Glyphs are rendered *much* cleaner and
    inter-glyph-spacing remains untouched. A lot of native hinting done on
    TrueType fonts, especially the X-and-Y variant, was made with low-DPI
    screens in mind and can look bad when applied on high-DPI screens.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=756204

 ...ings-daemon.plugins.xsettings.gschema.xml.in.in |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/data/org.gnome.settings-daemon.plugins.xsettings.gschema.xml.in.in 
b/data/org.gnome.settings-daemon.plugins.xsettings.gschema.xml.in.in
index 0687b05..0e6700c 100644
--- a/data/org.gnome.settings-daemon.plugins.xsettings.gschema.xml.in.in
+++ b/data/org.gnome.settings-daemon.plugins.xsettings.gschema.xml.in.in
@@ -11,9 +11,9 @@
       <_description>The type of antialiasing to use when rendering fonts. Possible values are: "none" for no 
antialiasing, "grayscale" for standard grayscale antialiasing, and "rgba" for subpixel antialiasing (LCD 
screens only).</_description>
     </key>
     <key name="hinting" enum="org.gnome.settings-daemon.GsdFontHinting">
-      <default>'medium'</default>
+      <default>'slight'</default>
       <_summary>Hinting</_summary>
-      <_description>The type of hinting to use when rendering fonts. Possible values are: "none" for no 
hinting, "slight" for basic, "medium" for moderate, and "full" for maximum hinting (may cause distortion of 
letter forms).</_description>
+      <_description>The type of hinting to use when rendering fonts. Possible values are: "none" for no 
hinting and "slight" for fitting only to the Y-axis like Microsoft's ClearType, DirectWrite and Adobe's 
proprietary font rendering engine. Ignores native hinting within the font, generates hints algorithmically. 
Used on Ubuntu by default. Recommended. The meaning of "medium" and "full" depends on the font format (.ttf, 
.otf, .pfa/.pfb) and the installed version of FreeType. They usually try to fit glyphs to both the X and the 
Y axis (except for .otf: Y-only). This can lead to distortion and/or inconsistent rendering depending on the 
quality of the font, the font format and the state of FreeType's font engines.</_description>
     </key>
     <key name="priority" type="i">
       <default>0</default>