Re: [ft] iOS 7 system font Helvetica Neue horribly mis-hinted with FreeType 2.5.3

[Louis Semprini]

> Date: Wed, 13 Aug 2014 16:27:47 +0200
> To: address@hidden
> CC: address@hidden
> Subject: Re: [ft] iOS 7 system font Helvetica Neue horribly mis-hinted with FreeType 2.5.3
> From: address@hidden
>
>
> > I have some absolutely minimal FreeType code that just tries to
> > render simple A-Z glyphs with the iOS system font, "Helvetica Neue
> > Interface."
> >
> > I am seeing FT results that are horribly disfigured like the
> > attached file bad_hinting.png or you can see the same image here:
> >
> > http://postimg.org/image/dplczjbeb/
>
> Hinting? AFAIK, Apple platforms don't do hinting at all.
>
> > As you can see, random character strokes are thick and random
> > strokes are thin, as if FT were trying to fit my text to some coarse
> > grid.
>
> To check whether there is a problem with the hinting as done with
> FreeType, you should copy the font to a Windows platform and compare
> the results.
>
> Looking at the first font in the TTC with ftview, I get decent results
> if I activate subpixel hinting.

Just an update for those folks on the freetype mailing list who are having the same problem.

We did some more experiments including rendering the same font on Windows (e.g. in Notepad; the Apple iOS fonts cannot be installed on Windows directly so this test required extracting the first .ttf from the .ttc and re-generating the .ttf using FontForge).

Windows was able to render the font without the same major artifacts shown in the first email attachment (though Windows didn't antialias as well as FreeType).  When we render the extracted .ttf font using the same FreeType code as the .ttc, we still get the major artifacts.

When Werner says "activate subpixel hinting," he means recompile FreeType with the following experimental option uncommented in ftoption.h:

#define TT_CONFIG_OPTION_SUBPIXEL_HINTING

when compiled this way, FreeType can render the Apple font OK without artifacts.

So the conclusion so far is that FreeType may have a bug that shows up with the Apple iOS system font when TT_CONFIG_OPTION_SUBPIXEL_HINTING is not defined, but that TT_CONFIG_OPTION_SUBPIXEL_HINTING is a workaround for now.

Werner, can you comment more about the description of that option as "experimental?"  Should we be wary of using TT_CONFIG_OPTION_SUBPIXEL_HINTING in production code?  If so, any ideas about how to fix the font in the non-TT_CONFIG_OPTION_SUBPIXEL_HINTING code base?

Thanks for your awesome library!