[mpeg-OTspec] CFR ascender and descender

[Ken Lunde]

Christopher,

Your understanding about which component font to reference for these values if they are missing. Also, the word "typographic" in the descriptions is a clue as to which ascender and descender values to use, specifically these 'OS/2' table ones:

  OS/2.sTypoAscender
  OS/2.sTypoDescender

(These values should be identical to those in hhea.Ascender & hhea.Descender; at least, our OpenType tools make them so.)

Regards...

-- Ken

On Nov 15, 2013, at 5:11 AM, Chapman, Christopher <christopher.chapman at monotype.com> wrote:

> 
> Hi Folks,
> 
> 
> I have a question about the CFR ascender and descender metrics.
> 
> 
> The CFR spec. has the following descriptions of ascender & descender:
> 
> 
>     ascender = "string"
> 
>     Optional. The horizontal typographic ascent expressed as an integer.
> 
> 
>     descender = "string"
> 
>     Optional. The horizontal typographic descent expressed as an integer.
> 
> 
> My understanding is that if these optional attributes are missing from the CFR they are to be inherited from the first component font specified by either 'ComponentDef' or 'LanguagePreferredList' element.
> 
> 
> The OpenType spec. has the following possible sources of the ascender and descender metrics:
> 
> 
>     hhea.Ascender & hhea.Descender
> 
>     OS/2.sTypoAscender & OS/2.sTypoDescender
> 
>     OS/2.usWinAscent & OS/2.usWinDescent
> 
> 
> From which of these OpenType attributes should a CFR inherit its ascender and descender attributes?
> 
> 
> Thanks!
> 
> 
> Cheers,
> 
> Christopher
> 
> 
>