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Re: [ft-devel] Variable fonts: hhea/typo/win metrics interpreted differe

From: Behdad Esfahbod
Subject: Re: [ft-devel] Variable fonts: hhea/typo/win metrics interpreted differently for instances compared to static fonts?
Date: Thu, 20 Dec 2018 12:36:26 -0500

On Thu, Dec 20, 2018 at 5:32 AM Werner LEMBERG <address@hidden> wrote:

> I just tested the static and variable fonts in macOS 10.14 TextEdit.
> For the static instances, it presumably takes the hhea metrics, for
> the VF, it always takes typo metrics. (It also adds the line gap at
> the bottom, making text look weird, but maybe that's because the
> layout logic is broken.)

Thanks for testing!

> So that would speak in favor of always using either typo or win
> metrics for variable fonts, even for the default outlines?


Umm.  I suggest FreeType be changed to respect OS/2 useTypoMetrics bit.  This is my attempt in HB:

and then use same logic for VF and non-VF.  There's also the question of whether MVAR tags should apply to whatever was used for ascent/descent.  I think yes.  And I'll implement that in HB.

> Or maybe this is really the fault of GTK/Pango/something because it
> loads the default outline instead of the default instance, which
> would yield the correct metrics?

This is certainly the most convenient solution for me since I have
nothing to do on the FreeType side :-)

GTK/Pango/Cairo just call into FreeType for metrics.

I'm confused.  What does "default outline" vs "default instance" mean?
Your question, however, is a fundamental one: Shall a VF font be
always treated as VF, or is the `VFness' an optional feature?



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