Re: [ft] CFF glyph height doubles with autohinting

[Derek B. Noonburg]

On 2014 Jan 24, Werner LEMBERG wrote:
> 
>> If I run "ftview 16 f1.cff", and then toggle autohinting on with the
>> 'f' key, the glyphs get taller.  Actually it doesn't seem to be 2x
>> -- closer to 1.5x taller.
>>
>> I believe the shorter height is correct.  I.e., the Adobe CFF engine
>> is getting it right, and the autohinter is getting it wrong.
> 
> The font is cheating: It incorrectly uses names like `A' or `p' for
> glyphs that are mathematical symbols.  Consequently, the auto-hinter
> believes that those glyphs are Latin characters and uses them to
> construct blue zones.  In particular, it distorts the x height to
> align it to the grid.

Ok, that makes sense.  For my particular application (rasterizing fonts
in a PDF view), I'm thinking maybe I should just disable autohinting
entirely.  Many PDF files use subsets, and the font handling abilities
of PDF generators are notoriously crappy.  I'm actually surprised I
haven't run into this kind of problem sooner.

Thanks for the feedback.

- Derek