[mpeg-OTspec] CFR ascender and descender

[Ken Lunde]

Vladimir,

I feel that the most reasonable *default* (meaning when the values are not explicitly specified) values should come from OS/2.sTypoAscender and OS/2.sTypoDescender. If the CFR object author wants anything else, they should explicitly set the values. A CFR object author should have access to the fonts that are referenced, and if OS/2.sTypoAscender and OS/2.sTypoDescender are not set to the values that they desire, they should be overridden.

-- Ken

On Nov 19, 2013, at 6:09 AM, Levantovsky, Vladimir <vladimir.levantovsky at monotype.com> wrote:

> Thank you Christopher, you brought up a very good point.
> 
> Folks, just FYI - the latest corrigendum is currently under ballot so if there are any additional changes needed we can introduce them via ballot comments but we need to finalize the comments and do it quickly.
> 
> Ken, Tony - what are your thoughts on this particular issue, should we add a clarification in the spec language so that both CFR authors (when the ascender/descender values are provided by them) and the implementers (when the values are inherited from a highest priority component) would have a clear guidance on what fields to use as a reference?
> 
> Thank you,
> Vlad
> 
> > -----Original Message-----
> > From: mpeg-OTspec at yahoogroups.com [mailto:mpeg-OTspec at yahoogroups.com]
> > On Behalf Of Chapman, Christopher
> > Sent: Monday, November 18, 2013 4:02 PM
> > To: OTspec (mpeg-OTspec at yahoogroups.com)
> > Subject: RE: [mpeg-OTspec] CFR ascender and descender
> > 
> > Hi Folks,
> > 
> > Ken and John, thanks for your responses to my question.
> > 
> > The word "typographic" was not so helpful a clue because the Microsoft
> > typography webpage for the hhea table has:
> > FWORD	Ascender	Typographic ascent. (Distance from baseline of
> > highest ascender)
> > FWORD	Descender	Typographic descent. (Distance from baseline of
> > lowest descender)
> > [source: http://www.microsoft.com/typography/otspec/hhea.htm]
> > 
> > I checked 556 fonts that I had in my \Windows\Fonts directory and found
> > that in 395 of them (i.e. about 71%) hhea.ascender and hhea.descender
> > were not identical to OS/2.sTypoAscender and OS/2.sTypoDescender, so it
> > seems that not all font tools follow the practice of making those
> > attributes match.
> > 
> > I think it would be helpful to add some text to the CFR spec.
> > clarifying from which OpenType font metrics a CFR should inherit its
> > metrics if they are not explicitly specified in the CFR's XML,
> > especially in the case of ascender and descender. Thanks.
> > 
> > Cheers,
> > Christopher
> > 
> > 
> > ------------------------------------
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>