[Fontconfig] FreeType now includes Infinality subpixel support

Infinality
Wed, 20 Jun 2012 20:11:03 -0000

On 06/20/2012 02:19 AM, Akira TAGOH wrote:
> Hi,
>
> One concern on this matter is how it affects to the visibility when
> mixing up the fonts with/without ClearType bytecode. I may be wrong
> because I''m not checking that myself. but just heard one get tired
> easily to keep looking in that situation. dunno.

As far as I know, there really isn''t bytecode that is specific to
Cleartype.  Bytecode is bytecode.  The Cleartype flag (or the phrase
"designed for Cleartype") generally means that the font
doesn''t contain
the legacy hacks used in fonts like Arial, Courier New, etc., which are
problematic when being displayed with antialiasing on a TT rasterizer
that is following specs.  The subpixel hinting functionality works
around the issues with the legacy fonts, while allowing modern fonts to
render as though they are "designed for Cleartype".   Or am I not
understanding what you mean here?

>
> Other than that, it may be useful for buggy fonts.
>
> As Windows still has an option to turn off (right?),

The choices you get in Windows (as far as I know) are to have Cleartype
on or off.  In fontconfig this would correspond to the below
configurations.  A link to a corresponding image is above each
configuration.  (Don''t pay attention to the text in it, because
it''s the
same across all images):

http://www.infinality.net/images/cleartype-on.png

         <match target="font">
                 <edit name="rgba" mode="assign">
                         <const>rgb</const>
                 </edit>
                 <edit name="hinting" mode="assign">
                         <bool>true</bool>
                 </edit>
                 <edit name="autohint" mode="assign">
                         <bool>false</bool>
                 </edit>
                 <edit name="antialias" mode="assign">
                         <bool>true</bool>
                 </edit>
                 <edit name="hintstyle" mode="assign">
                         <const>hintfull</const>
                 </edit>
         </match>

http://www.infinality.net/images/cleartype-off.png

         <match target="font">
                 <edit name="rgba" mode="assign">
                         <const>none</const>
                 </edit>
                 <edit name="hinting" mode="assign">
                         <bool>true</bool>
                 </edit>
                 <edit name="autohint" mode="assign">
                         <bool>false</bool>
                 </edit>
                 <edit name="antialias" mode="assign">
                         <bool>false</bool>
                 </edit>
                 <edit name="hintstyle" mode="assign">
                         <const>hintfull</const>
                 </edit>
         </match>

Since the subpixel hinting is automatically set to be off whenever
FT_RENDER_MODE_MONO (i.e. antialias=false) is requested, no additional
fontconfig configuration would be required to turn "Cleartype" off.
That way you can still get the default Windows XP look, where Cleartype
is off, and it renders MONO, but still uses the native TT hinter.  If
you want Cleartype on, you just set antialias=true.  What you don''t get
anymore is antialiasing with the native TT rendering:

http://www.infinality.net/images/aa-native-tt.png

If you look at the Times New Roman "2, 3", Arial  "r, g, b, e,
O" (12px
to 17px) and others, you can see artifacts ranging from vanishing stems
to dents in the outline.  This is because these particular fonts were
never designed to render with both antialiasing and TT hinting.  So, my
argument is that this form of rendering is wrong, was never intended,
and shouldn''t be accommodated into fontconfig rules.  But, like I said,
some people may have gotten used to this rendering, as incorrect and
wrong as it is, and will be upset if it isn''t possible to do this
anymore.  Of course, it is possible if you don''t compile Freetype with
subpixel hinting enabled.  So, I figure that minority of people can
still have their way if they want to.

Sorry for the long explanation, but as you know, stuff related to fonts
is always more complex than you''d link at first glance.  ;)

Erik