David J. Perry wrote:
>If I were to make a complete OT Greek font, with all the above as well
>as the combinations already in Unicode, which would provide better
>performance: substitutions or positioning via OT features?
>
There is a similar thread on the opentype@topica.com mailing list. My
argument is that you cannot expect positioning to be "more complete"
because it will form some combinations with apparently less work.
Regardless of whether you use substitution or positioning, it's the
testing of the actual combinations, alone and in context, that is the
bottleneck. The difference between the two methods (which can be
characterized as "combination at the factory" and "combination at the
installation site") are second order factors. In the case of CFF
outlines, which have a notion of subroutine, the size difference is not
that big. What is going to drive your choice is the ease of creating
combination glyph vs. the ease of creating GPOS lookups in your font
development environment, and how much you are willing to depend on
Unicode/OpenType support in the target environment (I know some software
that is more likely to handle substitutions than mark positioning).
Eric.
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