Best practices for Vietnamese diacritics

[tribby]

Hi, just a question here regarding best practices. Glyphs will generate compound components like circumflexcomb_tildecomb but there is no codepoint for these - if the diacritics are the same but their position is simply different, is it preferable to take the approach described in the advanced diacritics tutorial? Do glyphsLib or other non-Glyphs ecosystems support this (making a choice between multiple anchors)?

[GeorgSeifert]

Those precomposed marks don’t need a code point. You still type them individually. The precomposed marks are mostly helping with the positioning. And they are build by the ccmp features. So you might need to update the OpenType features.

[clauseggers]

So far there is no other good way of setting double-decker diacritics more compactly in Glyphs.

[GeorgSeifert]

What do you mean?

[Tosche (Toshi Omagari)]

Mostly repeating what Georg already answered to the original post, but those double-decker diacritics are necessary only when you want to adjust them, either their shapes (e.g. for reducing heights) or positioning. Otherwise, you can simply use the existing singular ones. And the precomposed double-deckers are only used for the design stage, not when the user types text, meaning Unicode codeoints are unnecessary.

[clauseggers]

Were you asking me? I mean that there is currently no (automatic) way of having two sets of anchors: The normal set of top/_top for the singletons, and eg. having Glyphs use anchors called topDoubleDecker/_topDoubleDecker in the cases where a user type in more than one diacritic.

Last time I brought up the topic you never got back on it:

GPOS system of double-stacked diacritics?

I’m having a look at this now. There are a few issues: I created the @CombiningTopAccents class, but updating the features also puts a class by the same name into the ccmp feature. Should I just delete the class outside the ccmp feature? Is there is way to write the context so that the anchors are used both when the glyph comes before @CombiningTopAccents and when they come after @CombiningTopAccents? What do I do with the pre-composed glyphs? I can’t use the new anchors to place those diacrit…

I think I found out a way to answer question 2, by creating a group of all lower-case and all top diacritics.

[tribby]

Thank you Georg and Toshi.
I am still wondering if the ability to select which anchor a diacritic connects to is a Glyphs-specific concept. If it is, it would seem the method in the tutorial is unideal for working with other tools, roundtripping to UFO, etc?

[clauseggers]

Anchors are plain OpenType. In the documentation they are called ‘attachment points’ GPOS — Glyph Positioning Table (OpenType 1.9.1) - Typography | Microsoft Learn

[tribby]

Ah so the Glyphs UI for prioritizing attachments just compiles into OpenType feature code? Great!

[clauseggers]

Eventually all the ‘automagic’ features of Glyphs compile to OpenType. If you at some point want the gory details you can decompile the font binaries with TTX (utility application in FontTools)

[GeorgSeifert]

@clauseggers

I mean that there is currently no (automatic) way of having two sets of anchors: The normal set of top/_top for the singletons, and eg. having Glyphs use anchors called topDoubleDecker/_topDoubleDecker in the cases where a user type in more than one diacritic.

You can have multiple “top/_top” anchors by adding a suffix. e.g. “top.closer/_top.closer”. And then the next component/mark will use that.

For duble accenty, you usually need the move the first mark a bit down. The only way I know if how to do that is by adding a contextual anchor to all base glyphs:

This, lower anchor will be used, when there are two marks following the base.