Re: [ft-devel] Hinting paths

[Werner LEMBERG]

>> [...]  a font *can* circumvent this limitation by activating
>> `native ClearType hinting' (selector index 3 of the INSTCTRL
>> instruction; this works since FreeType version 2.6).  In this mode,
>> there are no backwards-compatibility restrictions, and you can
>> happily emit horizontal hints in ClearType.
> 
> Ah, so native ClearType hinting works now, just not
> backwards-compatible ClearType hinting for older fonts?

Native ClearType hinting is *completely identical* to normal TrueType
hinting.  It's just a flag that says `Please switch off the
backwards-compatible hacks.  I know how to hint properly for
ClearType.'

One peculiarity to note: If in `native ClearType' mode, a modification
of a glyph's advance width is properly executed by the MS hinter.
However, the MS rasterizer ignores it, always using linear advance
widths in modern Windows versions.  Previous versions supported a
`compatible-width ClearType' mode (cf. selector bit 7 in the GETINFO
instruction).  Unfortunately, there is no way currently to circumvent
this.

> And the latter is needed to fully handle ClearType?

Yes.  Backwards-compatibility mode is essential to hint older fonts,
or fonts that are written to use the same bytecode for both ClearType
and non-ClearType, relying on the fact that (most) instructions along
the horizontal axis are ignored.

>> What do you mean with `stronger X-and-Y-fitting'?  FreeType's
>> auto-hinter only supports two modes: `normal' and `light'.
> 
> I found rendering differences between autohint on and
> hintmedium/full that were different from autohint off and
> hintmedium/full.

Example, please, ideally translated to key sequences that I can use
with ftview.


    Werner