[mpeg-OTspec] CFR ascender and descender

[Denis Jacquerye]

Would it make sense to propose having script or language system specific
Ascender/Descender or Max/Min in CFR?
One might want to have script specific or language specific line heights
when compositing from multiple fonts. Whether these metrics are from the
BASE table Max/Min or another source is an issue that needs to be clarified
in OFF.

Cheers,
On 19 Nov 2013 19:02, "John Hudson" <john at tiro.ca> wrote:

> Vladimir wrote:
>
> > I am not sure if using OS/2 sTypo... values would be a good choice
> > because in the majority of fonts the actual values recorded in those
> > fields can't really be trusted.
>
> Also, the sTypoAscender and -Descender values are expected to be used in
> concert with the sTypoLinegap value, and without that third piece of
> information they are useless.
>
> > In particular, I would suggest to at least consider the following
> strategy:
> > - if the CFR <FontMetrics> element defines ascender and descender values
> > - the implementation will use the values defined by a CFR author;
>
> Perhaps we also need to look more closely at what it means to 'use'
> those metrics, in terms of the distinction that OS/2 metrics have at
> least tried to make between linespacing metrics and bounding box metrics
> (even if in practice the two have been conflated most of the time).
>
> > - if the ascender and descender values are not explicitly defined, the
> > implementation will use the first, highest-priority component font to
> > determine the ascender and descender values according to the algorithm
> > defined in the "Baseline to Baseline Distances" section of the OT/OFF
> > "Recommendations" clause.
>
> This seems like a step in the right direction. Will need to review those
> recommendations again, though.
>
> I understand that Google did a lot of cross-browser testing of
> linespacing behaviour, and as a result came up with recommendations for
> their webfonts that differ from the recommendations we've worked with on
> Microsoft fonts for the past decade.
>
> J.
>
>
> --
>
> Tiro Typeworks        www.tiro.com
> Gulf Islands, BC      tiro at tiro.com
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