[mpeg-OTspec] New cmap format

[Opstad, Dave]

On Apr 3, 2012, at 2:21 PM, John Hudson wrote:

> I would like to explore the possibility of adding a new cmap format that 
> would perform the opposite operation, i.e. that would map from a single 
> Unicode codepoint to a sequence of two or more glyphs. My thinking 
> behind this is that it is currently necessary for fonts to include large 
> numbers of glyphs for Unicode precomposed diacritic characters, even 
> though the great majority of these can be represented using glyph 
> sequences and dynamic mark positioning. Although the effect of all these 
> glyphs of glyf or css table size is negligible if composites or 
> subroutines are used, they have a significant impact on font development 
> time -- not least in maintaining consistency between precomposed glyphs 
> and dynamic mark positioning -- and on GSUB and GPOS table size.
> 
> My idea is a cmap that would map from a single Unicode codepoint to a 
> sequence of two or more GIDs that, in combination with GPOS, would be 
> able to display that Unicode character. So instead of mapping
> 
> U+00C4 to /Adieresis/
> 
> the new format cmap would map
> 
> U+00C4 to /A/ /dieresiscob.cap/
> 
> Note how this kind if mapping can also bypass contextual GSUB 
> substitutions to access appropriate variant mark glyphs etc., which 
> should be more efficient.

The 'Zapf' table, documented here:

https://developer.apple.com/fonts/TTRefMan/RM06/Chap6Zapf.html

has as a component the FeatureInfo structure. Perhaps this would be interesting to look at another take on how this capability could be implemented? Apple ships many of their OS X fonts with a 'Zapf' table, although I don't know if they use the FeatureInfo structure.

Dave Opstad