[mpeg-OTspec] Proposal related to Last Resort fonts

[John H. Jenkins]

On Apr 9, 2009, at 1:59 PM, Levantovsky, Vladimir wrote:

> My original impression (maybe incorrect) was that it would be okay  
> to have both standard cmap table support and ‘last resort’ cmap in  
> the same font. It’s feasible that one may want to create a Unicode  
> fonts where supported code points would be encoded using e.g. cmap  
> formats 0, 4 and 12, and unsupported code points would be encoded  
> using cmap format 13 (although I am still trying to wrap my head  
> around this as to why a different glyph rather than .notdef glyph  
> would be needed to convey the same thing, maybe we should say  
> something about it).
>

The only real reason to have a standard cmap subtable would be for  
compatibility with older parsers.  You're not likely to have a last  
resort font with the ability to cover, say, Latin properly.  The idea  
underlying the font is that it is a true font of last resort and will  
only be used when no other font in the system can properly display a  
character.  In Apple's case, we show a glyph specifying the Unicode  
block to which the character belongs, thus giving the user at least  
*some* information.

There's nothing to stop someone from implementing a font that covers  
one or more blocks properly and then uses a single glyph for  
everything in other blocks, of course.  It just seems like the result  
will be something of a chimera, neither fish nor fowl.

=====
John H. Jenkins
jenkins at apple.com

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