Most fonts that include Greek glyphs simply contain them and contain, if they support polythonic Greek, all glyphs with diacritics as well. So, for example, a capital letter eta with the signed iota remains such.
In some fonts, however, things are different. For example, in the Garamond Premiere the approach is totally different. The uppercase eta with signed iota is present in its slot (uni1FCC) as uppercase eta + lowercase iota. Then, there is a system that involves other glyphs (always using the same example, the capital age with the authentic signed iota) and a rather complex mechanism of substitutions.
Now, what is the advantage of this second type of approach, which is also absent in most fonts from Adobe itself?
Comments
Some typefaces, like Garamond Premiere Pro and my own Brill types provide for both conventions. Which form is treated as default will depend on the primary user community for whom the fonts are intended. In the case of the Brill types, this is academic publishing, mostly outside of Greece, so the postscript iota sign convention is the default.
Here’s how I did it in FontLab a few years ago.
@NickShinn Yes, I realized that the unicode value is the same. GaramondPremiere uses the suffix
PS
Since I don't need modern Greek as much as I do polytonic, in reality the small capital letter doesn't seem to be adopted in the quotations of ancient texts
In that tutorial it is specified:
1. The modern convention for all-caps settings is that all marks except the dialytika (diaeresis) are suppressed. This is a fairly recent convention related to the practice, standardised only in the 19th Century, of writing other marks to the left of the uppercase letters instead of above (or to the right!). This suppression is further complicated by contextual rules around conversion of the oxia/tonos mark on one letter to a dialytika on the next letter when displaying in all-caps, so e.g. εί > ΕΙ but έι > ΕΪ.
2. The varying historical conventions regarding suppression or display of marks on all-caps (and on smallcaps) can be handled via a stylistic set substitution or, as in the case of the Brill types, by enabling/disabling the Contextual Alternate ‘calt’ feature (I might change to a stylistic set feature in future, as this is a bit more robust). The contextual rule described above needs to be implemented in whatever feature is handling mark supporession.
3. Adobe Acrobat has a mechanism to parse glyph names in PDFs distilled from print streams, and to use these names to reconstruct the underlying character strings of text which are lost when PDFs are created in this way. When making fonts for clients, I always ask them whether they want this mechanism to be supported, because it can require duplicate glyphs in the font under different names, e.g. /A.c2sc/ and /a.smcp/ identical smallcap glyphs, one mapping back to the uppercase character and one to the lowercase. Brill opted to support the mechanism, which requires addition of a very large number of identical glyphs for uppercase or smallcap glyphs representing diacritic characters with marks suppressed.